Patent Publication Number: US-2022231943-A1

Title: Dynamic ip routing in a cloud environment

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to dynamic IP routing between customers and a public cloud provider. 
     BACKGROUND 
     Public cloud providers typically allow customers to use command line interfaces (CLIs), application programming interfaces (APIs), or software development kits (SDKs) to manage static IP routes. While this may suffice for simplistic workloads, it lacks the flexibility that most customers need for routing data transmissions. 
     Static IP routes are unable to adapt to changes in the state of the services. In fact, public cloud providers may be completely unaware of the state of the customer applications. For example, if a host owns a Service IP address A.1 and this host dies, the cloud provider is often unaware of this, and traffic destined for A.1 would now be dropped in the cloud. 
     Further, a customer may want to horizontally scale its service such that it can have “N” different hosts that all use the same A. 1  address. The customer may want the traffic destined for the A.1 address to be distributed across these “N” hosts. Today this may be achieved by using complex Layer-4-to-Layer-7 load balancers. However, load balancers are expensive and difficult to scale, and they may fail in complex ways. 
     BRIEF SUMMARY 
     The present disclosure relates generally to providing dynamic routing for data flows to a customer network hosted in the cloud. More particularly, techniques are described for allowing customers of a cloud service to add, remove, and manage data flow transmissions to a plurality of service hosts within the cloud. Various embodiments are described herein, including methods, systems, non-transitory computer-readable storage media storing programs, code, or instructions executable by one or more processors, and the like. 
     In certain embodiments, a plurality of compute instances may share a common virtual IP address. Each of the plurality of compute instances may advertise information to a respective network virtualization device (NVD). The information may include the IP address, the cost, and/or the active/standby status of the compute instance. The NVD may then provide the information to the control plane of a virtual cloud network (VCN), which may aggregate the information from the plurality of compute instances and generate a forwarding table, which may be sent to the NVDs. These techniques may allow a customer to automatically remove a compute instance whose service host has failed. These techniques may also allow a customer to add compute instances and to route data flows according to an active-standby operation, an equal cost active-active operation, or an unequal cost active-active operation. 
     Once the forwarding table has been generated and/or updated, an NVD that receives a request from the client host to deliver a data packet to a service host may reference the forwarding table to determine where to send the data packet. The NVD may also reference a history of data flow transmissions. The NVD may then send the data packet to one of the plurality of compute instances that are described in the forwarding table. 
     The method described above allows customers to control the state of the routing in their virtual network. This may increase the availability and traffic distribution that is available to each customer. Routes may automatically be added or deleted, instead of manually adding or removing hosts from the network. Further, the method may use a smartNIC instead of a load balancer to distribute the traffic load. Accordingly, the method may provide a fully distributed design that is scalable, has low latency, and has a low cost. 
     In certain embodiments, a first NVD of a plurality of NVDs receives first information about a first compute instance of a first service host, and sends the first information to a control plane of a VCN. The control plane receives the first information, updates a forwarding table based on the first information, identifies a subset of the plurality of NVDs to receive the forwarding table, and sends the forwarding table to the subset of the plurality of NVDs. Each NVD of the subset of the plurality of NVDs updates a respective forwarding table that is stored on the respective NVD as a function of the forwarding table received from the control plane. 
     The first information may be advertised by the first compute instance to the first NVD. The first information may be received by the first NVD as an absence of a keep-alive signal from the first compute instance. The first information may include an IP address of the first compute instance. The first information may also include a status of the first compute instance, and the status may be active or standby. The first information may also include a cost of the first compute instance. 
     The control plane may aggregate the first information received from the first NVD with additional information about additional compute instances received from other NVDs of the plurality of NVDs. The subset of the plurality of NVDs may include each NVD of the plurality of NVDs. 
     In some embodiments, a first NVD of a plurality of NVDs may receive a request from a client host to deliver a first data packet to a service host. The first NVD may identify a data flow that includes the first data packet, and may identify a plurality of potential destination compute instances for the first data packet based on a forwarding table that includes information about a plurality of compute instances of a plurality of service hosts that provide a same service. The plurality of potential destination compute instances may share a common virtual IP address. The first NVD may retrieve a history of data flow transmissions from the client host to the plurality of compute instances, and may select one of the plurality of potential destination compute instance as a destination compute instance for receipt of the first data packet based on at least one of the forwarding table or the history of data flow transmissions. The first NVD may send the first data packet to the destination compute instance, and may store information about the first data packet and the destination compute instance in the history of data flow transmissions. 
     Selecting the destination compute instance may include referencing the history of data flow transmissions to determine whether a second data packet of the data flow has been sent to a first one of the plurality of potential destination compute instances by the first NVD. When the second data packet has been sent to the first one of the plurality of potential destination compute instances, the destination compute instance may be selected as the first one of the plurality of potential destination compute instances. When the second data packet has not been sent to the first one of the plurality of potential destination compute instances, the destination compute instance may be selected based on a status of a compute instance at each potential destination compute instance, wherein the status is active or standby. Alternatively, when the second data packet has not been sent to the first one of the plurality of potential destination compute instances, the destination compute instance may be selected based on a cost associated with a compute instance at each potential destination compute instance. 
     In some embodiments, a first NVD of a plurality of NVDs may receive first information about a first compute instance of a plurality of compute instances. Each compute instance of the plurality of compute instances may be running on a respective service host of a plurality of service hosts. The first NVD may send the first information to a control plane of a VCN. The control plane may update a forwarding table based on the first information. The forwarding table may include additional information about the plurality of compute instances. The control plane may send the forwarding table to the plurality of NVDs. Each NVD of the plurality of NVDs may update a respective forwarding table that is stored on the respective NVD as a function of the forwarding table received from the control plane. 
     The first information may be advertised by the first compute instance to the first NVD. The first information may be received by the first NVD as an absence of a keep-alive signal from the first compute instance. The first information may include an IP address of the first compute instance. The first information may also include a status of the first compute instance, and the status may be active or standby. Alternatively, the first information may also include a cost of the first compute instance. 
     The first NVD may also receive a request from a client host to deliver a first data packet to a service host of the plurality of service hosts. The first NVD may identify a data flow that includes the first data packet, and may identify a plurality of potential compute instances for the first data packet based on the forwarding table. The first NVD may retrieve a history of data flow transmissions from the client host to the plurality of compute instances, and may select one of the potential destination compute instances as a destination compute instance for receipt of the first data packet based on at least one of the forwarding table or the history of data flow transmissions. The first NVD may send the first data packet to the destination compute instance, and may store second information about the first data packet and the destination compute instance in the history of data flow transmissions. 
     The foregoing, together with other features and embodiments, will become more apparent upon referring to the following specification, claims, and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high level diagram of a distributed environment showing a virtual or overlay cloud network hosted by a cloud service provider infrastructure according to certain embodiments. 
         FIG. 2  depicts a simplified architectural diagram of the physical components in the physical network within CSPI according to certain embodiments. 
         FIG. 3  shows an example arrangement within CSPI where a host machine is connected to multiple network virtualization devices (NVDs) according to certain embodiments. 
         FIG. 4  depicts connectivity between a host machine and an NVD for providing I/O virtualization for supporting multitenancy according to certain embodiments. 
         FIG. 5  depicts a simplified block diagram of a physical network provided by a CSPI according to certain embodiments. 
         FIG. 6  shows a simplified block diagram of a system incorporating an exemplary embodiment using active-standby operation. 
         FIG. 7  shows a simplified block diagram of a system incorporating an exemplary embodiment using equal cost active-active operation. 
         FIG. 8  shows a simplified block diagram of a system incorporating an exemplary embodiment using unequal cost active-active operation. 
         FIG. 9  shows a simplified flowchart depicting processing to establish or modify a forwarding table for distributing data flows among compute instances according to certain embodiments. 
         FIG. 10  shows a simplified flowchart  1000  depicting processing to distribute data flows among compute instances according to certain embodiments. 
         FIG. 11  is a block diagram illustrating one pattern for implementing a cloud infrastructure as a service system, according to at least one embodiment. 
         FIG. 12  is a block diagram illustrating another pattern for implementing a cloud infrastructure as a service system, according to at least one embodiment. 
         FIG. 13  is a block diagram illustrating another pattern for implementing a cloud infrastructure as a service system, according to at least one embodiment. 
         FIG. 14  is a block diagram illustrating another pattern for implementing a cloud infrastructure as a service system, according to at least one embodiment. 
         FIG. 15  is a block diagram illustrating an example computer system, according to at least one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, specific details are set forth in order to provide a thorough understanding of certain embodiments. However, it will be apparent that various embodiments may be practiced without these specific details. The figures and description are not intended to be restrictive. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. 
     As discussed above, the present disclosure relates generally to providing dynamic routing for data flows to a customer network hosted in the cloud. More particularly, techniques are described for allowing customers of a cloud service to add, remove, and manage data flow transmissions to a plurality of service hosts within the cloud. 
     In certain embodiments, a plurality of compute instances may share a common virtual IP address. This may increase the availability of a service host by decreasing the risk of loss of connectivity if one of the routes fails. Also, this may provide rapid and automatic fail-over if one of the routes fails. In addition, increased bandwidth may be provided via the cost function. 
     Each of the plurality of compute instances may advertise information to a respective network virtualization device (NVD). The information may include the IP address, the cost, and/or the active/standby status of the compute instance. The NVD may then provide the information to the control plane of a virtual cloud network (VCN), which may aggregate the information from the plurality of compute instances and generate a forwarding table, which may be sent to the NVDs. These techniques may allow a customer to automatically remove a compute instance whose service host has failed. These techniques may also allow a customer to add compute instances and to route data flows according to an active-standby operation, an equal cost active-active operation, or an unequal cost active-active operation. 
     Once the forwarding table has been generated and/or updated, an NVD that receives a request from the client host to deliver a data packet to a service host may reference the forwarding table to determine where to send the data packet. The NVD may also reference a history of data flow transmissions. The NVD may then send the data packet to one of the plurality of compute instances that are described in the forwarding table. 
     The term cloud service is generally used to refer to a service that is made available by a cloud services provider (CSP) to users or customers on demand (e.g., via a subscription model) using systems and infrastructure (cloud infrastructure) provided by the CSP. Typically, the servers and systems that make up the CSP&#39;s infrastructure are separate from the customer&#39;s own on-premise servers and systems. Customers can thus avail themselves of cloud services provided by the CSP without having to purchase separate hardware and software resources for the services. Cloud services are designed to provide a subscribing customer easy, scalable access to applications and computing resources without the customer having to invest in procuring the infrastructure that is used for providing the services. 
     There are several cloud service providers that offer various types of cloud services. There are various different types or models of cloud services including Software-as-a-Service (SaaS), Platform-as-a-Service (PaaS), Infrastructure-as-a-Service (IaaS), and others. 
     A customer can subscribe to one or more cloud services provided by a CSP. The customer can be any entity such as an individual, an organization, an enterprise, and the like. When a customer subscribes to or registers for a service provided by a CSP, a tenancy or an account is created for that customer. The customer can then, via this account, access the subscribed-to one or more cloud resources associated with the account. 
     As noted above, infrastructure as a service (IaaS) is one particular type of cloud computing service. In an IaaS model, the CSP provides infrastructure (referred to as cloud services provider infrastructure or CSPI) that can be used by customers to build their own customizable networks and deploy customer resources. The customer&#39;s resources and networks are thus hosted in a distributed environment by infrastructure provided by a CSP. This is different from traditional computing, where the customer&#39;s resources and networks are hosted by infrastructure provided by the customer. 
     The CSPI may comprise interconnected high-performance compute resources including various host machines, memory resources, and network resources that form a physical network, which is also referred to as a substrate network or an underlay network. The resources in CSPI may be spread across one or more data centers that may be geographically spread across one or more geographical regions. Virtualization software may be executed by these physical resources to provide a virtualized distributed environment. The virtualization creates an overlay network (also known as a software-based network, a software-defined network, or a virtual network) over the physical network. The CSPI physical network provides the underlying basis for creating one or more overlay or virtual networks on top of the physical network. The virtual or overlay networks can include one or more virtual cloud networks (VCNs). The virtual networks are implemented using software virtualization technologies (e.g., hypervisors, functions performed by network virtualization devices (NVDs) (e.g., smartNICs), top-of-rack (TOR) switches, smart TORs that implement one or more functions performed by an NVD, and other mechanisms) to create layers of network abstraction that can be run on top of the physical network. Virtual networks can take on many forms, including peer-to-peer networks, IP networks, and others. Virtual networks are typically either Layer-3 IP networks or Layer-2 VLANs. This method of virtual or overlay networking is often referred to as virtual or overlay Layer-3 networking. Examples of protocols developed for virtual networks include IP-in-IP (or Generic Routing Encapsulation (GRE)), Virtual Extensible LAN (VXLAN—IETF RFC 7348), Virtual Private Networks (VPNs) (e.g., MPLS Layer-3 Virtual Private Networks (RFC 4364)), VMware&#39;s NSX, GENEVE (Generic Network Virtualization Encapsulation), and others. 
     For IaaS, the infrastructure (CSPI) provided by a CSP can be configured to provide virtualized computing resources over a public network (e.g., the Internet). In an IaaS model, a cloud computing services provider can host the infrastructure components (e.g., servers, storage devices, network nodes (e.g., hardware), deployment software, platform virtualization (e.g., a hypervisor layer), or the like). In some cases, an IaaS provider may also supply a variety of services to accompany those infrastructure components (e.g., billing, monitoring, logging, security, load balancing and clustering, etc.). Thus, as these services may be policy-driven, IaaS users may be able to implement policies to drive load balancing to maintain application availability and performance. CSPI provides infrastructure and a set of complementary cloud services that enable customers to build and run a wide range of applications and services in a highly available hosted distributed environment. CSPI offers high-performance compute resources and capabilities and storage capacity in a flexible virtual network that is securely accessible from various networked locations such as from a customer&#39;s on-premises network. When a customer subscribes to or registers for an IaaS service provided by a CSP, the tenancy created for that customer is a secure and isolated partition within the CSPI where the customer can create, organize, and administer their cloud resources. 
     Customers can build their own virtual networks using compute, memory, and networking resources provided by CSPI. One or more customer resources or workloads, such as compute instances, can be deployed on these virtual networks. For example, a customer can use resources provided by CSPI to build one or multiple customizable and private virtual network(s) referred to as virtual cloud networks (VCNs). A customer can deploy one or more customer resources, such as compute instances, on a customer VCN. Compute instances can take the form of virtual machines, bare metal instances, and the like. The CSPI thus provides infrastructure and a set of complementary cloud services that enable customers to build and run a wide range of applications and services in a highly available virtual hosted environment. The customer does not manage or control the underlying physical resources provided by CSPI but has control over operating systems, storage, and deployed applications; and possibly limited control of select networking components (e.g., firewalls). 
     The CSP may provide a console that enables customers and network administrators to configure, access, and manage resources deployed in the cloud using CSPI resources. In certain embodiments, the console provides a web-based user interface that can be used to access and manage CSPI. In some implementations, the console is a web-based application provided by the CSP. 
     CSPI may support single-tenancy or multi-tenancy architectures. In a single tenancy architecture, a software (e.g., an application, a database) or a hardware component (e.g., a host machine or a server) serves a single customer or tenant. In a multi-tenancy architecture, a software or a hardware component serves multiple customers or tenants. Thus, in a multi-tenancy architecture, CSPI resources are shared between multiple customers or tenants. In a multi-tenancy situation, precautions are taken and safeguards put in place within CSPI to ensure that each tenant&#39;s data is isolated and remains invisible to other tenants. 
     In a physical network, a network endpoint (“endpoint”) refers to a computing device or system that is connected to a physical network and communicates back and forth with the network to which it is connected. A network endpoint in the physical network may be connected to a Local Area Network (LAN), a Wide Area Network (WAN), or other type of physical network. Examples of traditional endpoints in a physical network include modems, hubs, bridges, switches, routers, and other networking devices, physical computers (or host machines), and the like. Each physical device in the physical network has a fixed network address that can be used to communicate with the device. This fixed network address can be a Layer-2 address (e.g., a MAC address), a fixed Layer-3 address (e.g., an IP address), and the like. In a virtualized environment or in a virtual network, the endpoints can include various virtual endpoints such as virtual machines that are hosted by components of the physical network (e.g., hosted by physical host machines). These endpoints in the virtual network are addressed by overlay addresses such as overlay Layer-2 addresses (e.g., overlay MAC addresses) and overlay Layer-3 addresses (e.g., overlay IP addresses). Network overlays enable flexibility by allowing network managers to move around the overlay addresses associated with network endpoints using software management (e.g., via software implementing a control plane for the virtual network). Accordingly, unlike in a physical network, in a virtual network, an overlay address (e.g., an overlay IP address) can be moved from one endpoint to another using network management software. Since the virtual network is built on top of a physical network, communications between components in the virtual network involves both the virtual network and the underlying physical network. In order to facilitate such communications, the components of CSPI are configured to learn and store mappings that map overlay addresses in the virtual network to actual physical addresses in the substrate network, and vice versa. These mappings are then used to facilitate the communications. Customer traffic is encapsulated to facilitate routing in the virtual network. 
     Accordingly, physical addresses (e.g., physical IP addresses) are associated with components in physical networks and overlay addresses (e.g., overlay IP addresses) are associated with entities in virtual networks. Both the physical IP addresses and overlay IP addresses are types of real IP addresses. These are separate from virtual IP addresses, where a virtual IP address maps to multiple real IP addresses. A virtual IP address provides a  1 -to-many mapping between the virtual IP address and multiple real IP addresses. 
     The cloud infrastructure or CSPI is physically hosted in one or more data centers in one or more regions around the world. The CSPI may include components in the physical or substrate network and virtualized components (e.g., virtual networks, compute instances, virtual machines, etc.) that are in an virtual network built on top of the physical network components. In certain embodiments, the CSPI is organized and hosted in realms, regions and availability domains. A region is typically a localized geographic area that contains one or more data centers. Regions are generally independent of each other and can be separated by vast distances, for example, across countries or even continents. For example, a first region may be in Australia, another one in Japan, yet another one in India, and the like. CSPI resources are divided among regions such that each region has its own independent subset of CSPI resources. Each region may provide a set of core infrastructure services and resources, such as, compute resources (e.g., bare metal servers, virtual machine, containers and related infrastructure, etc.); storage resources (e.g., block volume storage, file storage, object storage, archive storage); networking resources (e.g., virtual cloud networks (VCNs), load balancing resources, connections to on-premise networks), database resources; edge networking resources (e.g., DNS); and access management and monitoring resources, and others. Each region generally has multiple paths connecting it to other regions in the realm. 
