Patent Publication Number: US-10776099-B2

Title: Release orchestration for cloud services

Description:
TECHNICAL FIELD 
     One or more implementations relate to the field of updating software; and more specifically, to the updating of software providing cloud services. 
     BACKGROUND ART 
     “Cloud” services provide shared resources, software, and information to computers and other electronic devices upon request. In cloud computing environments, software can be accessible over the internet rather than installed locally on in-house computer systems. Cloud services typically involve over-the-internet provision of dynamically scalable and often virtualized resources. Technological details can be abstracted from the users, who no longer have need for expertise in, or control over, the technology infrastructure “in the cloud” that supports them. 
     The term “micro-services architecture” refers to an architecture in which each of the micro-services does just one thing efficiently and interacts with others of the micro-services as needed. This contrasts with monolithic architectures in which complex software is run on a single, powerful server. Each of the micro-services may use a different type of hardware and/or software to respectively perform a specialized type of processing different from the types of processing performed by the other micro-services. Moreover, the micro-services architecture allows an application to be decomposed into different ones of these smaller micro-services, improving modularity and making the program code easier to understand, design and test. For example, individual micro-services may be modified (e.g., upgraded, swapped out) without affecting the operation of other micro-services used by the application. 
     A container-orchestration system (COS) automates deployment, scaling and management of containerized applications (also referred to as containerized software and containerized apps); in other words, it provides a platform for automating deployment, scaling, and operations of application containers across clusters of hosts. For example, Kubernetes is a COS that works with a range of container tools, including Docker. Another example of a COS is Docker Swarm. A container is a self-contained execution environment, such as a Linux execution environment; in other words, a container is a standard unit of software that packages up code and all its dependencies, so the application runs quickly and reliably from one computing environment to another. A container image is used to create one or more containers at runtime. A container image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings (e.g., a Docker container image becomes a Docker container when it is run on Docker Engine; another container engine is Rkt). 
     With regard to hardware, a COS may include: 1) nodes (also referred to herein as COS nodes), where a node is a representation of a single machine in a COS cluster, where that single machine can be a physical machine in a datacenter or virtual machine hosted on a cloud provider: 2) clusters (also referred to herein as COS clusters), where a cluster represents a more powerful machine resulting from pooling the resources (CPUs and RAM) of the nodes within the cluster; and 3) persistent volumes (a persistent volume is a file system that can be mounted to the cluster, without being associated with any particular node; while traditional local storage associated to each node is treated as a temporary cache to hold programs and data). 
     With regard to software, a COS may include: 1) containers (also referred to as COS containers, Docker containers, etc.); 2) pods (also referred to herein as “replicas,” COS pods,” or “kpods” in a Kubernetes implementation), where a pod is the unit of replication and wraps one or more containers that will share the same resources and local network; 3) deployments, where a deployment manages a pod, including declaring the number of replicas of the pod and monitoring the pods; and 4) ingress, where an ingress refers to a communication channel between a service running in a pod and the outside world, and is typically either an ingress controller, a load balancer, Kube-proxy (a combination of a network proxy and a load balancer). In addition, a COS has support for an abstraction (e.g., a Kubernetes Service) that defines a logical set of pods and a policy by which to access them (sometimes called a micro-service), as well as an API (e.g., Kubernetes Endpoints API) so that the service provided by one of such abstraction can call the service provided by another such abstraction. 
     In operation, a COS cluster of nodes is formed and a set of one or more persistent volumes is attached to that cluster; and a COS deployment is launched onto the cluster, which deployment causes the spinning up of the declared number of COS pods (where spinning up a COS pod includes executing the containerized application(s) specified in the container image(s) identified for that COS pod) and monitors them. 
     A COS typically includes a COS controller to control operation of the COS. A COS controller can receive an operation according to configuration information (sometimes referred to as manifests, an “application programming interface (API) object descriptions,” or “application configuration information”) that describes the desired state of an application in terms of COS constructs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures use like reference numbers to refer to like elements. Although the following figures depict various exemplary implementations, alternative implementations are within the spirit and scope of the appended claims. In the drawings: 
         FIG. 1  is a block diagram illustrating a system for release orchestration of cloud services and a reusable deployment pipeline according to some example implementations. 
         FIG. 2A  is a flow diagram illustrating a method for a system for release orchestration according to some example implementations. 