     Generally, an application is deployed in a region (i.e., deployed on infrastructure associated with that region) where it is most heavily used, because using nearby resources is faster than using distant resources. Applications can also be deployed in different regions for various reasons, such as redundancy to mitigate the risk of region-wide events such as large weather systems or earthquakes, to meet varying requirements for legal jurisdictions, tax domains, and other business or social criteria, and the like. 
     The data centers within a region can be further organized and subdivided into availability domains (ADs). An availability domain may correspond to one or more data centers located within a region. A region can be composed of one or more availability domains. In such a distributed environment, CSPI resources are either region-specific, such as a virtual cloud network (VCN), or availability domain-specific, such as a compute instance. 
     ADs within a region are isolated from each other, fault tolerant, and are configured such that they are very unlikely to fail simultaneously. This is achieved by the ADs not sharing critical infrastructure resources such as networking, physical cables, cable paths, cable entry points, etc., such that a failure at one AD within a region is unlikely to impact the availability of the other ADs within the same region. The ADs within the same region may be connected to each other by a low latency, high bandwidth network, which makes it possible to provide high-availability connectivity to other networks (e.g., the Internet, customers&#39; on-premise networks, etc.) and to build replicated systems in multiple ADs for both high-availability and disaster recovery. Cloud services use multiple ADs to ensure high availability and to protect against resource failure. As the infrastructure provided by the IaaS provider grows, more regions and ADs may be added with additional capacity. Traffic between availability domains is usually encrypted. 
     In certain embodiments, regions are grouped into realms. A realm is a logical collection of regions. Realms are isolated from each other and do not share any data. Regions in the same realm may communicate with each other, but regions in different realms cannot. A customer&#39;s tenancy or account with the CSP exists in a single realm and can be spread across one or more regions that belong to that realm. Typically, when a customer subscribes to an IaaS service, a tenancy or account is created for that customer in the customer-specified region (referred to as the “home” region) within a realm. A customer can extend the customer&#39;s tenancy across one or more other regions within the realm. A customer cannot access regions that are not in the realm where the customer&#39;s tenancy exists. 
     An IaaS provider can provide multiple realms, each realm catered to a particular set of customers or users. For example, a commercial realm may be provided for commercial customers. As another example, a realm may be provided for a specific country for customers within that country. As yet another example, a government realm may be provided for a government, and the like. For example, the government realm may be catered for a specific government and may have a heightened level of security than a commercial realm. For example, Oracle Cloud Infrastructure (OCI) currently offers a realm for commercial regions and two realms (e.g., FedRAMP authorized and IL5 authorized) for government cloud regions. 
     In certain embodiments, an AD can be subdivided into one or more fault domains. A fault domain is a grouping of infrastructure resources within an AD to provide anti-affinity. Fault domains allow for the distribution of compute instances such that the instances are not on the same physical hardware within a single AD. This is known as anti-affinity. A fault domain refers to a set of hardware components (computers, switches, and more) that share a single point of failure. A compute pool is logically divided up into fault domains. Due to this, a hardware failure or compute hardware maintenance event that affects one fault domain does not affect instances in other fault domains. Depending on the embodiment, the number of fault domains for each AD may vary. For instance, in certain embodiments each AD contains three fault domains. A fault domain acts as a logical data center within an AD. 
     When a customer subscribes to an IaaS service, resources from CSPI are provisioned for the customer and associated with the customer&#39;s tenancy. The customer can use these provisioned resources to build private networks and deploy resources on these networks. The customer networks that are hosted in the cloud by the CSPI are referred to as virtual cloud networks (VCNs). A customer can set up one or more virtual cloud networks (VCNs) using CSPI resources allocated for the customer. A VCN is a virtual or software defined private network. The customer resources that are deployed in the customer&#39;s VCN can include compute instances (e.g., virtual machines, bare-metal instances) and other resources. These compute instances may represent various customer workloads such as applications, load balancers, databases, and the like. A compute instance deployed on a VCN can communicate with public accessible endpoints (“public endpoints”) over a public network such as the Internet, with other instances in the same VCN or other VCNs (e.g., the customer&#39;s other VCNs, or VCNs not belonging to the customer), with the customer&#39;s on-premise data centers or networks, and with service endpoints, and other types of endpoints. 
     The CSP may provide various services using the CSPI. In some instances, customers of CSPI may themselves act like service providers and provide services using CSPI resources. A service provider may expose a service endpoint, which is characterized by identification information (e.g., an IP Address, a DNS name and port). A customer&#39;s resource (e.g., a compute instance) can consume a particular service by accessing a service endpoint exposed by the service for that particular service. These service endpoints are generally endpoints that are publicly accessible by users using public IP addresses associated with the endpoints via a public communication network such as the Internet. Network endpoints that are publicly accessible are also sometimes referred to as public endpoints. 
     In certain embodiments, a service provider may expose a service via an endpoint (sometimes referred to as a service endpoint) for the service. Customers of the service can then use this service endpoint to access the service. In certain implementations, a service endpoint provided for a service can be accessed by multiple customers that intend to consume that service. In other implementations, a dedicated service endpoint may be provided for a customer such that only that customer can access the service using that dedicated service endpoint. 
     In certain embodiments, when a VCN is created, it is associated with a private overlay Classless Inter-Domain Routing (CIDR) address space, which is a range of private overlay IP addresses that are assigned to the VCN (e.g., 10.0/16). A VCN includes associated subnets, route tables, and gateways. A VCN resides within a single region but can span one or more or all of the region&#39;s availability domains. A gateway is a virtual interface that is configured for a VCN and enables communication of traffic to and from the VCN to one or more endpoints outside the VCN. One or more different types of gateways may be configured for a VCN to enable communication to and from different types of endpoints. 
     A VCN can be subdivided into one or more sub-networks such as one or more subnets. A subnet is thus a unit of configuration or a subdivision that can be created within a VCN. A VCN can have one or multiple subnets. Each subnet within a VCN is associated with a contiguous range of overlay IP addresses (e.g., 10.0.0.0/24 and 10.0.1.0/24) that do not overlap with other subnets in that VCN and which represent an address space subset within the address space of the VCN. 
     Each compute instance is associated with a virtual network interface card (VNIC), that enables the compute instance to participate in a subnet of a VCN. A VNIC is a logical representation of physical Network Interface Card (NIC). In general. a VNIC is an interface between an entity (e.g., a compute instance, a service) and a virtual network. A VNIC exists in a subnet, has one or more associated IP addresses, and associated security rules or policies. A VNIC is equivalent to a Layer-2 port on a switch. A VNIC is attached to a compute instance and to a subnet within a VCN. A VNIC associated with a compute instance enables the compute instance to be a part of a subnet of a VCN and enables the compute instance to communicate (e.g., send and receive packets) with endpoints that are on the same subnet as the compute instance, with endpoints in different subnets in the VCN, or with endpoints outside the VCN. The VNIC associated with a compute instance thus determines how the compute instance connects with endpoints inside and outside the VCN. A VNIC for a compute instance is created and associated with that compute instance when the compute instance is created and added to a subnet within a VCN. For a subnet comprising a set of compute instances, the subnet contains the VNICs corresponding to the set of compute instances, each VNIC attached to a compute instance within the set of computer instances. 
     Each compute instance is assigned a private overlay IP address via the VNIC associated with the compute instance. This private overlay IP address is assigned to the VNIC that is associated with the compute instance when the compute instance is created and used for routing traffic to and from the compute instance. All VNICs in a given subnet use the same route table, security lists, and DHCP options. As described above, each subnet within a VCN is associated with a contiguous range of overlay IP addresses (e.g., 10.0.0.0/24 and 10.0.1.0/24) that do not overlap with other subnets in that VCN and which represent an address space subset within the address space of the VCN. For a VNIC on a particular subnet of a VCN, the private overlay IP address that is assigned to the VNIC is an address from the contiguous range of overlay IP addresses allocated for the subnet. 
     In certain embodiments, a compute instance may optionally be assigned additional overlay IP addresses in addition to the private overlay IP address, such as, for example, one or more public IP addresses if in a public subnet. These multiple addresses are assigned either on the same VNIC or over multiple VNICs that are associated with the compute instance. Each instance however has a primary VNIC that is created during instance launch and is associated with the overlay private IP address assigned to the instance—this primary VNIC cannot be removed. Additional VNICs, referred to as secondary VNICs, can be added to an existing instance in the same availability domain as the primary VNIC. All the VNICs are in the same availability domain as the instance. A secondary VNIC can be in a subnet in the same VCN as the primary VNIC, or in a different subnet that is either in the same VCN or a different one. 
     A compute instance may optionally be assigned a public IP address if it is in a public subnet. A subnet can be designated as either a public subnet or a private subnet at the time the subnet is created. A private subnet means that the resources (e.g., compute instances) and associated VNICs in the subnet cannot have public overlay IP addresses. A public subnet means that the resources and associated VNICs in the subnet can have public IP addresses. A customer can designate a subnet to exist either in a single availability domain or across multiple availability domains in a region or realm. 
     As described above, a VCN may be subdivided into one or more subnets. In certain embodiments, a Virtual Router (VR) configured for the VCN (referred to as the VCN VR or just VR) enables communications between the subnets of the VCN. For a subnet within a VCN, the VR represents a logical gateway for that subnet that enables the subnet (i.e., the compute instances on that subnet) to communicate with endpoints on other subnets within the VCN, and with other endpoints outside the VCN. The VCN VR is a logical entity that is configured to route traffic between VNICs in the VCN and virtual gateways (“gateways”) associated with the VCN. Gateways are further described below with respect to  FIG. 1 . A VCN VR is a Layer-3/IP Layer concept. In one embodiment, there is one VCN VR for a VCN where the VCN VR has potentially an unlimited number of ports addressed by IP addresses, with one port for each subnet of the VCN. In this manner, the VCN VR has a different IP address for each subnet in the VCN that the VCN VR is attached to. The VR is also connected to the various gateways configured for a VCN. In certain embodiments, a particular overlay IP address from the overlay IP address range for a subnet is reserved for a port of the VCN VR for that subnet. For example, consider a VCN having two subnets with associated address ranges 10.0/16 and 10.1/16, respectively. For the first subnet within the VCN with address range 10.0/16, an address from this range is reserved for a port of the VCN VR for that subnet. In some instances, the first IP address from the range may be reserved for the VCN VR. For example, for the subnet with overlay IP address range 10.0/16, IP address 10.0.0.1 may be reserved for a port of the VCN VR for that subnet. For the second subnet within the same VCN with address range 10.1/16, the VCN VR may have a port for that second subnet with IP address 10.1.0.1. The VCN VR has a different IP address for each of the subnets in the VCN. 
     In some other embodiments, each subnet within a VCN may have its own associated VR that is addressable by the subnet using a reserved or default IP address associated with the VR. The reserved or default IP address may, for example, be the first IP address from the range of IP addresses associated with that subnet. The VNICs in the subnet can communicate (e.g., send and receive packets) with the VR associated with the subnet using this default or reserved IP address. In such an embodiment, the VR is the ingress/egress point for that subnet. The VR associated with a subnet within the VCN can communicate with other VRs associated with other subnets within the VCN. The VRs can also communicate with gateways associated with the VCN. The VR function for a subnet is running on or executed by one or more NVDs executing VNICs functionality for VNICs in the subnet. 
     Route tables, security rules, and DHCP options may be configured for a VCN. Route tables are virtual route tables for the VCN and include rules to route traffic from subnets within the VCN to destinations outside the VCN by way of gateways or specially configured instances. A VCN&#39;s route tables can be customized to control how packets are forwarded/routed to and from the VCN. DHCP options refers to configuration information that is automatically provided to the instances when they boot up. 
     Security rules configured for a VCN represent overlay firewall rules for the VCN. The security rules can include ingress and egress rules, and specify the types of traffic (e.g., based upon protocol and port) that is allowed in and out of the instances within the VCN. The customer can choose whether a given rule is stateful or stateless. For instance, the customer can allow incoming SSH traffic from anywhere to a set of instances by setting up a stateful ingress rule with source CIDR 0.0.0.0/0, and destination TCP port 22. Security rules can be implemented using network security groups or security lists. A network security group consists of a set of security rules that apply only to the resources in that group. A security list, on the other hand, includes rules that apply to all the resources in any subnet that uses the security list. A VCN may be provided with a default security list with default security rules. DHCP options configured for a VCN provide configuration information that is automatically provided to the instances in the VCN when the instances boot up. 
     In certain embodiments, the configuration information for a VCN is determined and stored by a VCN Control Plane. The configuration information for a VCN may include, for example, information about: the address range associated with the VCN, subnets within the VCN and associated information, one or more VRs associated with the VCN, compute instances in the VCN and associated VNICs, NVDs executing the various virtualization network functions (e.g., VNICs, VRs, gateways) associated with the VCN, state information for the VCN, and other VCN-related information. In certain embodiments, a VCN Distribution Service publishes the configuration information stored by the VCN Control Plane, or portions thereof, to the NVDs. The distributed information may be used to update information (e.g., forwarding tables, routing tables, etc.) stored and used by the NVDs to forward packets to and from the compute instances in the VCN. 
     In certain embodiments, the creation of VCNs and subnets are handled by a VCN Control Plane (CP) and the launching of compute instances is handled by a Compute Control Plane. The Compute Control Plane is responsible for allocating the physical resources for the compute instance and then calls the VCN Control Plane to create and attach VNICs to the compute instance. The VCN CP also sends VCN data mappings to the VCN data plane that is configured to perform packet forwarding and routing functions. In certain embodiments, the VCN CP provides a distribution service that is responsible for providing updates to the VCN data plane. Examples of a VCN Control Plane are also depicted in  FIGS. 11, 12, 13, and 14  (see references  1116 ,  1216 ,  1316 , and  1416 ) and described below. 
     A customer may create one or more VCNs using resources hosted by CSPI. A compute instance deployed on a customer VCN may communicate with different endpoints. These endpoints can include endpoints that are hosted by CSPI and endpoints outside CSPI. 
     Various different architectures for implementing cloud-based service using CSPI are depicted in  FIGS. 1, 2, 3, 4, 5, 11, 12, 13, and 15 , and are described below.  FIG. 1  is a high level diagram of a distributed environment  100  showing an overlay or customer VCN hosted by CSPI according to certain embodiments. The distributed environment depicted in  FIG. 1  includes multiple components in the overlay network. Distributed environment  100  depicted in  FIG. 1  is merely an example and is not intended to unduly limit the scope of claimed embodiments. Many variations, alternatives, and modifications are possible. For example, in some implementations, the distributed environment depicted in  FIG. 1  may have more or fewer systems or components than those shown in  FIG. 1 , may combine two or more systems, or may have a different configuration or arrangement of systems. 
     As shown in the example depicted in  FIG. 1 , distributed environment  100  comprises CSPI  101  that provides services and resources that customers can subscribe to and use to build their virtual cloud networks (VCNs). In certain embodiments, CSPI  101  offers IaaS services to subscribing customers. The data centers within CSPI  101  may be organized into one or more regions. One example region “Region US”  102  is shown in  FIG. 1 . A customer has configured a customer VCN  104  for region  102 . The customer may deploy various compute instances on VCN  104 , where the compute instances may include virtual machines or bare metal instances. Examples of instances include applications, database, load balancers, and the like. 
     In the embodiment depicted in  FIG. 1 , customer VCN  104  comprises two subnets, namely, “Subnet- 1 ” and “Subnet- 2 ”, each subnet with its own CIDR IP address range. In  FIG. 1 , the overlay IP address range for Subnet- 1  is 10.0/16 and the address range for Subnet- 2  is 10.1/16. A VCN Virtual Router  105  represents a logical gateway for the VCN that enables communications between subnets of the VCN  104 , and with other endpoints outside the VCN. VCN VR  105  is configured to route traffic between VNICs in VCN  104  and gateways associated with VCN  104 . VCN VR  105  provides a port for each subnet of VCN  104 . For example, VR  105  may provide a port with IP address 10.0.0.1 for Subnet- 1  and a port with IP address 10.1.0.1 for Subnet- 2 . 
     Multiple compute instances may be deployed on each subnet, where the compute instances can be virtual machine instances, and/or bare metal instances. The compute instances in a subnet may be hosted by one or more host machines within CSPI  101 . A compute instance participates in a subnet via a VNIC associated with the compute instance. For example, as shown in  FIG. 1 , a compute instance C 1  is part of Subnet- 1  via a VNIC associated with the compute instance. Likewise, compute instance C 2  is part of Subnet- 1  via a VNIC associated with C 2 . In a similar manner, multiple compute instances, which may be virtual machine instances or bare metal instances, may be part of Subnet- 1 . Via its associated VNIC, each compute instance is assigned a private overlay IP address and a MAC address. For example, in  FIG. 1 , compute instance C 1  has an overlay IP address of 10.0.0.2 and a MAC address of M 1 , while compute instance C 2  has an private overlay IP address of 10.0.0.3 and a MAC address of M 2 . Each compute instance in Subnet- 1 , including compute instances C 1  and C 2 , has a default route to VCN VR  105  using IP address  10 . 0 . 0 . 1 , which is the IP address for a port of VCN VR  105  for Subnet- 1 . 
     Subnet- 2  can have multiple compute instances deployed on it, including virtual machine instances and/or bare metal instances. For example, as shown in  FIG. 1 , compute instances D 1  and D 2  are part of Subnet- 2  via VNICs associated with the respective compute instances. In the embodiment depicted in  FIG. 1 , compute instance D 1  has an overlay IP address of 10.1.0.2 and a MAC address of MM 1 , while compute instance D 2  has an private overlay IP address of 10.1.0.3 and a MAC address of MM 2 . Each compute instance in Subnet- 2 , including compute instances D 1  and D 2 , has a default route to VCN VR  105  using IP address 10.1.0.1, which is the IP address for a port of VCN VR  105  for Subnet- 2 . 
     VCN A  104  may also include one or more load balancers. For example, a load balancer may be provided for a subnet and may be configured to load balance traffic across multiple compute instances on the subnet. A load balancer may also be provided to load balance traffic across subnets in the VCN. 
     A particular compute instance deployed on VCN  104  can communicate with various different endpoints. These endpoints may include endpoints that are hosted by CSPI  200  and endpoints outside CSPI  200 . Endpoints that are hosted by CSPI  101  may include: an endpoint on the same subnet as the particular compute instance (e.g., communications between two compute instances in Subnet- 1 ); an endpoint on a different subnet but within the same VCN (e.g., communication between a compute instance in Subnet- 1  and a compute instance in Subnet- 2 ); an endpoint in a different VCN in the same region (e.g., communications between a compute instance in Subnet- 1  and an endpoint in a VCN in the same region  106  or  110 , communications between a compute instance in Subnet- 1  and an endpoint in service network  110  in the same region); or an endpoint in a VCN in a different region (e.g., communications between a compute instance in Subnet- 1  and an endpoint in a VCN in a different region  108 ). A compute instance in a subnet hosted by CSPI  101  may also communicate with endpoints that are not hosted by CSPI  101  (i.e., are outside CSPI  101 ). These outside endpoints include endpoints in the customer&#39;s on-premise network  116 , endpoints within other remote cloud hosted networks  118 , public endpoints  114  accessible via a public network such as the Internet, and other endpoints. 
     Communications between compute instances on the same subnet are facilitated using VNICs associated with the source compute instance and the destination compute instance. For example, compute instance C 1  in Subnet- 1  may want to send packets to compute instance C 2  in Subnet- 1 . For a packet originating at a source compute instance and whose destination is another compute instance in the same subnet, the packet is first processed by the VNIC associated with the source compute instance. Processing performed by the VNIC associated with the source compute instance can include determining destination information for the packet from the packet headers, identifying any policies (e.g., security lists) configured for the VNIC associated with the source compute instance, determining a next hop for the packet, performing any packet encapsulation/decapsulation functions as needed, and then forwarding/routing the packet to the next hop with the goal of facilitating communication of the packet to its intended destination. When the destination compute instance is in the same subnet as the source compute instance, the VNIC associated with the source compute instance is configured to identify the VNIC associated with the destination compute instance and forward the packet to that VNIC for processing. The VNIC associated with the destination compute instance is then executed and forwards the packet to the destination compute instance. 
     For a packet to be communicated from a compute instance in a subnet to an endpoint in a different subnet in the same VCN, the communication is facilitated by the VNICs associated with the source and destination compute instances and the VCN VR. For example, if compute instance C 1  in Subnet- 1  in  FIG. 1  wants to send a packet to compute instance D 1  in Subnet- 2 , the packet is first processed by the VNIC associated with compute instance C 1 . The VNIC associated with compute instance C 1  is configured to route the packet to the VCN VR  105  using default route or port 10.0.0.1 of the VCN VR. VCN VR  105  is configured to route the packet to Subnet- 2  using port 10.1.0.1. The packet is then received and processed by the VNIC associated with D 1  and the VNIC forwards the packet to compute instance D 1 . 
     For a packet to be communicated from a compute instance in VCN  104  to an endpoint that is outside VCN  104 , the communication is facilitated by the VNIC associated with the source compute instance, VCN VR  105 , and gateways associated with VCN  104 . One or more types of gateways may be associated with VCN  104 . A gateway is an interface between a VCN and another endpoint, where the another endpoint is outside the VCN. A gateway is a Layer- 3 /IP layer concept and enables a VCN to communicate with endpoints outside the VCN. A gateway thus facilitates traffic flow between a VCN and other VCNs or networks. Various different types of gateways may be configured for a VCN to facilitate different types of communications with different types of endpoints. Depending upon the gateway, the communications may be over public networks (e.g., the Internet) or over private networks. Various communication protocols may be used for these communications. 
     For example, compute instance C 1  may want to communicate with an endpoint outside VCN  104 . The packet may be first processed by the VNIC associated with source compute instance C 1 . The VNIC processing determines that the destination for the packet is outside the Subnet- 1  of C 1 . The VNIC associated with C 1  may forward the packet to VCN VR  105  for VCN  104 . VCN VR  105  then processes the packet and as part of the processing, based upon the destination for the packet, determines a particular gateway associated with VCN  104  as the next hop for the packet. VCN VR  105  may then forward the packet to the particular identified gateway. For example, if the destination is an endpoint within the customer&#39;s on-premise network, then the packet may be forwarded by VCN VR  105  to Dynamic Routing Gateway (DRG) gateway  122  configured for VCN  104 . The packet may then be forwarded from the gateway to a next hop to facilitate communication of the packet to it final intended destination. 
     Various different types of gateways may be configured for a VCN. Examples of gateways that may be configured for a VCN are depicted in  FIG. 1  and described below. Examples of gateways associated with a VCN are also depicted in  FIGS. 11, 12, 13, and 14  (for example, gateways referenced by reference numbers  1134 ,  1136 ,  1138 ,  1234 ,  1236 ,  1238 ,  1334 ,  1336 ,  1338 ,  1434 ,  1436 , and  1438 ) and described below. As shown in the embodiment depicted in  FIG. 1 , a Dynamic Routing Gateway (DRG)  122  may be added to or be associated with customer VCN  104  and provides a path for private network traffic communication between customer VCN  104  and another endpoint, where the another endpoint can be the customer&#39;s on-premise network  116 , a VCN  108  in a different region of CSPI  101 , or other remote cloud networks  118  not hosted by CSPI  101 . Customer on-premise network  116  may be a customer network or a customer data center built using the customer&#39;s resources. Access to customer on-premise network  116  is generally very restricted. For a customer that has both a customer on-premise network  116  and one or more VCNs  104  deployed or hosted in the cloud by CSPI  101 , the customer may want their on-premise network  116  and their cloud-based VCN  104  to be able to communicate with each other. This enables a customer to build an extended hybrid environment encompassing the customer&#39;s VCN  104  hosted by CSPI  101  and their on-premises network  116 . DRG  122  enables this communication. To enable such communications, a communication channel  124  is set up where one endpoint of the channel is in customer on-premise network  116  and the other endpoint is in CSPI  101  and connected to customer VCN  104 . Communication channel  124  can be over public communication networks such as the Internet or private communication networks. Various different communication protocols may be used such as IPsec VPN technology over a public communication network such as the Internet, Oracle&#39;s FastConnect technology that uses a private network instead of a public network, and others. The device or equipment in customer on-premise network  116  that forms one end point for communication channel  124  is referred to as the customer premise equipment (CPE), such as CPE  126  depicted in  FIG. 1 . On the CSPI  101  side, the endpoint may be a host machine executing DRG  122 . 
     In certain embodiments, a Remote Peering Connection (RPC) can be added to a DRG, which allows a customer to peer one VCN with another VCN in a different region. Using such an RPC, customer VCN  104  can use DRG  122  to connect with a VCN  108  in another region. DRG  122  may also be used to communicate with other remote cloud networks  118 , not hosted by CSPI  101  such as a Microsoft Azure cloud, Amazon AWS cloud, and others. 
     As shown in  FIG. 1 , an Internet Gateway (IGW)  120  may be configured for customer VCN  104  the enables a compute instance on VCN  104  to communicate with public endpoints  114  accessible over a public network such as the Internet. IGW  1120  is a gateway that connects a VCN to a public network such as the Internet. IGW  120  enables a public subnet (where the resources in the public subnet have public overlay IP addresses) within a VCN, such as VCN  104 , direct access to public endpoints  112  on a public network  114  such as the Internet. Using IGW  120 , connections can be initiated from a subnet within VCN  104  or from the Internet. 
     A Network Address Translation (NAT) gateway  128  can be configured for customer&#39;s VCN  104  and enables cloud resources in the customer&#39;s VCN, which do not have dedicated public overlay IP addresses, access to the Internet and it does so without exposing those resources to direct incoming Internet connections (e.g., L4-L7 connections). This enables a private subnet within a VCN, such as private Subnet- 1  in VCN  104 , with private access to public endpoints on the Internet. In NAT gateways, connections can be initiated only from the private subnet to the public Internet and not from the Internet to the private subnet. 
     In certain embodiments, a Service Gateway (SGW)  126  can be configured for customer VCN  104  and provides a path for private network traffic between VCN  104  and supported services endpoints in a service network  110 . In certain embodiments, service network  110  may be provided by the CSP and may provide various services. An example of such a service network is Oracle&#39;s Services Network, which provides various services that can be used by customers. For example, a compute instance (e.g., a database system) in a private subnet of customer VCN  104  can back up data to a service endpoint (e.g., Object Storage) without needing public IP addresses or access to the Internet. In certain embodiments, a VCN can have only one SGW, and connections can only be initiated from a subnet within the VCN and not from service network  110 . If a VCN is peered with another, resources in the other VCN typically cannot access the SGW. Resources in on-premises networks that are connected to a VCN with FastConnect or VPN Connect can also use the service gateway configured for that VCN. 
     In certain implementations, SGW  126  uses the concept of a service Classless Inter-Domain Routing (CIDR) label, which is a string that represents all the regional public IP address ranges for the service or group of services of interest. The customer uses the service CIDR label when they configure the SGW and related route rules to control traffic to the service. The customer can optionally utilize it when configuring security rules without needing to adjust them if the service&#39;s public IP addresses change in the future. 
     A Local Peering Gateway (LPG)  132  is a gateway that can be added to customer VCN  104  and enables VCN  104  to peer with another VCN in the same region. Peering means that the VCNs communicate using private IP addresses, without the traffic traversing a public network such as the Internet or without routing the traffic through the customer&#39;s on-premises network  116 . In preferred embodiments, a VCN has a separate LPG for each peering it establishes. Local Peering or VCN Peering is a common practice used to establish network connectivity between different applications or infrastructure management functions. 
     Service providers, such as providers of services in service network  110 , may provide access to services using different access models. According to a public access model, services may be exposed as public endpoints that are publicly accessible by compute instance in a customer VCN via a public network such as the Internet and or may be privately accessible via SGW  126 . According to a specific private access model, services are made accessible as private IP endpoints in a private subnet in the customer&#39;s VCN. This is referred to as a Private Endpoint (PE) access and enables a service provider to expose their service as an instance in the customer&#39;s private network. A Private Endpoint resource represents a service within the customer&#39;s VCN. Each PE manifests as a VNIC (referred to as a PE-VNIC, with one or more private IPs) in a subnet chosen by the customer in the customer&#39;s VCN. A PE thus provides a way to present a service within a private customer VCN subnet using a VNIC. Since the endpoint is exposed as a VNIC, all the features associates with a VNIC such as routing rules, security lists, etc., are now available for the PE VNIC. 
     A service provider can register their service to enable access through a PE. The provider can associate policies with the service that restricts the service&#39;s visibility to the customer tenancies. A provider can register multiple services under a single virtual IP address (VIP), especially for multi-tenant services. There may be multiple such private endpoints (in multiple VCNs) that represent the same service. 
     Compute instances in the private subnet can then use the PE VNIC&#39;s private IP address or the service DNS name to access the service. Compute instances in the customer VCN can access the service by sending traffic to the private IP address of the PE in the customer VCN. A Private Access Gateway (PAGW)  130  is a gateway resource that can be attached to a service provider VCN (e.g., a VCN in service network  110 ) that acts as an ingress/egress point for all traffic from/to customer subnet private endpoints. PAGW  130  enables a provider to scale the number of PE connections without utilizing its internal IP address resources. A provider needs only configure one PAGW for any number of services registered in a single VCN. Providers can represent a service as a private endpoint in multiple VCNs of one or more customers. From the customer&#39;s perspective, the PE VNIC, which, instead of being attached to a customer&#39;s instance, appears attached to the service with which the customer wishes to interact. The traffic destined to the private endpoint is routed via PAGW  130  to the service. These are referred to as customer-to-service private connections (C2S connections). 
     The PE concept can also be used to extend the private access for the service to customer&#39;s on-premises networks and data centers, by allowing the traffic to flow through FastConnect/IPsec links and the private endpoint in the customer VCN. Private access for the service can also be extended to the customer&#39;s peered VCNs, by allowing the traffic to flow between LPG  132  and the PE in the customer&#39;s VCN. 
     A customer can control routing in a VCN at the subnet level, so the customer can specify which subnets in the customer&#39;s VCN, such as VCN  104 , use each gateway. A VCN&#39;s route tables are used to decide if traffic is allowed out of a VCN through a particular gateway. For example, in a particular instance, a route table for a public subnet within customer VCN  104  may send non-local traffic through IGW  120 . The route table for a private subnet within the same customer VCN  104  may send traffic destined for CSP services through SGW  126 . All remaining traffic may be sent via the NAT gateway  128 . Route tables only control traffic going out of a VCN. 
     Security lists associated with a VCN are used to control traffic that comes into a VCN via a gateway via inbound connections. All resources in a subnet use the same route table and security lists. Security lists may be used to control specific types of traffic allowed in and out of instances in a subnet of a VCN. Security list rules may comprise ingress (inbound) and egress (outbound) rules. For example, an ingress rule may specify an allowed source address range, while an egress rule may specify an allowed destination address range. Security rules may specify a particular protocol (e.g., TCP, ICMP), a particular port (e.g., 22 for SSH, 3389 for Windows RDP), etc. In certain implementations, an instance&#39;s operating system may enforce its own firewall rules that are aligned with the security list rules. Rules may be stateful (e.g., a connection is tracked and the response is automatically allowed without an explicit security list rule for the response traffic) or stateless. 
     Access from a customer VCN (i.e., by a resource or compute instance deployed on VCN  104 ) can be categorized as public access, private access, or dedicated access. Public access refers to an access model where a public IP address or a NAT is used to access a public endpoint. Private access enables customer workloads in VCN  104  with private IP addresses (e.g., resources in a private subnet) to access services without traversing a public network such as the Internet. In certain embodiments, CSPI  101  enables customer VCN workloads with private IP addresses to access the (public service endpoints of) services using a service gateway. A service gateway thus offers a private access model by establishing a virtual link between the customer&#39;s VCN and the service&#39;s public endpoint residing outside the customer&#39;s private network. 
     Additionally, CSPI may offer dedicated public access using technologies such as FastConnect public peering where customer on-premises instances can access one or more services in a customer VCN using a FastConnect connection and without traversing a public network such as the Internet. CSPI also may also offer dedicated private access using FastConnect private peering where customer on-premises instances with private IP addresses can access the customer&#39;s VCN workloads using a FastConnect connection. FastConnect is a network connectivity alternative to using the public Internet to connect a customer&#39;s on-premise network to CSPI and its services. FastConnect provides an easy, elastic, and economical way to create a dedicated and private connection with higher bandwidth options and a more reliable and consistent networking experience when compared to Internet-based connections. 
       FIG. 1  and the accompanying description above describes various virtualized components in an example virtual network. As described above, the virtual network is built on the underlying physical or substrate network.  FIG. 2  depicts a simplified architectural diagram of the physical components in the physical network within CSPI  200  that provide the underlay for the virtual network according to certain embodiments. As shown, CSPI  200  provides a distributed environment comprising components and resources (e.g., compute, memory, and networking resources) provided by a cloud service provider (CSP). These components and resources are used to provide cloud services (e.g., IaaS services) to subscribing customers, i.e., customers that have subscribed to one or more services provided by the CSP. Based upon the services subscribed to by a customer, a subset of resources (e.g., compute, memory, and networking resources) of CSPI  200  are provisioned for the customer. Customers can then build their own cloud-based (i.e., CSPI-hosted) customizable and private virtual networks using physical compute, memory, and networking resources provided by CSPI  200 . As previously indicated, these customer networks are referred to as virtual cloud networks (VCNs). A customer can deploy one or more customer resources, such as compute instances, on these customer VCNs. Compute instances can be in the form of virtual machines, bare metal instances, and the like. CSPI  200  provides infrastructure and a set of complementary cloud services that enable customers to build and run a wide range of applications and services in a highly available hosted environment. 
     In the example embodiment depicted in  FIG. 2 , the physical components of CSPI  200  include one or more physical host machines or physical servers (e.g.,  202 ,  206 ,  208 ), network virtualization devices (NVDs) (e.g.,  210 ,  212 ), top-of-rack (TOR) switches (e.g.,  214 ,  216 ), and a physical network (e.g.,  218 ), and switches in physical network  218 . The physical host machines or servers may host and execute various compute instances that participate in one or more subnets of a VCN. The compute instances may include virtual machine instances, and bare metal instances. For example, the various compute instances depicted in  FIG. 1  may be hosted by the physical host machines depicted in  FIG. 2 . The virtual machine compute instances in a VCN may be executed by one host machine or by multiple different host machines. The physical host machines may also host virtual host machines, container-based hosts or functions, and the like. The VNICs and VCN VR depicted in  FIG. 1  may be executed by the NVDs depicted in  FIG. 2 . The gateways depicted in  FIG. 1  may be executed by the host machines and/or by the NVDs depicted in  FIG. 2 . 
     The host machines or servers may execute a hypervisor (also referred to as a virtual machine monitor or VMM) that creates and enables a virtualized environment on the host machines. The virtualization or virtualized environment facilitates cloud-based computing. One or more compute instances may be created, executed, and managed on a host machine by a hypervisor on that host machine. The hypervisor on a host machine enables the physical computing resources of the host machine (e.g., compute, memory, and networking resources) to be shared between the various compute instances executed by the host machine. 
     For example, as depicted in  FIG. 2 , host machines  202  and  208  execute hypervisors  260  and  266 , respectively. These hypervisors may be implemented using software, firmware, or hardware, or combinations thereof. Typically, a hypervisor is a process or a software layer that sits on top of the host machine&#39;s operating system (OS), which in turn executes on the hardware processors of the host machine. The hypervisor provides a virtualized environment by enabling the physical computing resources (e.g., processing resources such as processors/cores, memory resources, networking resources) of the host machine to be shared among the various virtual machine compute instances executed by the host machine. For example, in  FIG. 2 , hypervisor  260  may sit on top of the OS of host machine  202  and enables the computing resources (e.g., processing, memory, and networking resources) of host machine  202  to be shared between compute instances (e.g., virtual machines) executed by host machine  202 . A virtual machine can have its own operating system (referred to as a guest operating system), which may be the same as or different from the OS of the host machine. The operating system of a virtual machine executed by a host machine may be the same as or different from the operating system of another virtual machine executed by the same host machine. A hypervisor thus enables multiple operating systems to be executed alongside each other while sharing the same computing resources of the host machine. The host machines depicted in  FIG. 2  may have the same or different types of hypervisors. 
     A compute instance can be a virtual machine instance or a bare metal instance. In  FIG. 2 , compute instances  268  on host machine  202  and  274  on host machine  208  are examples of virtual machine instances. Host machine  206  is an example of a bare metal instance that is provided to a customer. 
     In certain instances, an entire host machine may be provisioned to a single customer, and all of the one or more compute instances (either virtual machines or bare metal instance) hosted by that host machine belong to that same customer. In other instances, a host machine may be shared between multiple customers (i.e., multiple tenants). In such a multi-tenancy scenario, a host machine may host virtual machine compute instances belonging to different customers. These compute instances may be members of different VCNs of different customers. In certain embodiments, a bare metal compute instance is hosted by a bare metal server without a hypervisor. When a bare metal compute instance is provisioned, a single customer or tenant maintains control of the physical CPU, memory, and network interfaces of the host machine hosting the bare metal instance and the host machine is not shared with other customers or tenants. 