         FIG. 2B  is a flow diagram illustrating a method for a COS controller and second app version containers according to some example implementations. 
         FIG. 2C  is a flow diagram illustrating a method for a reusable deployment pipeline and an engine according to some example implementations. 
         FIG. 2D  is a flow diagram illustrating a first part of a method for a runlist sequencer and a proxy control plane according to some example implementations. 
         FIG. 2E  is a flow diagram illustrating a second part of a method for a runlist sequencer and a proxy control plane according to some example implementations. 
         FIG. 3A  is a block diagram illustrating an electronic device according to some example implementations. 
         FIG. 3B  is a block diagram of an environment where the above discussed release orchestration technique may be used, according to some implementations. 
     
    
    
     DETAILED DESCRIPTION 
     The following description describes a release orchestration mechanism for cloud services. More specifically, the following description includes descriptions of independent, but combinable, implementations of a system for release orchestration and a reusable deployment pipeline for release orchestration. 
     Exemplary System and Reusable Deployment Pipeline 
       FIG. 1  is a block diagram illustrating a system for release orchestration of cloud services and a reusable deployment pipeline according to some example implementations.  FIG. 1  illustrates a Container Orchestration System (COS)  102  (e.g., Kubernetes, Docker Swarm) to facilitate the communication of production traffic  104  (e.g., via an external virtual internet protocol address (VIP)  106  of the COS  102 ) with a system  100  within the COS  102 . 
     Overview 
     The system  100  controls the release process of updates to an application (app) that runs in COS pods to provide a cloud service(s). For each release of an update to a current version  112 , the system  100  is to: 1) bring up the updated version  132  in new COS pods; 2) control the updating of any underlying state if necessary (e.g., if the service uses a set of one or more database(s)  150 , then update the database(s) as necessary); 3) control a validation of the viability of the updated version  132  through control of an engine  170 ; 4) switch the production traffic  104  from the current version  112  to the updated version  132  (so that the current version  112  and the updated version  132  respectfully become the old version and the current version) if and only after the updated version  132  has been validated (also referred to a pretesting); and 4) gracefully terminate the now old version. 
       FIG. 1  also illustrates a reusable deployment pipeline  180  for release orchestration that is independent of, but combinable with, a system such as the system  100 . In some implementations, the reusable deployment pipeline operates at the application level and causes the validation of the updated application version before production traffic is sent (causes the generation and transmission of test traffic that mimics production traffic, as well as causes the test traffic to be sent to the updated version while the production traffic continues to be sent to the current version) (sometimes referred to as release trust validation), causes the switch to sending production traffic to the updated version (traffic management), and optionally coordinates immediate post-release activities (e.g., database activities such as dropping custom indexes, deleting tables, etc.). 
     In some implementations that use the system  100  and the reusable deployment pipeline  180 , configuration information  122  causes the COS  102  to spin up containers with the updated version  132 , trigger the operation of the reusable deployment pipeline  180  with a set of parameters from the configuration information  122 , and use readiness responses from the updated version  132  to control the shutdown of the containers of the old version (what was formerly the current version  112 ) (including a forced shut down after a time out period as needed) in a manner that provides an opportunity for the old version to finish inflight tasks. The updated version  132  of the app may assist by supporting a mechanism that responds affirmatively to readiness requests from the COS  102  only after the production traffic  104  has been switched to the updated version  132 . 
     Also, for apps that have a stateful database behind them that needs to also be updated to interoperate with the updated version  132 , the updated version  132  may assist by implementing leader election, where the leader causes pre-release database preparation to be performed. The update may also be implemented directly by the reusable deployment pipeline  180 . 
     The reusable deployment pipeline  180  may operate at the application level and cause: 1) a validation of the updated version  132  before production traffic  104  is sent to the updated version  132  (e.g., causes the generation and transmission of test traffic that mimics production traffic, as well as causes the test traffic to be sent to the updated version  132  while the production traffic  104  continues to be sent to the current version  112 ) (sometimes referred to as release trust validation); 2) cause a synchronous or graduated transition to sending the production traffic  104  to the updated version  132  (sometimes referred to as traffic management); and 3) a set of zero or more post-release activities (e.g., database activities such as dropping custom indexes, deleting tables, etc.). In some implementations, the validation is performed by the engine  170  that: 1) operates on demand responsive to the reusable deployment pipeline  180 ; 2) sends test and/or warm up traffic  172  with a header field value that may be used to route that traffic to the updated version  132 ; 3) checks the results of that traffic to determine if the updated version  132  is ready for production traffic; and 4) communicates to the reusable deployment pipeline  180  whether the updated version  132  is validated to receive production traffic. The engine  170  may: perform synthetics monitoring (which may include the running of maintenance related, non-app version specific tests on a schedule, but also allow these test to be done on demand); pre-release, version specific testing (which may include the running of app version specific test on demand—namely, during the release process prior to the transition of production traffic to the updated app version); and/or warmup traffic generation (which may include the generation of traffic intended to reduce the response time of the updated app version after the transition to production traffic). The engine  170  may can be implemented as a one or more units. For instance, when implemented as three separate units they may be referred to as: 1) a synthetics monitor (e.g., Thousand Eyes, App Dynamics); 2) a pre-release, version specific tester; and 3) a warmup traffic generator. 
     The above implementations are advantageous as compared to some conventional systems. For example, a first conventional system using a monolithic application approach (does not use a COS) and update releases have the following drawbacks: 1) validation tests are not run or are run after production traffic is already being sent to the updated version; 2) they require bringing down half the capacity, and thus are scheduled at off-peak hours; 3) they require human interaction and thus do not scale well; 4) production traffic can ping pong between different versions leading to an unsatisfactory service experience; 5) service degradation during the release window is often observable by customers; and 6) in-flight customer activity during a release can be disrupted and transactions fail, especially when the updated version is found to be unstable. 
     A second conventional system uses a COS (e.g., Kubernetes) that has limited support for releasing updates, and it has the following drawbacks: 1) shuts down the old version as the updated version becomes ready, where being “ready” does not include a validation test of the updated version before sending the production traffic; 2) it uses a rolling update model that suffers from some of the same drawbacks described above (e.g., service experience inconsistencies and incorrect behaviors due to ping ponging); and 3) has no built-in traffic director that can be used for traffic routing and switching. 
     Thus, the above implementations are advantageous in that they: 1) allow for validation tests to be run before production traffic is sent to the updated version (thus making it “seamless”); 2) ensure, through a set of threshold numbers in the configuration information  122  as described later herein, a configurable number of the COS pods having the second app version containers  134  be ready before switching the production traffic to the updated version  132 , which configurable number can be set based on a variety of factors (number of the COS pods having the first app version container  114 , expected production traffic volume expected during the release of the updated version) so that the release may be scheduled during peak or off-peak hours; 3) do not require the same level of human interaction and thus scale well; 4) production traffic can be made not to ping pong between different versions (because there is a point in time when the production traffic  104  is switched (see T 2  in  FIG. 1 ), rather than routing production traffic to both versions or a rolling update; 5) allow for the update to be less observable or not observable to customers by avoiding service degradation during the release window; and 6) avoid the disruption of in-flight production traffic and the failure of transactions when the updated version turns out to be unstable during a release. Since releases pose significant risk to a service (See 2.2), the above implementations can scale up efficiently, reduce data center costs, and maintain high trust. 
     Releases can be conducted at any time and are seamless. Implementations may achieve zero-downtime during releases, even when the current and updated versions use different database schema, by relying on the below discussed time windows to maintain data integrity during the periods of version overlap. Furthermore, in addition to release validation and cut over, the above implementations may perform pre-release database preparation and post-release data maintenance actives in those scenarios where the app must query one or more stateful databases when processing traffic. The reusable deployment pipeline enables the release of updates to applications providing cloud services (performs old app version to new app version transition) with trust using containers to enable anytime seamless releases. Thus, the reusable deployment pipeline reduces the time and expense associated with existing techniques for releasing such updates. In one implementation, this is applied to an existing monolith application by containerizing the monolith application and applying the reusable deployment pipeline. 
     Additional Detail 
     Before a time T 2 , the production traffic  104  is being routed by an application (app) aware proxy  108  (e.g., a Layer 7 (also referred to as an L7 or application layer) proxy, which may be implemented using, for example, the open source Envoy Project) to and from (see line  110 ) the current version  112  (also referred to as the first application (app) version) that runs in a number of COS pods having first app version containers  114 . In some implementations, the app aware proxy  108  includes first app version configuration  109  that causes the production traffic  104  to be routed to the current version  112 . The first app version is to be replaced by the orchestrated release of the updated version  132  (also referred to as the second app version). 