     As previously described, each compute instance that is part of a VCN is associated with a VNIC that enables the compute instance to become a member of a subnet of the VCN. The VNIC associated with a compute instance facilitates the communication of packets or frames to and from the compute instance. A VNIC is associated with a compute instance when the compute instance is created. In certain embodiments, for a compute instance executed by a host machine, the VNIC associated with that compute instance is executed by an NVD connected to the host machine. For example, in  FIG. 2 , host machine  202  executes a virtual machine compute instance  268  that is associated with VNIC  276 , and VNIC  276  is executed by NVD  210  connected to host machine  202 . As another example, bare metal instance  272  hosted by host machine  206  is associated with VNIC  280  that is executed by NVD  212  connected to host machine  206 . As yet another example, VNIC  284  is associated with compute instance  274  executed by host machine  208 , and VNIC  284  is executed by NVD  212  connected to host machine  208 . 
     For compute instances hosted by a host machine, an NVD connected to that host machine also executes VCN VRs corresponding to VCNs of which the compute instances are members. For example, in the embodiment depicted in  FIG. 2 , NVD  210  executes VCN VR  277  corresponding to the VCN of which compute instance  268  is a member. NVD  212  may also execute one or more VCN VRs  283  corresponding to VCNs corresponding to the compute instances hosted by host machines  206  and  208 . 
     A host machine may include one or more network interface cards (NIC) that enable the host machine to be connected to other devices. A NIC on a host machine may provide one or more ports (or interfaces) that enable the host machine to be communicatively connected to another device. For example, a host machine may be connected to an NVD using one or more ports (or interfaces) provided on the host machine and on the NVD. A host machine may also be connected to other devices such as another host machine. 
     For example, in  FIG. 2 , host machine  202  is connected to NVD  210  using link  220  that extends between a port  234  provided by a NIC  232  of host machine  202  and between a port  236  of NVD  210 . Host machine  206  is connected to NVD  212  using link  224  that extends between a port  246  provided by a NIC  244  of host machine  206  and between a port  248  of NVD  212 . Host machine  208  is connected to NVD  212  using link  226  that extends between a port  252  provided by a NIC  250  of host machine  208  and between a port  254  of NVD  212 . 
     The NVDs are in turn connected via communication links to top-of-the-rack (TOR) switches, which are connected to physical network  218  (also referred to as the switch fabric). In certain embodiments, the links between a host machine and an NVD, and between an NVD and a TOR switch are Ethernet links. For example, in  FIG. 2 , NVDs  210  and  212  are connected to TOR switches  214  and  216 , respectively, using links  228  and  230 . In certain embodiments, the links  220 ,  224 ,  226 ,  228 , and  230  are Ethernet links. The collection of host machines and NVDs that are connected to a TOR is sometimes referred to as a rack. 
     Physical network  218  provides a communication fabric that enables TOR switches to communicate with each other. Physical network  218  can be a multi-tiered network. In certain implementations, physical network  218  is a multi-tiered Clos network of switches, with TOR switches  214  and  216  representing the leaf level nodes of the multi-tiered and multi-node physical switching network  218 . Different Clos network configurations are possible including but not limited to a 2-tier network, a 3-tier network, a 4-tier network, a 5-tier network, and in general a “n”-tiered network. An example of a Clos network is depicted in  FIG. 5  and described below. 
     Various different connection configurations are possible between host machines and NVDs such as one-to-one configuration, many-to-one configuration, one-to-many configuration, and others. In a one-to-one configuration implementation, each host machine is connected to its own separate NVD. For example, in  FIG. 2 , host machine  202  is connected to NVD  210  via NIC  232  of host machine  202 . In a many-to-one configuration, multiple host machines are connected to one NVD. For example, in  FIG. 2 , host machines  206  and  208  are connected to the same NVD  212  via NICs  244  and  250 , respectively. 
     In a one-to-many configuration, one host machine is connected to multiple NVDs.  FIG. 3  shows an example within CSPI  300  where a host machine is connected to multiple NVDs. As shown in  FIG. 3 , host machine  302  comprises a network interface card (NIC)  304  that includes multiple ports  306  and  308 . Host machine  300  is connected to a first NVD  310  via port  306  and link  320 , and connected to a second NVD  312  via port  308  and link  322 . Ports  306  and  308  may be Ethernet ports and the links  320  and  322  between host machine  302  and NVDs  310  and  312  may be Ethernet links. NVD  310  is in turn connected to a first TOR switch  314  and NVD  312  is connected to a second TOR switch  316 . The links between NVDs  310  and  312 , and TOR switches  314  and  316  may be Ethernet links. TOR switches  314  and  316  represent the Tier-0 switching devices in multi-tiered physical network  318 . 
     The arrangement depicted in  FIG. 3  provides two separate physical network paths to and from physical switch network  318  to host machine  302 : a first path traversing TOR switch  314  to NVD  310  to host machine  302 , and a second path traversing TOR switch  316  to NVD  312  to host machine  302 . The separate paths provide for enhanced availability (referred to as high availability) of host machine  302 . If there are problems in one of the paths (e.g., a link in one of the paths goes down) or devices (e.g., a particular NVD is not functioning), then the other path may be used for communications to/from host machine  302 . 
     In the configuration depicted in  FIG. 3 , the host machine is connected to two different NVDs using two different ports provided by a NIC of the host machine. In other embodiments, a host machine may include multiple NICs that enable connectivity of the host machine to multiple NVDs. 
     Referring back to  FIG. 2 , an NVD is a physical device or component that performs one or more network and/or storage virtualization functions. An NVD may be any device with one or more processing units (e.g., CPUs, Network Processing Units (NPUs), FPGAs, packet processing pipelines, etc.), memory including cache, and ports. The various virtualization functions may be performed by software/firmware executed by the one or more processing units of the NVD. 
     An NVD may be implemented in various different forms. For example, in certain embodiments, an NVD is implemented as an interface card referred to as a smartNIC or an intelligent NIC with an embedded processor onboard. A smartNIC is a separate device from the NICs on the host machines. In  FIG. 2 , the NVDs  210  and  212  may be implemented as smartNICs that are connected to host machines  202 , and host machines  206  and  208 , respectively. 
     A smartNIC is however just one example of an NVD implementation. Various other implementations are possible. For example, in some other implementations, an NVD or one or more functions performed by the NVD may be incorporated into or performed by one or more host machines, one or more TOR switches, and other components of CSPI  200 . For example, an NVD may be embodied in a host machine where the functions performed by an NVD are performed by the host machine. As another example, an NVD may be part of a TOR switch or a TOR switch may be configured to perform functions performed by an NVD that enables the TOR switch to perform various complex packet transformations that are used for a public cloud. A TOR that performs the functions of an NVD is sometimes referred to as a smart TOR. In yet other implementations, where virtual machines (VMs) instances, but not bare metal (BM) instances, are offered to customers, functions performed by an NVD may be implemented inside a hypervisor of the host machine. In some other implementations, some of the functions of the NVD may be offloaded to a centralized service running on a fleet of host machines. 
     In certain embodiments, such as when implemented as a smartNIC as shown in  FIG. 2 , an NVD may comprise multiple physical ports that enable it to be connected to one or more host machines and to one or more TOR switches. A port on an NVD can be classified as a host-facing port (also referred to as a “south port”) or a network-facing or TOR-facing port (also referred to as a “north port”). A host-facing port of an NVD is a port that is used to connect the NVD to a host machine. Examples of host-facing ports in  FIG. 2  include port  236  on NVD  210 , and ports  248  and  254  on NVD  212 . A network-facing port of an NVD is a port that is used to connect the NVD to a TOR switch. Examples of network-facing ports in  FIG. 2  include port  256  on NVD  210 , and port  258  on NVD  212 . As shown in  FIG. 2 , NVD  210  is connected to TOR switch  214  using link  228  that extends from port  256  of NVD  210  to the TOR switch  214 . Likewise, NVD  212  is connected to TOR switch  216  using link  230  that extends from port  258  of NVD  212  to the TOR switch  216 . 
     An NVD receives packets and frames from a host machine (e.g., packets and frames generated by a compute instance hosted by the host machine) via a host-facing port and, after performing the necessary packet processing, may forward the packets and frames to a TOR switch via a network-facing port of the NVD. An NVD may receive packets and frames from a TOR switch via a network-facing port of the NVD and, after performing the necessary packet processing, may forward the packets and frames to a host machine via a host-facing port of the NVD. 
     In certain embodiments, there may be multiple ports and associated links between an NVD and a TOR switch. These ports and links may be aggregated to form a link aggregator group of multiple ports or links (referred to as a LAG). Link aggregation allows multiple physical links between two end-points (e.g., between an NVD and a TOR switch) to be treated as a single logical link. All the physical links in a given LAG may operate in full-duplex mode at the same speed. LAGs help increase the bandwidth and reliability of the connection between two endpoints. If one of the physical links in the LAG goes down, traffic is dynamically and transparently reassigned to one of the other physical links in the LAG. The aggregated physical links deliver higher bandwidth than each individual link. The multiple ports associated with a LAG are treated as a single logical port. Traffic can be load-balanced across the multiple physical links of a LAG. One or more LAGs may be configured between two endpoints. The two endpoints may be between an NVD and a TOR switch, between a host machine and an NVD, and the like. 
     An NVD implements or performs network virtualization functions. These functions are performed by software/firmware executed by the NVD. Examples of network virtualization functions include without limitation: packet encapsulation and de-capsulation functions; functions for creating a VCN network; functions for implementing network policies such as VCN security list (firewall) functionality; functions that facilitate the routing and forwarding of packets to and from compute instances in a VCN; and the like. In certain embodiments, upon receiving a packet, an NVD is configured to execute a packet processing pipeline for processing the packet and determining how the packet is to be forwarded or routed. As part of this packet processing pipeline, the NVD may execute one or more virtual functions associated with the overlay network such as executing VNICs associated with cis in the VCN, executing a Virtual Router (VR) associated with the VCN, the encapsulation and decapsulation of packets to facilitate forwarding or routing in the virtual network, execution of certain gateways (e.g., the Local Peering Gateway), the implementation of Security Lists, Network Security Groups, network address translation (NAT) functionality (e.g., the translation of Public IP to Private IP on a host by host basis), throttling functions, and other functions. 
     In certain embodiments, the packet processing data path in an NVD may comprise multiple packet pipelines, each composed of a series of packet transformation stages. In certain implementations, upon receiving a packet, the packet is parsed and classified to a single pipeline. The packet is then processed in a linear fashion, one stage after another, until the packet is either dropped or sent out over an interface of the NVD. These stages provide basic functional packet processing building blocks (e.g., validating headers, enforcing throttle, inserting new Layer-2 headers, enforcing L4 firewall, VCN encapsulation/decapsulation, etc.) so that new pipelines can be constructed by composing existing stages, and new functionality can be added by creating new stages and inserting them into existing pipelines. 
     An NVD may perform both control plane and data plane functions corresponding to a control plane and a data plane of a VCN. Examples of a VCN Control Plane are also depicted in  FIGS. 11, 12, 13, and 14  (see references  1116 ,  1216 ,  1316 , and  1416 ) and described below. Examples of a VCN Data Plane are depicted in  FIGS. 11, 12, 13, and 14  (see references  1118 ,  1218 ,  1318 , and  1418 ) and described below. The control plane functions include functions used for configuring a network (e.g., setting up routes and route tables, configuring VNICs, etc.) that controls how data is to be forwarded. In certain embodiments, a VCN Control Plane is provided that computes all the overlay-to-substrate mappings centrally and publishes them to the NVDs and to the virtual network edge devices such as various gateways such as the DRG, the SGW, the IGW, etc. Firewall rules may also be published using the same mechanism. In certain embodiments, an NVD only gets the mappings that are relevant for that NVD. The data plane functions include functions for the actual routing/forwarding of a packet based upon configuration set up using control plane. A VCN data plane is implemented by encapsulating the customer&#39;s network packets before they traverse the substrate network. The encapsulation/decapsulation functionality is implemented on the NVDs. In certain embodiments, an NVD is configured to intercept all network packets in and out of host machines and perform network virtualization functions. 
     As indicated above, an NVD executes various virtualization functions including VNICs and VCN VRs. An NVD may execute VNICs associated with the compute instances hosted by one or more host machines connected to the VNIC. For example, as depicted in  FIG. 2 , NVD  210  executes the functionality for VNIC  276  that is associated with compute instance  268  hosted by host machine  202  connected to NVD  210 . As another example, NVD  212  executes VNIC  280  that is associated with bare metal compute instance  272  hosted by host machine  206 , and executes VNIC  284  that is associated with compute instance  274  hosted by host machine  208 . A host machine may host compute instances belonging to different VCNs, which belong to different customers, and the NVD connected to the host machine may execute the VNICs (i.e., execute VNICs-relate functionality) corresponding to the compute instances. 
     An NVD also executes VCN Virtual Routers corresponding to the VCNs of the compute instances. For example, in the embodiment depicted in  FIG. 2 , NVD  210  executes VCN VR  277  corresponding to the VCN to which compute instance  268  belongs. NVD  212  executes one or more VCN VRs  283  corresponding to one or more VCNs to which compute instances hosted by host machines  206  and  208  belong. In certain embodiments, the VCN VR corresponding to that VCN is executed by all the NVDs connected to host machines that host at least one compute instance belonging to that VCN. If a host machine hosts compute instances belonging to different VCNs, an NVD connected to that host machine may execute VCN VRs corresponding to those different VCNs. 
     In addition to VNICs and VCN VRs, an NVD may execute various software (e.g., daemons) and include one or more hardware components that facilitate the various network virtualization functions performed by the NVD. For purposes of simplicity, these various components are grouped together as “packet processing components” shown in  FIG. 2 . For example, NVD  210  comprises packet processing components  286  and NVD  212  comprises packet processing components  288 . For example, the packet processing components for an NVD may include a packet processor that is configured to interact with the NVD&#39;s ports and hardware interfaces to monitor all packets received by and communicated using the NVD and store network information. The network information may, for example, include network flow information identifying different network flows handled by the NVD and per flow information (e.g., per flow statistics). In certain embodiments, network flows information may be stored on a per VNIC basis. The packet processor may perform packet-by-packet manipulations as well as implement stateful NAT and L4 firewall (FW). As another example, the packet processing components may include a replication agent that is configured to replicate information stored by the NVD to one or more different replication target stores. As yet another example, the packet processing components may include a logging agent that is configured to perform logging functions for the NVD. The packet processing components may also include software for monitoring the performance and health of the NVD and, also possibly of monitoring the state and health of other components connected to the NVD. 
       FIG. 1  shows the components of an example virtual or overlay network including a VCN, subnets within the VCN, compute instances deployed on subnets, VNICs associated with the compute instances, a VR for a VCN, and a set of gateways configured for the VCN. The overlay components depicted in  FIG. 1  may be executed or hosted by one or more of the physical components depicted in  FIG. 2 . For example, the compute instances in a VCN may be executed or hosted by one or more host machines depicted in  FIG. 2 . For a compute instance hosted by a host machine, the VNIC associated with that compute instance is typically executed by an NVD connected to that host machine (i.e., the VNIC functionality is provided by the NVD connected to that host machine). The VCN VR function for a VCN is executed by all the NVDs that are connected to host machines hosting or executing the compute instances that are part of that VCN. The gateways associated with a VCN may be executed by one or more different types of NVDs. For example, certain gateways may be executed by smartNICs, while others may be executed by one or more host machines or other implementations of NVDs. 
     As described above, a compute instance in a customer VCN may communicate with various different endpoints, where the endpoints can be within the same subnet as the source compute instance, in a different subnet but within the same VCN as the source compute instance, or with an endpoint that is outside the VCN of the source compute instance. These communications are facilitated using VNICs associated with the compute instances, the VCN VRs, and the gateways associated with the VCNs. 
     For communications between two compute instances on the same subnet in a VCN, the communication is facilitated using VNICs associated with the source and destination compute instances. The source and destination compute instances may be hosted by the same host machine or by different host machines. A packet originating from a source compute instance may be forwarded from a host machine hosting the source compute instance to an NVD connected to that host machine. On the NVD, the packet is processed using a packet processing pipeline, which can include execution of the VNIC associated with the source compute instance. Since the destination endpoint for the packet is within the same subnet, execution of the VNIC associated with the source compute instance results in the packet being forwarded to an NVD executing the VNIC associated with the destination compute instance, which then processes and forwards the packet to the destination compute instance. The VNICs associated with the source and destination compute instances may be executed on the same NVD (e.g., when both the source and destination compute instances are hosted by the same host machine) or on different NVDs (e.g., when the source and destination compute instances are hosted by different host machines connected to different NVDs). The VNICs may use routing/forwarding tables stored by the NVD to determine the next hop for the packet. 
     For a packet to be communicated from a compute instance in a subnet to an endpoint in a different subnet in the same VCN, the packet originating from the source compute instance is communicated from the host machine hosting the source compute instance to the NVD connected to that host machine. On the NVD, the packet is processed using a packet processing pipeline, which can include execution of one or more VNICs, and the VR associated with the VCN. For example, as part of the packet processing pipeline, the NVD executes or invokes functionality corresponding to the VNIC (also referred to as executes the VNIC) associated with source compute instance. The functionality performed by the VNIC may include looking at the VLAN tag on the packet. Since the packet&#39;s destination is outside the subnet, the VCN VR functionality is next invoked and executed by the NVD. The VCN VR then routes the packet to the NVD executing the VNIC associated with the destination compute instance. The VNIC associated with the destination compute instance then processes the packet and forwards the packet to the destination compute instance. The VNICs associated with the source and destination compute instances may be executed on the same NVD (e.g., when both the source and destination compute instances are hosted by the same host machine) or on different NVDs (e.g., when the source and destination compute instances are hosted by different host machines connected to different NVDs). 
     If the destination for the packet is outside the VCN of the source compute instance, then the packet originating from the source compute instance is communicated from the host machine hosting the source compute instance to the NVD connected to that host machine. The NVD executes the VNIC associated with the source compute instance. Since the destination end point of the packet is outside the VCN, the packet is then processed by the VCN VR for that VCN. The NVD invokes the VCN VR functionality, which may result in the packet being forwarded to an NVD executing the appropriate gateway associated with the VCN. For example, if the destination is an endpoint within the customer&#39;s on-premise network, then the packet may be forwarded by the VCN VR to the NVD executing the DRG gateway configured for the VCN. The VCN VR may be executed on the same NVD as the NVD executing the VNIC associated with the source compute instance or by a different NVD. The gateway may be executed by an NVD, which may be a smartNIC, a host machine, or other NVD implementation. The packet is then processed by the gateway and forwarded to a next hop that facilitates communication of the packet to its intended destination endpoint. For example, in the embodiment depicted in  FIG. 2 , a packet originating from compute instance  268  may be communicated from host machine  202  to NVD  210  over link  220  (using NIC  232 ). On NVD  210 , VNIC  276  is invoked since it is the VNIC associated with source compute instance  268 . VNIC  276  is configured to examine the encapsulated information in the packet, and determine a next hop for forwarding the packet with the goal of facilitating communication of the packet to its intended destination endpoint, and then forward the packet to the determined next hop. 