     In some implementations, the production traffic  104  causes the application (app) to communicate with the set one or more database(s)  150  (one or more of which may be stateful databases) provided through a database management system (DBMS)  152 . Prior to time T 2 , this communication is with the first app version containers  114  as illustrated by line  154 . In some such implementations, the DBMS  152  is configured with a database username that is assigned to the first app version (illustrated as first app version DB user name  156 ) and a database schema (illustrated as first app version schema  158 ) for accessing data store  160 . In some such implementations, a separate database user name (illustrated as the second app version DB user name  162 ) is assigned (which includes the creating and preloading of a user name if there is not an existing one that can be assigned) to the second app version, and any required database schema for the second app version (illustrated as second app version schema  164 ) is also preloaded, for the second app version to use to access the data store  160 . While some implementations use different database usernames  166  to separate communications from the different app versions, alternative implementations may use another technique (e.g., inclusion of separate identifiers). 
     Container image(s)  140 , including a second app version container image  142 , are registered with a container registry  144  to which the COS controller  126  has access. In some implementations, the container image(s)  140  also include an app aware proxy container image  148  which the COS controller  126  uses to bring up a set of one or more COS pods with app aware proxy containers to implement the app aware proxy  108 . In alternative implementations, the app aware proxy  108  may be deployed independently of the second app version, as it can operate independent of the app functionality. 
     The release process is set in motion by the submission by a release manager  120  (which may be a human and/or an external automated process) of configuration information  122  (also referred to as a manifest) to a deliverer  124  (e.g., a software development platform such as GitHub) for delivery to the COS  102 , and more specifically for delivery to the COS&#39;s controller  126  (also referred to as the controller, the replication controller, the COS controller, and in the case of Kubernetes, the Kubernetes Controller). 
     Responsive to the configuration information  122 , the COS controller is to access the second app version container image  142  through the container registry  144  to bring up (see line  128 ) COS pods having second app version containers  134 . The COS controller  126  is also to send signals (line  128 ; referred to as readiness requests, or readiness probe requests in Kubernetes) to the COS pods having the second app version containers  134  to determine whether and when it can cause the COS pods having the first app version containers  114  to shut down (see line  190 ; which may be done by first instructing each to gracefully shutdown and starting a timer, and then forcing a shutdown of the timer is exceeded). 
     In implementations in which the production traffic  104  causes the application (app) to communicate with the set of one or more database(s)  150 , the second app version container image  142  includes code and database release artifacts (e.g., procedural language/structured query language (PL/SQL) Scripts; database query optimization statistics and/or hints; etc.). The code, when executed within the COS pods having the second app version containers  134 , causes them to participate in the election of a leader (e.g., using an exclusive semaphore), and the elected leader then prepares the database(s)  150  by loading the database release artifacts using the second app version DB user name  162 . In addition, in implementations where the traffic  172  causes the application (app) to communicate with the set of one or more database(s)  150 , the second app version containers  134  communicate with the database(s)  150 . 
     Responsive to the configuration information  122 , the COS controller is also: 1) to cause (see line  129 ) the engine  170  to send test and/or warm up traffic  172  (e.g., communicated via the external virtual internet protocol address (VIP)  106  of the COS  102 ) with an identifier; and 2) to cause the app aware proxy  108  to use that identifier to route the traffic  172  to and from the second app version containers  134  (e.g., see second app version configuration  174 ) while continuing to route the production traffic  104  to and from the first app version containers  114 . Thus, in some implementations, the app being upgraded supports: 1) a mechanism to indicate when the new version of the app is live and can receive test traffic (e.g., supports health mediation signals to such as liveness request (also referred to as liveness probe requests in Kubernetes); and 2) a mechanism to determine when the transition to routing the production traffic to the new version has occurred (e.g., the app pinging a URL to learn if it is receiving production traffic). 