     A compute instance deployed on a VCN can communicate with various different endpoints. These endpoints may include endpoints that are hosted by CSPI  200  and endpoints outside CSPI  200 . Endpoints hosted by CSPI  200  may include instances in the same VCN or other VCNs, which may be the customer&#39;s VCNs, or VCNs not belonging to the customer. Communications between endpoints hosted by CSPI  200  may be performed over physical network  218 . A compute instance may also communicate with endpoints that are not hosted by CSPI  200 , or are outside CSPI  200 . Examples of these endpoints include endpoints within a customer&#39;s on-premise network or data center, or public endpoints accessible over a public network such as the Internet. Communications with endpoints outside CSPI  200  may be performed over public networks (e.g., the Internet) (not shown in  FIG. 2 ) or private networks (not shown in  FIG. 2 ) using various communication protocols. 
     The architecture of CSPI  200  depicted in  FIG. 2  is merely an example and is not intended to be limiting. Variations, alternatives, and modifications are possible in alternative embodiments. For example, in some implementations, CSPI  200  may have more or fewer systems or components than those shown in  FIG. 2 , may combine two or more systems, or may have a different configuration or arrangement of systems. The systems, subsystems, and other components depicted in  FIG. 2  may be implemented in software (e.g., code, instructions, program) executed by one or more processing units (e.g., processors, cores) of the respective systems, using hardware, or combinations thereof. The software may be stored on a non-transitory storage medium (e.g., on a memory device). 
       FIG. 4  depicts connectivity between a host machine and an NVD for providing I/O virtualization for supporting multitenancy according to certain embodiments. As depicted in  FIG. 4 , host machine  402  executes a hypervisor  404  that provides a virtualized environment. Host machine  402  executes two virtual machine instances, VM 1   406  belonging to customer/tenant # 1  and VM 2   408  belonging to customer/tenant # 2 . Host machine  402  comprises a physical NIC  410  that is connected to an NVD  412  via link  414 . Each of the compute instances is attached to a VNIC that is executed by NVD  412 . In the embodiment in  FIG. 4 , VM 1   406  is attached to VNIC-VM 1   420  and VM 2   408  is attached to VNIC-VM 2   422 . 
     As shown in  FIG. 4 , NIC  410  comprises two logical NICs, logical NIC A  416  and logical NIC B  418 . Each virtual machine is attached to and configured to work with its own logical NIC. For example, VM 1   406  is attached to logical NIC A  416  and VM 2   408  is attached to logical NIC B  418 . Even though host machine  402  comprises only one physical NIC  410  that is shared by the multiple tenants, due to the logical NICs, each tenant&#39;s virtual machine believes they have their own host machine and NIC. 
     In certain embodiments, each logical NIC is assigned its own VLAN ID. Thus, a specific VLAN ID is assigned to logical NIC A  416  for Tenant # 1  and a separate VLAN ID is assigned to logical NIC B  418  for Tenant # 2 . When a packet is communicated from VM 1   406 , a tag assigned to Tenant # 1  is attached to the packet by the hypervisor and the packet is then communicated from host machine  402  to NVD  412  over link  414 . In a similar manner, when a packet is communicated from VM 2   408 , a tag assigned to Tenant # 2  is attached to the packet by the hypervisor and the packet is then communicated from host machine  402  to NVD  412  over link  414 . Accordingly, a packet  424  communicated from host machine  402  to NVD  412  has an associated tag  426  that identifies a specific tenant and associated VM. On the NVD, for a packet  424  received from host machine  402 , the tag  426  associated with the packet is used to determine whether the packet is to be processed by VNIC-VM 1   420  or by VNIC-VM 2   422 . The packet is then processed by the corresponding VNIC. The configuration depicted in  FIG. 4  enables each tenant&#39;s compute instance to believe that they own their own host machine and NIC. The setup depicted in  FIG. 4  provides for I/O virtualization for supporting multi-tenancy. 
       FIG. 5  depicts a simplified block diagram of a physical network  500  according to certain embodiments. The embodiment depicted in  FIG. 5  is structured as a Clos network. A Clos network is a particular type of network topology designed to provide connection redundancy while maintaining high bisection bandwidth and maximum resource utilization. A Clos network is a type of non-blocking, multistage or multi-tiered switching network, where the number of stages or tiers can be two, three, four, five, etc. The embodiment depicted in  FIG. 5  is a 3-tiered network comprising tiers 1, 2, and 3. The TOR switches  504  represent Tier-0 switches in the Clos network. One or more NVDs are connected to the TOR switches. Tier-0 switches are also referred to as edge devices of the physical network. The Tier-0 switches are connected to Tier-1 switches, which are also referred to as leaf switches. In the embodiment depicted in  FIG. 5 , a set of “n” Tier-0 TOR switches are connected to a set of “n” Tier-1 switches and together form a pod. Each Tier-0 switch in a pod is interconnected to all the Tier-1 switches in the pod, but there is no connectivity of switches between pods. In certain implementations, two pods are referred to as a block. Each block is served by or connected to a set of “n” Tier-2 switches (sometimes referred to as spine switches). There can be several blocks in the physical network topology. The Tier-2 switches are in turn connected to “n” Tier-3 switches (sometimes referred to as super-spine switches). Communication of packets over physical network  500  is typically performed using one or more Layer-3 communication protocols. Typically, all the layers of the physical network, except for the TORs layer are n-ways redundant thus allowing for high availability. Policies may be specified for pods and blocks to control the visibility of switches to each other in the physical network so as to enable scaling of the physical network. 
     A feature of a Clos network is that the maximum hop count to reach from one Tier-0 switch to another Tier-0 switch (or from an NVD connected to a Tier-0-switch to another NVD connected to a Tier-0 switch) is fixed. For example, in a  3 -Tiered Clos network at most seven hops are needed for a packet to reach from one NVD to another NVD, where the source and target NVDs are connected to the leaf tier of the Clos network. Likewise, in a 4-tiered Clos network, at most nine hops are needed for a packet to reach from one NVD to another NVD, where the source and target NVDs are connected to the leaf tier of the Clos network. Thus, a Clos network architecture maintains consistent latency throughout the network, which is important for communication within and between data centers. A Clos topology scales horizontally and is cost effective. The bandwidth/throughput capacity of the network can be easily increased by adding more switches at the various tiers (e.g., more leaf and spine switches) and by increasing the number of links between the switches at adjacent tiers. 
     In certain embodiments, each resource within CSPI is assigned a unique identifier called a Cloud Identifier (CID). This identifier is included as part of the resource&#39;s information and can be used to manage the resource, for example, via a Console or through APIs. An example syntax for a CID is: 
     ocid1.&lt;RESOURCE TYPE&gt;.&lt;REALM&gt;.[REGION][.FUTURE USE].&lt;UNIQUE ID&gt;
     where,   ocid1: The literal string indicating the version of the CID;   resource type: The type of resource (for example, instance, volume, VCN, subnet, user, group, and so on);   realm: The realm the resource is in. Example values are “c1” for the commercial realm, “c2” for the Government Cloud realm, or “c3” for the Federal Government Cloud realm, etc. Each realm may have its own domain name;   region: The region the resource is in. If the region is not applicable to the resource, this part might be blank;   future use: Reserved for future use.   unique ID: The unique portion of the ID. The format may vary depending on the type of resource or service.   

       FIG. 6  shows a simplified block diagram of a system  600  incorporating an exemplary embodiment using active-standby operation. The system  600  may include a customer virtual cloud network (VCN)  622  having a VCN control plane  618 . A plurality of network virtualization devices (NVDs) may communicate with the VCN control plane  618 . For example, a first NVD  646  may have an IP address of X.1, a second NVD  648  may have an IP address of X.2, and a third NVD  650  may have an IP address of X.3. Each of the first NVD  646 , the second NVD  648 , and the third NVD  650  may execute a version of a virtual router (VR) having a virtual IP (VIP) address of A.1. Each of the first NVD  646 , the second NVD  648 , and the third NVD  650  may use a routing protocol such as border gateway protocol (BGP) or routing information protocol (RIP). 
     Each of the first NVD  646 , the second NVD  648 , and the third NVD  650  may also communicate with a respective compute instance. Although three compute instances are shown in  FIG. 6 , any suitable number of compute instances may be used. Each compute instance may be software running on a physical machine or the physical machine itself. Further, each compute instance may be associated with a service host, and each compute instance may provide the same service. For example, the first NVD  646  may communicate with a first compute instance  634  that is associated with a first service host, the second NVD  648  may communicate with a second compute instance  636  that is associated with a second service host, and the third NVD  650  may communicate with a third compute instance  638  that is associated with a third service host. Each service host may be a bare metal instance having a network card that is connected to the respective NVD. 
     The system  600  shown in  FIG. 6  may also include a fourth NVD  642  having an IP address of Y.1. The fourth NVD  642  may communicate with a client host  630  having an IP address of B.1. Alternatively or in addition, the system  600  may include a fifth NVD  654  that may communicate with a dynamic routing gateway (DRG)  658 . An on premise client host  662  may communicate with the DRG  658  via a connection  668  that may utilize an IPSec VPN or FastConnect. One, some, or all of the NVDs shown in  FIG. 6  may be implemented as a smartNIC or as another implementation as described above. 
     The system  600  shown in  FIG. 6  may use active-standby operation in which one or several compute instances are active at any given time, while one or several other compute instances are in standby mode. For example, the first compute instance  634 , the second compute instance  636 , and the third compute instance  638  may have the same IP address of A.2. However, the route advertised by the first compute instance  634  may be signaled with a higher routing preference, such as a lower BGP Multi Exit Discriminator (MED) value or a shorter BGP Autonomous System (AS) Path Length value, while the routes advertised by the second compute instance  636  and the third compute instance  634  may be signaled with lower routing preferences. This would make the A.2* route of the first compute instance  634  be active, while the A.2** routes of the second compute instance  636  and the third compute instance  638  would be in standby mode. As discussed in further detail below, if the active service host fails, at least one of the routes is withdrawn and the traffic is automatically forwarded to at least one of the remaining standby hosts. 
     The system  600  depicted in  FIG. 6  is merely an example and is not intended to unduly limit the scope of claimed embodiments. Many variations, alternatives, and modifications are possible. For example, in some implementations, the system  600  may have more or fewer systems or components than those shown in  FIG. 6 , may combine two or more systems, or may have a different configuration or arrangement of systems. The systems, subsystems, and other components depicted in  FIG. 6  may be implemented in software (e.g., code, instructions, program) executed by one or more processing units (e.g., processors, cores) of the respective systems, using hardware, or combinations thereof. The software may be stored on a non-transitory storage medium (e.g., on a memory device). 
       FIG. 7  shows a simplified block diagram of a system  700  incorporating an exemplary embodiment using equal cost active-active operation. As used herein, “active-active operation” refers to a mode of operation including at least two simultaneously active routes. The system  700  may include a customer VCN  722  having a VCN control plane  718 . A plurality of NVDs may communicate with the VCN control plane  718 . For example, a first NVD  746  may have an IP address of X.1, a second NVD  748  may have an IP address of X.2, and a third NVD  750  may have an IP address of X.3. Each of the first NVD  746 , the second NVD  748 , and the third NVD  750  may execute a version of a VR having a VIP address of A.1. Each of the first NVD  746 , the second NVD  748 , and the third NVD  750  may use a routing protocol such as BGP or RIP. 
     Each of the first NVD  746 , the second NVD  748 , and the third NVD  750  may also communicate with a respective compute instance. Although three compute instances are shown in  FIG. 7 , any suitable number of compute instances may be used. Each compute instance may be software running on a physical machine or the physical machine itself. Further, each compute instance may be associated with a service host, and each compute instance may provide the same service. For example, the first NVD  746  may communicate with a first compute instance  734  that is associated with a first service host, the second NVD  748  may communicate with a second compute instance  736  that is associated with a second service host, and the third NVD  750  may communicate with a third compute instance  738  that is associated with a third service host. Each service host may be a bare metal instance having a network card that is connected to the respective NVD. 
     The system  700  shown in  FIG. 7  may also include a fourth NVD  742  having an IP address of Y.1. The fourth NVD  742  may communicate with a client host  730  having an IP address of B.1. As discussed in further detail below, the fourth NVD  742  may store a forwarding table  774  that indicates how to distribute a data flow that is sent to the A.2 IP address. One, some, or all of the NVDs shown in  FIG. 7  may be implemented as a smartNIC or as another implementation as described above. 
     The system  700  shown in  FIG. 7  may use equal cost active-active operation in which multiple compute instances are active at any given time. The network forwards the traffic equally to all of the compute instances within the service route. For example, each of the first compute instance  734 , the second compute instance  736 , and the third compute instance  738  may have an IP address of A.2 and an equal cost of 10. As discussed in further detail below, if any of the active service hosts fail, the route is withdrawn and its share of the traffic is automatically forwarded to the remaining hosts. Accordingly, there are now multiple A.2 [10]  routes for the A.2 IP address, and traffic destined for the A.2 IP address is distributed across the various routes described above. 
     The system  700  depicted in  FIG. 7  is merely an example and is not intended to unduly limit the scope of claimed embodiments. Many variations, alternatives, and modifications are possible. For example, in some implementations, the system  700  may have more or fewer systems or components than those shown in  FIG. 7 , may combine two or more systems, or may have a different configuration or arrangement of systems. The systems, subsystems, and other components depicted in  FIG. 7  may be implemented in software (e.g., code, instructions, program) executed by one or more processing units (e.g., processors, cores) of the respective systems, using hardware, or combinations thereof. The software may be stored on a non-transitory storage medium (e.g., on a memory device). 
       FIG. 8  shows a simplified block diagram of a system  800  incorporating an exemplary embodiment using unequal cost active-active operation. The system  800  may include a customer VCN  822  having a VCN control plane  818 . A plurality of NVDs may communicate with the VCN control plane  818 . For example, a first NVD  846  may have an IP address of X.1, a second NVD  848  may have an IP address of X.2, and a third NVD  850  may have an IP address of X.3. Each of the first NVD  846 , the second NVD  848 , and the third NVD  850  may execute a version of a VR having a VIP address of A.1. Each of the first NVD  846 , the second NVD  848 , and the third NVD  850  may use a routing protocol such as BGP or RIP. 
     Each of the first NVD  846 , the second NVD  848 , and the third NVD  850  may also communicate with a respective compute instance. Although three compute instances are shown in  FIG. 8 , any suitable number of compute instances may be used. Each compute instance may be software running on a physical machine or the physical machine itself. Further, each compute instance may be associated with a service host, and each compute instance may provide the same service. For example, the first NVD  846  may communicate with a first compute instance  834  that is associated with a first service host, the second NVD  848  may communicate with a second compute instance  836  that is associated with a second service host, and the third NVD  850  may communicate with a third compute instance  838  that is associated with a third service host. Each service host may be a bare metal instance having a network card that is connected to the respective NVD. 
     The system  800  shown in  FIG. 8  may also include a fourth NVD  842  having an IP address of Y.1. The fourth NVD  842  may communicate with a client host  830  having an IP address of B.1. As discussed in further detail below, the fourth NVD  842  may store a forwarding table  874  that indicates how to distribute a data flow that is sent to the A.2 IP address. One, some, or all of the NVDs shown in  FIG. 8  may be implemented as a smartNIC or as another implementation as described above. 
     The system  800  shown in  FIG. 8  may use unequal cost active-active operation in which multiple compute instances are active at any given time. The network forwards the traffic according to a cost associated with each of the compute instances within the service route. For example, the first compute instance  834  may have an IP address of A.2 and a cost of 5. Further, the second compute instance  836  may have an IP address of A.2 and a cost of 10. In addition, the third compute instance  838  may have an IP address of A.2 and a cost of 15. As discussed in further detail below, if any of the active service hosts fail, the route is withdrawn and its share of the traffic is automatically distributed among the remaining hosts based on their costs. 
     The system  800  depicted in  FIG. 8  is merely an example and is not intended to unduly limit the scope of claimed embodiments. Many variations, alternatives, and modifications are possible. For example, in some implementations, the system  800  may have more or fewer systems or components than those shown in  FIG. 8 , may combine two or more systems, or may have a different configuration or arrangement of systems. The systems, subsystems, and other components depicted in  FIG. 8  may be implemented in software (e.g., code, instructions, program) executed by one or more processing units (e.g., processors, cores) of the respective systems, using hardware, or combinations thereof. The software may be stored on a non-transitory storage medium (e.g., on a memory device). 
       FIG. 9  shows a simplified flowchart  900  depicting processing to establish or modify a forwarding table for distributing data flows among compute instances according to certain embodiments. The processing depicted in  FIG. 9  may be implemented in software (e.g., code, instructions, program) executed by one or more processing units (e.g., processors, cores) of the respective systems, using hardware, or combinations thereof. The software may be stored on a non-transitory storage medium (e.g., on a memory device). The method presented in  FIG. 9  and described below is intended to be illustrative and non-limiting. Although  FIG. 9  depicts the various processing steps occurring in a particular sequence or order, this is not intended to be limiting. In certain alternative embodiments, the processing may be performed in some different order or some steps may also be performed in parallel. The method shown in  FIG. 9  may be used to add or drop a compute instance as a potential destination for data flows. 
     As shown in  FIG. 9 , at block  910  a first compute instance may advertise first information to a first NVD of a plurality of NVDs. For example, for the embodiment depicted in  FIG. 6 , the first compute instance  634  may advertise first information to the first NVD  646 . In this example, the first information may include the IP address A.2 of the first compute instance  634 , along with the status indicator, shown in  FIG. 6  as “*”, of the first compute instance  634 , which status indicator indicates the route to the first compute instance  634  as active. Similarly, for the embodiment depicted in  FIG. 7 , the first compute instance  734  may advertise first information to the first NVD  746 . In this example, the first information may include the IP address A.2 of the first compute instance  734 , along with the cost of  10  of the first compute instance  734 . Likewise, for the embodiment depicted in  FIG. 8 , the first compute instance  834  may advertise first information to the first NVD  846 . In this example, the first information may include the IP address A.2 of the first compute instance  834 , along with the cost of 5 of the first compute instance  834 . In addition, some or all of the other compute instances within the system may advertise their information to a respective NVD. For example, for the embodiment depicted in  FIG. 6 , the second compute instance  636  may advertise its second information to the second NVD  648 , and/or the third compute instance  638  may advertise its third information to the third NVD  650 . In other embodiments, the advertisement of the first information may be the absence of a keep-alive signal from the first compute instance. For example, each compute instance may send a keep-alive signal to the respective NVD at predetermined intervals, and may advertise that it is no longer active by failing to send the keep-alive signal. 
     At block  915  the first NVD may send a communication with the first information to a VCN control plane. The first NVD may use various routing protocols. For example, the first NVD may use an open routing protocol such as BGP or RIP. Alternatively, the first NVD may use a proprietary routing protocol. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may send a communication with the first information provided by the first compute instance  634  to the VCN control plane  618 . In addition, some or all of the other NVDs within the system may send the information about the respective compute instances to the VCN control plane. For example, for the embodiment depicted in  FIG. 6 , the second NVD  648  may send a communication with the second information provided by the second compute instance  636  to the VCN control plane  618 , and/or the third NVD  650  may send a communication with the third information provided by the third compute instance  638  to the VCN control plane  618 . 
     At block  920  the VCN control plane may receive the communication from the first NVD. For example, for the embodiment depicted in  FIG. 6 , the VCN control plane  618  may receive the communication with the first information provided by the first compute instance  634  from the first NVD  646 . In addition, the VCN control plane  618  may receive communications from some or all of the other NVDs within the system. For example, for the embodiment depicted in  FIG. 6 , the VCN control plane  618  may receive the communication with the second information provided by the second compute instance  636  from the second NVD  648 , and/or the VCN control plane  618  may receive the communication with the third information provided by the third compute instance  638  from the third NVD  650 . The first NVD  646 , the second NVD  648 , and the third NVD  650  may advertise the same IP address A.2. More generally, some of all of the NVDs within the system  600  may advertise the same IP address. 
     At block  925  the VCN control plane may aggregate the first information provided by the first compute instance and received from the first NVD with information provided by the other compute instances and received from the other NVDs. The VCN control plane may use this aggregation to generate or update a forwarding table that includes the first information. For example, for the embodiment depicted in  FIG. 6 , the VCN control plane  618  may aggregate the first information provided by the first compute instance  634  and received from the first NVD  646  with the second information provided by the second compute instance  636  and received from the second NVD  648  and/or with the third information provided by the third compute instance  638  and received from the third NVD  650 . In some examples, the VCN control plane  618  may generate a new forwarding table that includes the first information and the information provided by the other compute instances. In other examples, the VCN control plane  618  may modify an existing forwarding table by replacing previous information about the first compute instance  634  with the first information about the first compute instance  634 . The forwarding table  774  shown in  FIG. 7  and the forwarding table  874  shown in  FIG. 8  are examples of the forwarding table that may be generated at block  925 . For example, the forwarding tables  774  and  874  may distribute traffic that is sent to the IP address A.2 to the IP addresses X.1, X.2, and X.3 as discussed in further detail below with reference to  FIG. 10 . 
     At block  930  the VCN control plane may identify a subset of the plurality of NVDs to receive the forwarding table that was produced at block  925 . The subset may include one, some, or all of the NVDs in the system. For example, for the embodiment depicted in  FIG. 6 , the VCN control plane  618  may identify the first NVD  646 , the second NVD  648 , the third NVD  650 , and the fourth NVD  642  to receive the forwarding table. 
     At block  935  the VCN control plane may publish a communication that includes the forwarding table to the subset of the plurality of NVDs that were identified at block  930 . For example, for the embodiment depicted in  FIG. 6 , the VCN control plane  618  may publish a communication that includes the forwarding table to the first NVD  646 , the second NVD  648 , the third NVD  650 , and the fourth NVD  642 . 
     At block  940  each of the subset of the plurality of NVDs that were identified at block  930  may receive the communication from the VCN control plane. Further, each of the subset of the plurality of NVDs may update a forwarding table that is stored on the NVD. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may receive the communication from the VCN control plane  618  and update the forwarding table that is stored on the first NVD  646 . Similarly, the second NVD  648  may receive the communication from the VCN control plane  618  and update the forwarding table that is stored on the second NVD  648 . Likewise, the third NVD  650  may receive the communication from the VCN control plane  618  and update the forwarding table that is stored on the third NVD  650 . Further, the fourth NVD  642  may receive the communication from the VCN control plane  618  and update the forwarding table that is stored on the fourth NVD  642 . 
       FIG. 10  shows a simplified flowchart  1000  depicting processing to distribute data flows among compute instances according to certain embodiments. The processing depicted in  FIG. 10  may be implemented in software (e.g., code, instructions, program) executed by one or more processing units (e.g., processors, cores) of the respective systems, using hardware, or combinations thereof. The software may be stored on a non-transitory storage medium (e.g., on a memory device). The method presented in  FIG. 10  and described below is intended to be illustrative and non-limiting. Although  FIG. 10  depicts the various processing steps occurring in a particular sequence or order, this is not intended to be limiting. In certain alternative embodiments, the processing may be performed in some different order or some steps may also be performed in parallel. 
     As shown in  FIG. 10 , at block  1010  a first NVD may receive a data packet from a client host that is destined for a service host. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may receive a request from the client host  630  to deliver a data packet to a service host that uses the A.1 IP address. The request may be received via a routing protocol such as BGP or RIP. 
     At block  1015  the first NVD may determine the data flow to which the data packet belongs. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may identify a data flow that includes a series of data packets. The data packets within a single data flow may arrive separately. Each data packet may include a header having a source ID, a source port, a destination ID, a destination port, and a protocol. The first NVD  646  may use these components of the header to identify the data flow to which the data packet belongs. 
     At block  1020  the first NVD may identify potential destination compute instances for the data packet from the forwarding table. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may reference the forwarding table that is stored in the first NVD  646  to identify the first compute instance  634 , the second compute instance  636 , and the third compute instance  638  as potential destination compute instances for the data packet. Each of the potential destination compute instances share the common virtual IP address of A.1. Further, the first compute instance  634 , the second compute instance  636 , and the third compute instance  638  may have the same IP address of A.2. However, as discussed above, the route advertised by the first compute instance  634  may be signaled with a higher routing preference, while the routes advertised by the second compute instance  636  and the third compute instance  634  may be signaled with lower routing preferences. Accordingly, the A.2* route of the first compute instance  634  would be active, while the A.2** routes of the second compute instance  636  and the third compute instance  638  would be in standby mode. 
     At block  1025  the first NVD may retrieve a history of data flow transmissions from the client host. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may retrieve a history of the data flow transmissions from the client host  630  to the service hosts that use the A.1 IP address. The history may indicate whether each data flow was transmitted to the first compute instance  634 , the second compute instance  636 , or the third compute instance  638 . 
     At block  1030  the first NVD may select one of the destination compute instances based on the forwarding table and/or the history of data flow transmissions. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may determine whether the data packet is part of a data flow that was previously transmitted to one of the destination compute instances. If so, the first NVD  646  may select the same destination compute instances for transmission of the data packet. If not, the first NVD  646  may refer to the forwarding table to determine the rules for forwarding the data packet. For the embodiment depicted in  FIG. 6 , the first NVD  646  would forward the data packet to the first compute instance  634 , because the first compute instance  634  is active while the second compute instance  636  and the third compute instance  638  are in standby mode. For the embodiment depicted in  FIG. 7 , the first NVD  746  would use an equal cost method to determine whether to forward the data packet to the first compute instance  734 , the second compute instance  736 , or the third compute instance  738 . This may include referencing the history of data flow transmissions to ensure that the data flows are being transmitted equally or approximately equally to the first compute instance  734 , the second compute instance  736 , and the third compute instance  738 . For the embodiment depicted in  FIG. 8 , the first NVD  846  would use an unequal cost method to determine whether to forward the data packet to the first compute instance  834 , the second compute instance  836 , or the third compute instance  838 . This may include referencing the history of data flow transmissions to ensure that the data flows are being transmitted according to the relative costs associated with the first compute instance  834 , the second compute instance  836 , and the third compute instance  838 . For example, because the first compute instance  834  has a cost that is twice as high as the cost of the second compute instance  836 , the first NVD  846  may route twice as many data flows to the second compute instance  836  than to the first compute instance  834 . 
     At block  1035  the first NVD may send the data packet to the selected compute instance. For example, for the embodiment depicted in  FIG. 6 , if the data packet is part of a data flow that was previously transmitted to the second compute instance  636 , the first NVD  646  may send the data packet to the second compute instance  636 . On the other hand, if the data packet is not part of a data flow that was previously transmitted to one of the potential destination compute instances, the first NVD  646  may send the data packet to the first compute instance  634 . 
     At block  1040  the first NVD may store information about the data packet and the selected compute instance in the history of data flow transmissions. For example, for the embodiment depicted in  FIG. 6 , the first NVD  646  may store information about the data packet, such as its header, along with the selected compute instance to which the data packet was sent at block  1035 , in the history of data flow transmissions that was referenced at block  1030 . 
     As noted above, infrastructure as a service (IaaS) is one particular type of cloud computing. IaaS can be configured to provide virtualized computing resources over a public network (e.g., the Internet). In an IaaS model, a cloud computing provider can host the infrastructure components (e.g., servers, storage devices, network nodes (e.g., hardware), deployment software, platform virtualization (e.g., a hypervisor layer), or the like). In some cases, an IaaS provider may also supply a variety of services to accompany those infrastructure components (e.g., billing, monitoring, logging, security, load balancing and clustering, etc.). Thus, as these services may be policy-driven, IaaS users may be able to implement policies to drive load balancing to maintain application availability and performance. 
     In some instances, IaaS customers may access resources and services through a wide area network (WAN), such as the Internet, and can use the cloud provider&#39;s services to install the remaining elements of an application stack. For example, the user can log in to the IaaS platform to create virtual machines (VMs), install operating systems (OSs) on each VM, deploy middleware such as databases, create storage buckets for workloads and backups, and even install enterprise software into that VM. Customers can then use the provider&#39;s services to perform various functions, including balancing network traffic, troubleshooting application issues, monitoring performance, managing disaster recovery, etc. 
     In most cases, a cloud computing model will require the participation of a cloud provider. The cloud provider may, but need not be, a third-party service that specializes in providing (e.g., offering, renting, selling) IaaS. An entity might also opt to deploy a private cloud, becoming its own provider of infrastructure services. 
     In some examples, IaaS deployment is the process of putting a new application, or a new version of an application, onto a prepared application server or the like. It may also include the process of preparing the server (e.g., installing libraries, daemons, etc.). This is often managed by the cloud provider, below the hypervisor layer (e.g., the servers, storage, network hardware, and virtualization). Thus, the customer may be responsible for handling (OS), middleware, and/or application deployment (e.g., on self-service virtual machines (e.g., that can be spun up on demand) or the like. 
     In some examples, IaaS provisioning may refer to acquiring computers or virtual hosts for use, and even installing needed libraries or services on them. In most cases, deployment does not include provisioning, and the provisioning may need to be performed first. 
     In some cases, there are two different problems for IaaS provisioning. First, there is the initial challenge of provisioning the initial set of infrastructure before anything is running. Second, there is the challenge of evolving the existing infrastructure (e.g., adding new services, changing services, removing services, etc.) once everything has been provisioned. In some cases, these two challenges may be addressed by enabling the configuration of the infrastructure to be defined declaratively. In other words, the infrastructure (e.g., what components are needed and how they interact) can be defined by one or more configuration files. Thus, the overall topology of the infrastructure (e.g., what resources depend on which, and how they each work together) can be described declaratively. In some instances, once the topology is defined, a workflow can be generated that creates and/or manages the different components described in the configuration files. 
     In some examples, an infrastructure may have many interconnected elements. For example, there may be one or more virtual private clouds (VPCs) (e.g., a potentially on-demand pool of configurable and/or shared computing resources), also known as a core network. In some examples, there may also be one or more security group rules provisioned to define how the security of the network will be set up and one or more virtual machines (VMs). Other infrastructure elements may also be provisioned, such as a load balancer, a database, or the like. As more and more infrastructure elements are desired and/or added, the infrastructure may incrementally evolve. 
     In some instances, continuous deployment techniques may be employed to enable deployment of infrastructure code across various virtual computing environments. Additionally, the described techniques can enable infrastructure management within these environments. In some examples, service teams can write code that is desired to be deployed to one or more, but often many, different production environments (e.g., across various different geographic locations, sometimes spanning the entire world). However, in some examples, the infrastructure on which the code will be deployed must first be set up. In some instances, the provisioning can be done manually, a provisioning tool may be utilized to provision the resources, and/or deployment tools may be utilized to deploy the code once the infrastructure is provisioned. 
       FIG. 11  is a block diagram  1100  illustrating an example pattern of an IaaS architecture, according to at least one embodiment. Service operators  1102  can be communicatively coupled to a secure host tenancy  1104  that can include a virtual cloud network (VCN)  1106  and a secure host subnet  1108 . In some examples, the service operators  1102  may be using one or more client computing devices, which may be portable handheld devices (e.g., an iPhone®, cellular telephone, an iPad®, computing tablet, a personal digital assistant (PDA)) or wearable devices (e.g., a Google Glass® head mounted display), running software such as Microsoft Windows Mobile®, and/or a variety of mobile operating systems such as iOS, Windows Phone, Android, BlackBerry 8, Palm OS, and the like, and being Internet, e-mail, short message service (SMS), Blackberry®, or other communication protocol enabled. Alternatively, the client computing devices can be general purpose personal computers including, by way of example, personal computers and/or laptop computers running various versions of Microsoft Windows®, Apple Macintosh®, and/or Linux operating systems. The client computing devices can be workstation computers running any of a variety of commercially-available UNIX® or UNIX-like operating systems, including without limitation the variety of GNU/Linux operating systems, such as for example, Google Chrome OS. Alternatively, or in addition, client computing devices may be any other electronic device, such as a thin-client computer, an Internet-enabled gaming system (e.g., a Microsoft Xbox gaming console with or without a Kinect® gesture input device), and/or a personal messaging device, capable of communicating over a network that can access the VCN  1106  and/or the Internet. 
     The VCN  1106  can include a local peering gateway (LPG)  1110  that can be communicatively coupled to a secure shell (SSH) VCN  1112  via an LPG  1110  contained in the SSH VCN  1112 . The SSH VCN  1112  can include an SSH subnet  1114 , and the SSH VCN  1112  can be communicatively coupled to a control plane VCN  1116  via the LPG  1110  contained in the control plane VCN  1116 . Also, the SSH VCN  1112  can be communicatively coupled to a data plane VCN  1118  via an LPG  1110 . The control plane VCN  1116  and the data plane VCN  1118  can be contained in a service tenancy  1119  that can be owned and/or operated by the IaaS provider. 
     The control plane VCN  1116  can include a control plane demilitarized zone (DMZ) tier  1120  that acts as a perimeter network (e.g., portions of a corporate network between the corporate intranet and external networks). The DMZ-based servers may have restricted responsibilities and help keep security breaches contained. Additionally, the DMZ tier  1120  can include one or more load balancer (LB) subnet(s)  1122 , a control plane app tier  1124  that can include app subnet(s)  1126 , a control plane data tier  1128  that can include database (DB) subnet(s)  1130  (e.g., frontend DB subnet(s) and/or backend DB subnet(s)). The LB subnet(s)  1122  contained in the control plane DMZ tier  1120  can be communicatively coupled to the app subnet(s)  1126  contained in the control plane app tier  1124  and an Internet gateway  1134  that can be contained in the control plane VCN  1116 , and the app subnet(s)  1126  can be communicatively coupled to the DB subnet(s)  1130  contained in the control plane data tier  1128  and a service gateway  1136  and a network address translation (NAT) gateway  1138 . The control plane VCN  1116  can include the service gateway  1136  and the NAT gateway  1138 . 
     The control plane VCN  1116  can include a data plane mirror app tier  1140  that can include app subnet(s)  1126 . The app subnet(s)  1126  contained in the data plane mirror app tier  1140  can include a virtual network interface controller (VNIC)  1142  that can execute a compute instance  1144 . The compute instance  1144  can communicatively couple the app subnet(s)  1126  of the data plane mirror app tier  1140  to app subnet(s)  1126  that can be contained in a data plane app tier  1146 . 
     The data plane VCN  1118  can include the data plane app tier  1146 , a data plane DMZ tier  1148 , and a data plane data tier  1150 . The data plane DMZ tier  1148  can include LB subnet(s)  1122  that can be communicatively coupled to the app subnet(s)  1126  of the data plane app tier  1146  and the Internet gateway  1134  of the data plane VCN  1118 . The app subnet(s)  1126  can be communicatively coupled to the service gateway  1136  of the data plane VCN  1118  and the NAT gateway  1138  of the data plane VCN  1118 . The data plane data tier  1150  can also include the DB subnet(s)  1130  that can be communicatively coupled to the app subnet(s)  1126  of the data plane app tier  1146 . 
     The Internet gateway  1134  of the control plane VCN  1116  and of the data plane VCN  1118  can be communicatively coupled to a metadata management service  1152  that can be communicatively coupled to public Internet  1154 . Public Internet  1154  can be communicatively coupled to the NAT gateway  1138  of the control plane VCN  1116  and of the data plane VCN  1118 . The service gateway  1136  of the control plane VCN  1116  and of the data plane VCN  1118  can be communicatively couple to cloud services  1156 . 
     In some examples, the service gateway  1136  of the control plane VCN  1116  or of the data plan VCN  1118  can make application programming interface (API) calls to cloud services  1156  without going through public Internet  1154 . The API calls to cloud services  1156  from the service gateway  1136  can be one-way: the service gateway  1136  can make API calls to cloud services  1156 , and cloud services  1156  can send requested data to the service gateway  1136 . But, cloud services  1156  may not initiate API calls to the service gateway  1136 . 
     In some examples, the secure host tenancy  1104  can be directly connected to the service tenancy  1119 , which may be otherwise isolated. The secure host subnet  1108  can communicate with the SSH subnet  1114  through an LPG  1110  that may enable two-way communication over an otherwise isolated system. Connecting the secure host subnet  1108  to the SSH subnet  1114  may give the secure host subnet  1108  access to other entities within the service tenancy  1119 . 
     The control plane VCN  1116  may allow users of the service tenancy  1119  to set up or otherwise provision desired resources. Desired resources provisioned in the control plane VCN  1116  may be deployed or otherwise used in the data plane VCN  1118 . In some examples, the control plane VCN  1116  can be isolated from the data plane VCN  1118 , and the data plane mirror app tier  1140  of the control plane VCN  1116  can communicate with the data plane app tier  1146  of the data plane VCN  1118  via VNICs  1142  that can be contained in the data plane mirror app tier  1140  and the data plane app tier  1146 . 
     In some examples, users of the system, or customers, can make requests, for example create, read, update, or delete (CRUD) operations, through public Internet  1154  that can communicate the requests to the metadata management service  1152 . The metadata management service  1152  can communicate the request to the control plane VCN  1116  through the Internet gateway  1134 . The request can be received by the LB subnet(s)  1122  contained in the control plane DMZ tier  1120 . The LB subnet(s)  1122  may determine that the request is valid, and in response to this determination, the LB subnet(s)  1122  can transmit the request to app subnet(s)  1126  contained in the control plane app tier  1124 . If the request is validated and requires a call to public Internet  1154 , the call to public Internet  1154  may be transmitted to the NAT gateway  1138  that can make the call to public Internet  1154 . Memory that may be desired to be stored by the request can be stored in the DB subnet(s)  1130 . 