     If and when enough of the COS pods having the second app version containers  134  are live and the second app version has been validated, then the app aware proxy  108  at time T 2  is configured to transition the routing of the production traffic  104  to the second app version containers  134  (see line  176 ). Thus, the production traffic  104  continues to be routed to the current version  112  as the transition to the updated version  132  is in progress. However, if and when it is determined to be safe, the production traffic  104  is switched to the updated version  132 . In the situation where the result of the test traffic  172  indicates that the second app version has one or more problems and cannot be validated, then the switch is not performed and the production traffic  104  continues to be routed to the current version  112 ; since the current version  112  is assumed to be stable, there should be no interruption in the handling of the production traffic  104  due to the failure of the second app version to be validated. This is advantageous over conventional systems which switch production traffic over to the updated version without having performed this type of validation because any unexpected errors can result in the interruption of the processing of the production traffic  104 . Such an interruption would be visible to customers, and therefore result in a less than optimal customer experience. 
     In implementations in which the production traffic  104  causes the application (app) to communicate with the set of one or more database(s)  150 , after the transition that communication is now between the second app version containers  134  and the database(s)  150  (see line  178 ). 
     As previously described, the COS controller  126  is to send signals (line  128 ) to the COS pods having the second app version containers  134  to determine whether and when it can cause the COS pods having the first app version containers  114  to shut down (line  190 ). In some implementations, the second app version container image  142  also includes code, that when executed, causes the COS pods having the second app version containers  134  to: 1) determine whether the transition to sending them the production traffic  104  has occurred; and 2) respond affirmatively to readiness requests from the COS controller  126  only after the transition has occurred (see line  128 ). As compared to conventional systems in which new COS pods would respond to such readiness request irrespective of whether any such validation and transition has occurred, the implementation described herein provides an opportunity for the validation of the updated version  132  to occur by having the COS pods with the second app version containers  134  signal readiness only if and after the validation is successful. 
     Implementations of the reusable deployment pipeline  180  will now be described. In some implementations, the container image(s)  140  also include a reusable deployment pipeline container image(s)  182  which the COS controller  126  uses to bring up a set of one or more COS pods with reusable deployment pipeline containers to implement the reusable deployment pipeline  180 .  FIG. 1  also illustrates implementations in which the reusable deployment pipeline  180  is implemented by or replaced with a runlist sequencer  184  (also referred to as a sequencer or release orchestrater) (e.g., implemented with Rundeck or the open source Jenkins Pipeline project, which offers an end-user programmable pipeline specification language and reliable execution capability) and a proxy control plane  186  (e.g., Switchboard, Istio), in which case the container image(s)  140  may include a runlist sequencer container image  185  and a proxy control plane container image  187  which the COS controller  126  may respectively use to bring up a set of one or more COS pods with runlist sequencer containers to implement the runlist sequencer  184  and a set of one or more COS pods with proxy control plane containers to implement the proxy control plane  186 . While  FIG. 1  illustrates implementations in which the reusable deployment pipeline  180  is implemented by or replaced with a runlist sequencer  184  and a proxy control plane  186 , in other implementations the operations attributed to these are integrated into the COS controller  126 . 
     In some implementations, the runlist sequencer container image  185  includes a parameterized pipeline definition  188  that is controlled through a set of one or more parameters provided in the configuration information  122 . This allows for a greater level of reusability because one or more of the set of parameters may be changed between updates. Thus, responsive to the configuration information  122 , per line  129  the COS controller  126  may also be implemented to determine if there is a reusable deployment pipeline  180  (or runlist sequencer  184 ) already running that can be used; and if not, to bring one up (e.g., bringing up a COS Pod with a runlist sequencer container based on an identification of a runlist sequencer container image  185  in the configuration information  122 ). Further, as described in more detail later herein, the COS controller  126  may provide a set of parameters (e.g., including identification information and/or a threshold number) from the configuration information  122  to the reusable deployment pipeline  180  (or the runlist sequencer  184 ). 
     In some implementations, the runlist sequencer  184  controls the release steps and the proxy control plane  186  controls the set of one or more app aware proxies  108  to route the test traffic and production traffic to the current version  112  and updated version  132 . In some implementations, the runlist sequencer  184 : 1) either fails or succeeds (error outs or completes within a relatively short time); 2) runs in a singleton container alongside the updated version  132  and is active only during releases; 3) is implemented such that each step in the runlist sequencer  184  is idempotent; and/or 4) performs error handling, logs, release robustness, manageability, security etc. 
     When the COS pods having the second app version  134  are brought up, a service discovery service  138  (e.g., Endpoint Discovery Service (EDS) in Envoy, Apache ZooKeeper) found in conventional data centers receives from the COS pods having the second app version containers  134  (see line  137 ) and provides (see line  139 ) to the reusable deployment pipeline  180  (or