     In some examples, the data plane mirror app tier  1140  can facilitate direct communication between the control plane VCN  1116  and the data plane VCN  1118 . For example, changes, updates, or other suitable modifications to configuration may be desired to be applied to the resources contained in the data plane VCN  1118 . Via a VNIC  1142 , the control plane VCN  1116  can directly communicate with, and can thereby execute the changes, updates, or other suitable modifications to configuration to, resources contained in the data plane VCN  1118 . 
     In some embodiments, the control plane VCN  1116  and the data plane VCN  1118  can be contained in the service tenancy  1119 . In this case, the user, or the customer, of the system may not own or operate either the control plane VCN  1116  or the data plane VCN  1118 . Instead, the IaaS provider may own or operate the control plane VCN  1116  and the data plane VCN  1118 , both of which may be contained in the service tenancy  1119 . This embodiment can enable isolation of networks that may prevent users or customers from interacting with other users&#39;, or other customers&#39;, resources. Also, this embodiment may allow users or customers of the system to store databases privately without needing to rely on public Internet  1154 , which may not have a desired level of security, for storage. 
     In other embodiments, the LB subnet(s)  1122  contained in the control plane VCN  1116  can be configured to receive a signal from the service gateway  1136 . In this embodiment, the control plane VCN  1116  and the data plane VCN  1118  may be configured to be called by a customer of the IaaS provider without calling public Internet  1154 . Customers of the IaaS provider may desire this embodiment since database(s) that the customers use may be controlled by the IaaS provider and may be stored on the service tenancy  1119 , which may be isolated from public Internet  1154 . 
       FIG. 12  is a block diagram  1200  illustrating another example pattern of an IaaS architecture, according to at least one embodiment. Service operators  1202  (e.g. service operators  1102  of  FIG. 11 ) can be communicatively coupled to a secure host tenancy  1204  (e.g. the secure host tenancy  1104  of  FIG. 11 ) that can include a virtual cloud network (VCN)  1206  (e.g. the VCN  1106  of  FIG. 11 ) and a secure host subnet  1208  (e.g. the secure host subnet  1108  of  FIG. 11 ). The VCN  1206  can include a local peering gateway (LPG)  1210  (e.g. the LPG  1110  of  FIG. 11 ) that can be communicatively coupled to a secure shell (SSH) VCN  1212  (e.g. the SSH VCN  1112  of  FIG. 11 ) via an LPG  1110  contained in the SSH VCN  1212 . The SSH VCN  1212  can include an SSH subnet  1214  (e.g. the SSH subnet  1114  of  FIG. 11 ), and the SSH VCN  1212  can be communicatively coupled to a control plane VCN  1216  (e.g. the control plane VCN  1116  of  FIG. 11 ) via an LPG  1210  contained in the control plane VCN  1216 . The control plane VCN  1216  can be contained in a service tenancy  1219  (e.g. the service tenancy  1119  of  FIG. 11 ), and the data plane VCN  1218  (e.g. the data plane VCN  1118  of  FIG. 11 ) can be contained in a customer tenancy  1221  that may be owned or operated by users, or customers, of the system. 
     The control plane VCN  1216  can include a control plane DMZ tier  1220  (e.g. the control plane DMZ tier  1120  of  FIG. 11 ) that can include LB subnet(s)  1222  (e.g. LB subnet(s)  1122  of  FIG. 11 ), a control plane app tier  1224  (e.g. the control plane app tier  1124  of  FIG. 11 ) that can include app subnet(s)  1226  (e.g. app subnet(s)  1126  of  FIG. 11 ), a control plane data tier  1228  (e.g. the control plane data tier  1128  of  FIG. 11 ) that can include database (DB) subnet(s)  1230  (e.g. similar to DB subnet(s)  1130  of  FIG. 11 ). The LB subnet(s)  1222  contained in the control plane DMZ tier  1220  can be communicatively coupled to the app subnet(s)  1226  contained in the control plane app tier  1224  and an Internet gateway  1234  (e.g. the Internet gateway  1134  of  FIG. 11 ) that can be contained in the control plane VCN  1216 , and the app subnet(s)  1226  can be communicatively coupled to the DB subnet(s)  1230  contained in the control plane data tier  1228  and a service gateway  1236  (e.g. the service gateway of  FIG. 11 ) and a network address translation (NAT) gateway  1238  (e.g. the NAT gateway  1138  of  FIG. 11 ). The control plane VCN  1216  can include the service gateway  1236  and the NAT gateway  1238 . 
     The control plane VCN  1216  can include a data plane mirror app tier  1240  (e.g. the data plane mirror app tier  1140  of  FIG. 11 ) that can include app subnet(s)  1226 . The app subnet(s)  1226  contained in the data plane mirror app tier  1240  can include a virtual network interface controller (VNIC)  1242  (e.g. the VNIC of  1142 ) that can execute a compute instance  1244  (e.g. similar to the compute instance  1144  of  FIG. 11 ). The compute instance  1244  can facilitate communication between the app subnet(s)  1226  of the data plane mirror app tier  1240  and the app subnet(s)  1226  that can be contained in a data plane app tier  1246  (e.g. the data plane app tier  1146  of  FIG. 11 ) via the VNIC  1242  contained in the data plane mirror app tier  1240  and the VNIC  1242  contained in the data plan app tier  1246 . 
     The Internet gateway  1234  contained in the control plane VCN  1216  can be communicatively coupled to a metadata management service  1252  (e.g. the metadata management service  1152  of  FIG. 11 ) that can be communicatively coupled to public Internet  1254  (e.g. public Internet  1154  of  FIG. 11 ). Public Internet  1254  can be communicatively coupled to the NAT gateway  1238  contained in the control plane VCN  1216 . The service gateway  1236  contained in the control plane VCN  1216  can be communicatively couple to cloud services  1256  (e.g. cloud services  1156  of  FIG. 11 ). 
     In some examples, the data plane VCN  1218  can be contained in the customer tenancy  1221 . In this case, the IaaS provider may provide the control plane VCN  1216  for each customer, and the IaaS provider may, for each customer, set up a unique compute instance  1244  that is contained in the service tenancy  1219 . Each compute instance  1244  may allow communication between the control plane VCN  1216 , contained in the service tenancy  1219 , and the data plane VCN  1218  that is contained in the customer tenancy  1221 . The compute instance  1244  may allow resources, that are provisioned in the control plane VCN  1216  that is contained in the service tenancy  1219 , to be deployed or otherwise used in the data plane VCN  1218  that is contained in the customer tenancy  1221 . 
     In other examples, the customer of the IaaS provider may have databases that live in the customer tenancy  1221 . In this example, the control plane VCN  1216  can include the data plane mirror app tier  1240  that can include app subnet(s)  1226 . The data plane mirror app tier  1240  can reside in the data plane VCN  1218 , but the data plane mirror app tier  1240  may not live in the data plane VCN  1218 . That is, the data plane mirror app tier  1240  may have access to the customer tenancy  1221 , but the data plane mirror app tier  1240  may not exist in the data plane VCN  1218  or be owned or operated by the customer of the IaaS provider. The data plane mirror app tier  1240  may be configured to make calls to the data plane VCN  1218  but may not be configured to make calls to any entity contained in the control plane VCN  1216 . The customer may desire to deploy or otherwise use resources in the data plane VCN  1218  that are provisioned in the control plane VCN  1216 , and the data plane mirror app tier  1240  can facilitate the desired deployment, or other usage of resources, of the customer. 
     In some embodiments, the customer of the IaaS provider can apply filters to the data plane VCN  1218 . In this embodiment, the customer can determine what the data plane VCN  1218  can access, and the customer may restrict access to public Internet  1254  from the data plane VCN  1218 . The IaaS provider may not be able to apply filters or otherwise control access of the data plane VCN  1218  to any outside networks or databases. Applying filters and controls by the customer onto the data plane VCN  1218 , contained in the customer tenancy  1221 , can help isolate the data plane VCN  1218  from other customers and from public Internet  1254 . 
     In some embodiments, cloud services  1256  can be called by the service gateway  1236  to access services that may not exist on public Internet  1254 , on the control plane VCN  1216 , or on the data plane VCN  1218 . The connection between cloud services  1256  and the control plane VCN  1216  or the data plane VCN  1218  may not be live or continuous. Cloud services  1256  may exist on a different network owned or operated by the IaaS provider. Cloud services  1256  may be configured to receive calls from the service gateway  1236  and may be configured to not receive calls from public Internet  1254 . Some cloud services  1256  may be isolated from other cloud services  1256 , and the control plane VCN  1216  may be isolated from cloud services  1256  that may not be in the same region as the control plane VCN  1216 . For example, the control plane VCN  1216  may be located in “Region  1 ,” and cloud service “Deployment  5 ,” may be located in Region  1  and in “Region  2 .” If a call to Deployment  5  is made by the service gateway  1236  contained in the control plane VCN  1216  located in Region  1 , the call may be transmitted to Deployment  5  in Region  1 . In this example, the control plane VCN  1216 , or Deployment  5  in Region  1 , may not be communicatively coupled to, or otherwise in communication with, Deployment  5  in Region  2 . 
       FIG. 13  is a block diagram  1300  illustrating another example pattern of an IaaS architecture, according to at least one embodiment. Service operators  1302  (e.g. service operators  1102  of  FIG. 11 ) can be communicatively coupled to a secure host tenancy  1304  (e.g. the secure host tenancy  1104  of  FIG. 11 ) that can include a virtual cloud network (VCN)  1306  (e.g. the VCN  1106  of  FIG. 11 ) and a secure host subnet  1308  (e.g. the secure host subnet  1108  of  FIG. 11 ). The VCN  1306  can include an LPG  1310  (e.g. the LPG  1110  of  FIG. 11 ) that can be communicatively coupled to an SSH VCN  1312  (e.g. the SSH VCN  1112  of  FIG. 11 ) via an LPG  1310  contained in the SSH VCN  1312 . The SSH VCN  1312  can include an SSH subnet  1314  (e.g. the SSH subnet  1114  of  FIG. 11 ), and the SSH VCN  1312  can be communicatively coupled to a control plane VCN  1316  (e.g. the control plane VCN  1116  of  FIG. 11 ) via an LPG  1310  contained in the control plane VCN  1316  and to a data plane VCN  1318  (e.g. the data plane  1118  of  FIG. 11 ) via an LPG  1310  contained in the data plane VCN  1318 . The control plane VCN  1316  and the data plane VCN  1318  can be contained in a service tenancy  1319  (e.g. the service tenancy  1119  of  FIG. 11 ). 
     The control plane VCN  1316  can include a control plane DMZ tier  1320  (e.g. the control plane DMZ tier  1120  of  FIG. 11 ) that can include load balancer (LB) subnet(s)  1322  (e.g. LB subnet(s)  1122  of  FIG. 11 ), a control plane app tier  1324  (e.g. the control plane app tier  1124  of  FIG. 11 ) that can include app subnet(s)  1326  (e.g. similar to app subnet(s)  1126  of  FIG. 11 ), a control plane data tier  1328  (e.g. the control plane data tier  1128  of  FIG. 11 ) that can include DB subnet(s)  1330 . The LB subnet(s)  1322  contained in the control plane DMZ tier  1320  can be communicatively coupled to the app subnet(s)  1326  contained in the control plane app tier  1324  and to an Internet gateway  1334  (e.g. the Internet gateway  1134  of  FIG. 11 ) that can be contained in the control plane VCN  1316 , and the app subnet(s)  1326  can be communicatively coupled to the DB subnet(s)  1330  contained in the control plane data tier  1328  and to a service gateway  1336  (e.g. the service gateway of  FIG. 11 ) and a network address translation (NAT) gateway  1338  (e.g. the NAT gateway  1138  of  FIG. 11 ). The control plane VCN  1316  can include the service gateway  1336  and the NAT gateway  1338 . 
     The data plane VCN  1318  can include a data plane app tier  1346  (e.g. the data plane app tier  1146  of  FIG. 11 ), a data plane DMZ tier  1348  (e.g. the data plane DMZ tier  1148  of  FIG. 11 ), and a data plane data tier  1350  (e.g. the data plane data tier  1150  of  FIG. 11 ). The data plane DMZ tier  1348  can include LB subnet(s)  1322  that can be communicatively coupled to trusted app subnet(s)  1360  and untrusted app subnet(s)  1362  of the data plane app tier  1346  and the Internet gateway  1334  contained in the data plane VCN  1318 . The trusted app subnet(s)  1360  can be communicatively coupled to the service gateway  1336  contained in the data plane VCN  1318 , the NAT gateway  1338  contained in the data plane VCN  1318 , and DB subnet(s)  1330  contained in the data plane data tier  1350 . The untrusted app subnet(s)  1362  can be communicatively coupled to the service gateway  1336  contained in the data plane VCN  1318  and DB subnet(s)  1330  contained in the data plane data tier  1350 . The data plane data tier  1350  can include DB subnet(s)  1330  that can be communicatively coupled to the service gateway  1336  contained in the data plane VCN  1318 . 
     The untrusted app subnet(s)  1362  can include one or more primary VNICs  1364 ( 1 )-(N) that can be communicatively coupled to tenant virtual machines (VMs)  1366 ( 1 )-(N). Each tenant VM  1366 ( 1 )-(N) can be communicatively coupled to a respective app subnet  1367 ( 1 )-(N) that can be contained in respective container egress VCNs  1368 ( 1 )-(N) that can be contained in respective customer tenancies  1370 ( 1 )-(N). Respective secondary VNICs  1372 ( 1 )-(N) can facilitate communication between the untrusted app subnet(s)  1362  contained in the data plane VCN  1318  and the app subnet contained in the container egress VCNs  1368 ( 1 )-(N). Each container egress VCNs  1368 ( 1 )-(N) can include a NAT gateway  1338  that can be communicatively coupled to public Internet  1354  (e.g. public Internet  1154  of  FIG. 11 ). 
     The Internet gateway  1334  contained in the control plane VCN  1316  and contained in the data plane VCN  1318  can be communicatively coupled to a metadata management service  1352  (e.g. the metadata management system  1152  of  FIG. 11 ) that can be communicatively coupled to public Internet  1354 . Public Internet  1354  can be communicatively coupled to the NAT gateway  1338  contained in the control plane VCN  1316  and contained in the data plane VCN  1318 . The service gateway  1336  contained in the control plane VCN  1316  and contained in the data plane VCN  1318  can be communicatively couple to cloud services  1356 . 
     In some embodiments, the data plane VCN  1318  can be integrated with customer tenancies  1370 . This integration can be useful or desirable for customers of the IaaS provider in some cases such as a case that may desire support when executing code. The customer may provide code to run that may be destructive, may communicate with other customer resources, or may otherwise cause undesirable effects. In response to this, the IaaS provider may determine whether to run code given to the IaaS provider by the customer. 
     In some examples, the customer of the IaaS provider may grant temporary network access to the IaaS provider and request a function to be attached to the data plane tier app  1346 . Code to run the function may be executed in the VMs  1366 ( 1 )-(N), and the code may not be configured to run anywhere else on the data plane VCN  1318 . Each VM  1366 ( 1 )-(N) may be connected to one customer tenancy  1370 . Respective containers  1371 ( 1 )-(N) contained in the VMs  1366 ( 1 )-(N) may be configured to run the code. In this case, there can be a dual isolation (e.g., the containers  1371 ( 1 )-(N) running code, where the containers  1371 ( 1 )-(N) may be contained in at least the VM  1366 ( 1 )-(N) that are contained in the untrusted app subnet(s)  1362 ), which may help prevent incorrect or otherwise undesirable code from damaging the network of the IaaS provider or from damaging a network of a different customer. The containers  1371 ( 1 )-(N) may be communicatively coupled to the customer tenancy  1370  and may be configured to transmit or receive data from the customer tenancy  1370 . The containers  1371 ( 1 )-(N) may not be configured to transmit or receive data from any other entity in the data plane VCN  1318 . Upon completion of running the code, the IaaS provider may kill or otherwise dispose of the containers  1371 ( 1 )-(N). 
     In some embodiments, the trusted app subnet(s)  1360  may run code that may be owned or operated by the IaaS provider. In this embodiment, the trusted app subnet(s)  1360  may be communicatively coupled to the DB subnet(s)  1330  and be configured to execute CRUD operations in the DB subnet(s)  1330 . The untrusted app subnet(s)  1362  may be communicatively coupled to the DB subnet(s)  1330 , but in this embodiment, the untrusted app subnet(s) may be configured to execute read operations in the DB subnet(s)  1330 . The containers  1371 ( 1 )-(N) that can be contained in the VM  1366 ( 1 )-(N) of each customer and that may run code from the customer may not be communicatively coupled with the DB subnet(s)  1330 . 
     In other embodiments, the control plane VCN  1316  and the data plane VCN  1318  may not be directly communicatively coupled. In this embodiment, there may be no direct communication between the control plane VCN  1316  and the data plane VCN  1318 . However, communication can occur indirectly through at least one method. An LPG  1310  may be established by the IaaS provider that can facilitate communication between the control plane VCN  1316  and the data plane VCN  1318 . In another example, the control plane VCN  1316  or the data plane VCN  1318  can make a call to cloud services  1356  via the service gateway  1336 . For example, a call to cloud services  1356  from the control plane VCN  1316  can include a request for a service that can communicate with the data plane VCN  1318 . 
       FIG. 14  is a block diagram  1400  illustrating another example pattern of an IaaS architecture, according to at least one embodiment. Service operators  1402  (e.g. service operators  1102  of  FIG. 11 ) can be communicatively coupled to a secure host tenancy  1404  (e.g. the secure host tenancy  1104  of  FIG. 11 ) that can include a virtual cloud network (VCN)  1406  (e.g. the VCN  1106  of  FIG. 11 ) and a secure host subnet  1408  (e.g. the secure host subnet  1108  of  FIG. 11 ). The VCN  1406  can include an LPG  1410  (e.g. the LPG  1110  of  FIG. 11 ) that can be communicatively coupled to an SSH VCN  1412  (e.g. the SSH VCN  1112  of  FIG. 11 ) via an LPG  1410  contained in the SSH VCN  1412 . The SSH VCN  1412  can include an SSH subnet  1414  (e.g. the SSH subnet  1114  of  FIG. 11 ), and the SSH VCN  1412  can be communicatively coupled to a control plane VCN  1416  (e.g. the control plane VCN  1116  of  FIG. 11 ) via an LPG  1410  contained in the control plane VCN  1416  and to a data plane VCN  1418  (e.g. the data plane  1118  of  FIG. 11 ) via an LPG  1410  contained in the data plane VCN  1418 . The control plane VCN  1416  and the data plane VCN  1418  can be contained in a service tenancy  1419  (e.g. the service tenancy  1119  of  FIG. 11 ). 
     The control plane VCN  1416  can include a control plane DMZ tier  1420  (e.g. the control plane DMZ tier  1120  of  FIG. 11 ) that can include LB subnet(s)  1422  (e.g. LB subnet(s)  1122  of  FIG. 11 ), a control plane app tier  1424  (e.g. the control plane app tier  1124  of  FIG. 11 ) that can include app subnet(s)  1426  (e.g. app subnet(s)  1126  of  FIG. 11 ), a control plane data tier  1428  (e.g. the control plane data tier  1128  of  FIG. 11 ) that can include DB subnet(s)  1430  (e.g. DB subnet(s)  1330  of  FIG. 13 ). The LB subnet(s)  1422  contained in the control plane DMZ tier  1420  can be communicatively coupled to the app subnet(s)  1426  contained in the control plane app tier  1424  and to an Internet gateway  1434  (e.g. the Internet gateway  1134  of  FIG. 11 ) that can be contained in the control plane VCN  1416 , and the app subnet(s)  1426  can be communicatively coupled to the DB subnet(s)  1430  contained in the control plane data tier  1428  and to a service gateway  1436  (e.g. the service gateway of  FIG. 11 ) and a network address translation (NAT) gateway  1438  (e.g. the NAT gateway  1138  of  FIG. 11 ). The control plane VCN  1416  can include the service gateway  1436  and the NAT gateway  1438 . 
     The data plane VCN  1418  can include a data plane app tier  1446  (e.g. the data plane app tier  1146  of  FIG. 11 ), a data plane DMZ tier  1448  (e.g. the data plane DMZ tier  1148  of  FIG. 11 ), and a data plane data tier  1450  (e.g. the data plane data tier  1150  of  FIG. 11 ). The data plane DMZ tier  1448  can include LB subnet(s)  1422  that can be communicatively coupled to trusted app subnet(s)  1460  (e.g. trusted app subnet(s)  1360  of  FIG. 13 ) and untrusted app subnet(s)  1462  (e.g. untrusted app subnet(s)  1362  of  FIG. 13 ) of the data plane app tier  1446  and the Internet gateway  1434  contained in the data plane VCN  1418 . The trusted app subnet(s)  1460  can be communicatively coupled to the service gateway  1436  contained in the data plane VCN  1418 , the NAT gateway  1438  contained in the data plane VCN  1418 , and DB subnet(s)  1430  contained in the data plane data tier  1450 . The untrusted app subnet(s)  1462  can be communicatively coupled to the service gateway  1436  contained in the data plane VCN  1418  and DB subnet(s)  1430  contained in the data plane data tier  1450 . The data plane data tier  1450  can include DB subnet(s)  1430  that can be communicatively coupled to the service gateway  1436  contained in the data plane VCN  1418 . 
     The untrusted app subnet(s)  1462  can include primary VNICs  1464 ( 1 )-(N) that can be communicatively coupled to tenant virtual machines (VMs)  1466 ( 1 )-(N) residing within the untrusted app subnet(s)  1462 . Each tenant VM  1466 ( 1 )-(N) can run code in a respective container  1467 ( 1 )-(N), and be communicatively coupled to an app subnet  1426  that can be contained in a data plane app tier  1446  that can be contained in a container egress VCN  1468 . Respective secondary VNICs  1472 ( 1 )-(N) can facilitate communication between the untrusted app subnet(s)  1462  contained in the data plane VCN  1418  and the app subnet contained in the container egress VCN  1468 . The container egress VCN can include a NAT gateway  1438  that can be communicatively coupled to public Internet  1454  (e.g. public Internet  1154  of  FIG. 11 ). 
     The Internet gateway  1434  contained in the control plane VCN  1416  and contained in the data plane VCN  1418  can be communicatively coupled to a metadata management service  1452  (e.g. the metadata management system  1152  of  FIG. 11 ) that can be communicatively coupled to public Internet  1454 . Public Internet  1454  can be communicatively coupled to the NAT gateway  1438  contained in the control plane VCN  1416  and contained in the data plane VCN  1418 . The service gateway  1436  contained in the control plane VCN  1416  and contained in the data plane VCN  1418  can be communicatively couple to cloud services  1456 . 
     In some examples, the pattern illustrated by the architecture of block diagram  1400  of  FIG. 14  may be considered an exception to the pattern illustrated by the architecture of block diagram  1300  of  FIG. 13  and may be desirable for a customer of the IaaS provider if the IaaS provider cannot directly communicate with the customer (e.g., a disconnected region). The respective containers  1467 ( 1 )-(N) that are contained in the VMs  1466 ( 1 )-(N) for each customer can be accessed in real-time by the customer. The containers  1467 ( 1 )-(N) may be configured to make calls to respective secondary VNICs  1472 ( 1 )-(N) contained in app subnet(s)  1426  of the data plane app tier  1446  that can be contained in the container egress VCN  1468 . The secondary VNICs  1472 ( 1 )-(N) can transmit the calls to the NAT gateway  1438  that may transmit the calls to public Internet  1454 . In this example, the containers  1467 ( 1 )-(N) that can be accessed in real-time by the customer can be isolated from the control plane VCN  1416  and can be isolated from other entities contained in the data plane VCN  1418 . The containers  1467 ( 1 )-(N) may also be isolated from resources from other customers. 
     In other examples, the customer can use the containers  1467 ( 1 )-(N) to call cloud services  1456 . In this example, the customer may run code in the containers  1467 ( 1 )-(N) that requests a service from cloud services  1456 . The containers  1467 ( 1 )-(N) can transmit this request to the secondary VNICs  1472 ( 1 )-(N) that can transmit the request to the NAT gateway that can transmit the request to public Internet  1454 . Public Internet  1454  can transmit the request to LB subnet(s)  1422  contained in the control plane VCN  1416  via the Internet gateway  1434 . In response to determining the request is valid, the LB subnet(s) can transmit the request to app subnet(s)  1426  that can transmit the request to cloud services  1456  via the service gateway  1436 . 
     It should be appreciated that IaaS architectures  1100 ,  1200 ,  1300 ,  1400  depicted in the figures may have other components than those depicted. Further, the embodiments shown in the figures are only some examples of a cloud infrastructure system that may incorporate an embodiment of the disclosure. In some other embodiments, the IaaS systems may have more or fewer components than shown in the figures, may combine two or more components, or may have a different configuration or arrangement of components. 
     In certain embodiments, the IaaS systems described herein may include a suite of applications, middleware, and database service offerings that are delivered to a customer in a self-service, subscription-based, elastically scalable, reliable, highly available, and secure manner. An example of such an IaaS system is the Oracle Cloud Infrastructure (OCI) provided by the present assignee. 
       FIG. 15  illustrates an example computer system  1500 , in which various embodiments of the present disclosure may be implemented. The system  1500  may be used to implement any of the computer systems described above. As shown in the figure, computer system  1500  includes a processing unit  1504  that communicates with a number of peripheral subsystems via a bus subsystem  1502 . These peripheral subsystems may include a processing acceleration unit  1506 , an I/O subsystem  1508 , a storage subsystem  1518  and a communications subsystem  1524 . Storage subsystem  1518  includes tangible computer-readable storage media  1522  and a system memory  1510 . 
     Bus subsystem  1502  provides a mechanism for letting the various components and subsystems of computer system  1500  communicate with each other as intended. Although bus subsystem  1502  is shown schematically as a single bus, alternative embodiments of the bus subsystem may utilize multiple buses. Bus subsystem  1502  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. For example, such architectures may include an Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus, which can be implemented as a Mezzanine bus manufactured to the IEEE P1386.1 standard. 
     Processing unit  1504 , which can be implemented as one or more integrated circuits (e.g., a conventional microprocessor or microcontroller), controls the operation of computer system  1500 . One or more processors may be included in processing unit  1504 . These processors may include single core or multicore processors. In certain embodiments, processing unit  1504  may be implemented as one or more independent processing units  1532  and/or  1534  with single or multicore processors included in each processing unit. In other embodiments, processing unit  1504  may also be implemented as a quad-core processing unit formed by integrating two dual-core processors into a single chip. 
     In various embodiments, processing unit  1504  can execute a variety of programs in response to program code and can maintain multiple concurrently executing programs or processes. At any given time, some or all of the program code to be executed can be resident in processor(s)  1504  and/or in storage subsystem  1518 . Through suitable programming, processor(s)  1504  can provide various functionalities described above. Computer system  1500  may additionally include a processing acceleration unit  1506 , which can include a digital signal processor (DSP), a special-purpose processor, and/or the like. 
     I/O subsystem  1508  may include user interface input devices and user interface output devices. User interface input devices may include a keyboard, pointing devices such as a mouse or trackball, a touchpad or touch screen incorporated into a display, a scroll wheel, a click wheel, a dial, a button, a switch, a keypad, audio input devices with voice command recognition systems, microphones, and other types of input devices. User interface input devices may include, for example, motion sensing and/or gesture recognition devices such as the Microsoft Kinect® motion sensor that enables users to control and interact with an input device, such as the Microsoft Xbox® 360 game controller, through a natural user interface using gestures and spoken commands. User interface input devices may also include eye gesture recognition devices such as the Google Glass® blink detector that detects eye activity (e.g., ‘blinking’ while taking pictures and/or making a menu selection) from users and transforms the eye gestures as input into an input device (e.g., Google Glass®). Additionally, user interface input devices may include voice recognition sensing devices that enable users to interact with voice recognition systems (e.g., Siri® navigator), through voice commands. 
     User interface input devices may also include, without limitation, three dimensional (3D) mice, joysticks or pointing sticks, gamepads and graphic tablets, and audio/visual devices such as speakers, digital cameras, digital camcorders, portable media players, webcams, image scanners, fingerprint scanners, barcode reader 3D scanners, 3D printers, laser rangefinders, and eye gaze tracking devices. Additionally, user interface input devices may include, for example, medical imaging input devices such as computed tomography, magnetic resonance imaging, position emission tomography, medical ultrasonography devices. User interface input devices may also include, for example, audio input devices such as MIDI keyboards, digital musical instruments and the like. 
     User interface output devices may include a display subsystem, indicator lights, or non-visual displays such as audio output devices, etc. The display subsystem may be a cathode ray tube (CRT), a flat-panel device, such as that using a liquid crystal display (LCD) or plasma display, a projection device, a touch screen, and the like. In general, use of the term “output device” is intended to include all possible types of devices and mechanisms for outputting information from computer system  1500  to a user or other computer. For example, user interface output devices may include, without limitation, a variety of display devices that visually convey text, graphics and audio/video information such as monitors, printers, speakers, headphones, automotive navigation systems, plotters, voice output devices, and modems. 
     Computer system  1500  may comprise a storage subsystem  1518  that comprises software elements, shown as being currently located within a system memory  1510 . System memory  1510  may store program instructions that are loadable and executable on processing unit  1504 , as well as data generated during the execution of these programs. 
     Depending on the configuration and type of computer system  1500 , system memory  1510  may be volatile (such as random access memory (RAM)) and/or non-volatile (such as read-only memory (ROM), flash memory, etc.) The RAM typically contains data and/or program modules that are immediately accessible to and/or presently being operated and executed by processing unit  1504 . In some implementations, system memory  1510  may include multiple different types of memory, such as static random access memory (SRAM) or dynamic random access memory (DRAM). In some implementations, a basic input/output system (BIOS), containing the basic routines that help to transfer information between elements within computer system  1500 , such as during start-up, may typically be stored in the ROM. By way of example, and not limitation, system memory  1510  also illustrates application programs  1512 , which may include client applications, Web browsers, mid-tier applications, relational database management systems (RDBMS), etc., program data  1514 , and an operating system  1516 . By way of example, operating system  1516  may include various versions of Microsoft Windows®, Apple Macintosh®, and/or Linux operating systems, a variety of commercially-available UNIX® or UNIX-like operating systems (including without limitation the variety of GNU/Linux operating systems, the Google Chrome® OS, and the like) and/or mobile operating systems such as iOS, Windows® Phone, Android® OS, BlackBerry® 9 OS, and Palm® OS operating systems. 
     Storage subsystem  1518  may also provide a tangible computer-readable storage medium for storing the basic programming and data constructs that provide the functionality of some embodiments. Software (programs, code modules, instructions) that when executed by a processor provide the functionality described above may be stored in storage subsystem  1518 . These software modules or instructions may be executed by processing unit  1504 . Storage subsystem  1518  may also provide a repository for storing data used in accordance with the present disclosure. 
     Storage subsystem  1500  may also include a computer-readable storage media reader  1520  that can further be connected to computer-readable storage media  1522 . Together and, optionally, in combination with system memory  1510 , computer-readable storage media  1522  may comprehensively represent remote, local, fixed, and/or removable storage devices plus storage media for temporarily and/or more permanently containing, storing, transmitting, and retrieving computer-readable information. 
     Computer-readable storage media  1522  containing code, or portions of code, can also include any appropriate media known or used in the art, including storage media and communication media, such as but not limited to, volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage and/or transmission of information. This can include tangible computer-readable storage media such as RAM, ROM, electronically erasable programmable ROM (EEPROM), flash memory or other memory technology, CD-ROM, digital versatile disk (DVD), or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or other tangible computer readable media. This can also include nontangible computer-readable media, such as data signals, data transmissions, or any other medium which can be used to transmit the desired information and which can be accessed by computing system  1500 . 
     By way of example, computer-readable storage media  1522  may include a hard disk drive that reads from or writes to non-removable, nonvolatile magnetic media, a magnetic disk drive that reads from or writes to a removable, nonvolatile magnetic disk, and an optical disk drive that reads from or writes to a removable, nonvolatile optical disk such as a CD ROM, DVD, and Blu-Ray® disk, or other optical media. Computer-readable storage media  1522  may include, but is not limited to, Zip® drives, flash memory cards, universal serial bus (USB) flash drives, secure digital (SD) cards, DVD disks, digital video tape, and the like. Computer-readable storage media  1522  may also include, solid-state drives (SSD) based on non-volatile memory such as flash-memory based SSDs, enterprise flash drives, solid state ROM, and the like, SSDs based on volatile memory such as solid state RAM, dynamic RAM, static RAM, DRAM-based SSDs, magnetoresistive RAM (MRAM) SSDs, and hybrid SSDs that use a combination of DRAM and flash memory based SSDs. The disk drives and their associated computer-readable media may provide non-volatile storage of computer-readable instructions, data structures, program modules, and other data for computer system  1500 . 
     Communications subsystem  1524  provides an interface to other computer systems and networks. Communications subsystem  1524  serves as an interface for receiving data from and transmitting data to other systems from computer system  1500 . For example, communications subsystem  1524  may enable computer system  1500  to connect to one or more devices via the Internet. In some embodiments communications subsystem  1524  can include radio frequency (RF) transceiver components for accessing wireless voice and/or data networks (e.g., using cellular telephone technology, advanced data network technology, such as 3G, 4G or EDGE (enhanced data rates for global evolution), WiFi (IEEE 802.11 family standards, or other mobile communication technologies, or any combination thereof), global positioning system (GPS) receiver components, and/or other components. In some embodiments communications subsystem  1524  can provide wired network connectivity (e.g., Ethernet) in addition to or instead of a wireless interface. 
     In some embodiments, communications subsystem  1524  may also receive input communication in the form of structured and/or unstructured data feeds  1526 , event streams  1528 , event updates  1530 , and the like on behalf of one or more users who may use computer system  1500 . 
     By way of example, communications subsystem  1524  may be configured to receive data feeds  1526  in real-time from users of social networks and/or other communication services such as Twitter® feeds, Facebook® updates, web feeds such as Rich Site Summary (RSS) feeds, and/or real-time updates from one or more third party information sources. 
     Additionally, communications subsystem  1524  may also be configured to receive data in the form of continuous data streams, which may include event streams  1528  of real-time events and/or event updates  1530 , that may be continuous or unbounded in nature with no explicit end. Examples of applications that generate continuous data may include, for example, sensor data applications, financial tickers, network performance measuring tools (e.g. network monitoring and traffic management applications), clickstream analysis tools, automobile traffic monitoring, and the like. 
     Communications subsystem  1524  may also be configured to output the structured and/or unstructured data feeds  1526 , event streams  1528 , event updates  1530 , and the like to one or more databases that may be in communication with one or more streaming data source computers coupled to computer system  1500 . 
     Computer system  1500  can be one of various types, including a handheld portable device (e.g., an iPhone® cellular phone, an iPad® computing tablet, a PDA), a wearable device (e.g., a Google Glass® head mounted display), a PC, a workstation, a mainframe, a kiosk, a server rack, or any other data processing system. 
     Due to the ever-changing nature of computers and networks, the description of computer system  1500  depicted in the figure is intended only as a specific example. Many other configurations having more or fewer components than the system depicted in the figure are possible. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, firmware, software (including applets), or a combination. Further, connection to other computing devices, such as network input/output devices, may be employed. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will appreciate other ways and/or methods to implement the various embodiments. 
     Although specific embodiments of the disclosure have been described, various modifications, alterations, alternative constructions, and equivalents are also encompassed within the scope of the disclosure. Embodiments of the present disclosure are not restricted to operation within certain specific data processing environments, but are free to operate within a plurality of data processing environments. Additionally, although embodiments of the present disclosure have been described using a particular series of transactions and steps, it should be apparent to those skilled in the art that the scope of the present disclosure is not limited to the described series of transactions and steps. Various features and aspects of the above-described embodiments may be used individually or jointly. 
     Further, while embodiments of the present disclosure have been described using a particular combination of hardware and software, it should be recognized that other combinations of hardware and software are also within the scope of the present disclosure. Embodiments of the present disclosure may be implemented only in hardware, or only in software, or using combinations thereof. The various processes described herein can be implemented on the same processor or different processors in any combination. Accordingly, where components or modules are described as being configured to perform certain operations, such configuration can be accomplished, e.g., by designing electronic circuits to perform the operation, by programming programmable electronic circuits (such as microprocessors) to perform the operation, or any combination thereof. Processes can communicate using a variety of techniques including but not limited to conventional techniques for inter process communication, and different pairs of processes may use different techniques, or the same pair of processes may use different techniques at different times. 
     The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that additions, subtractions, deletions, and other modifications and changes may be made thereunto without departing from the broader spirit and scope as set forth in the claims. Thus, although specific disclosure embodiments have been described, these are not intended to be limiting. Various modifications and equivalents are within the scope of the following claims. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the disclosed embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure. 
     Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is intended to be understood within the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present. 
     Preferred embodiments of this disclosure are described herein, including the best mode known for carrying out the disclosure. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. Those of ordinary skill should be able to employ such variations as appropriate and the disclosure may be practiced otherwise than as specifically described herein. Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     In the foregoing specification, aspects of the disclosure are described with reference to specific embodiments thereof, but those skilled in the art will recognize that the disclosure is not limited thereto. Various features and aspects of the above-described disclosure may be used individually or jointly. Further, embodiments can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive.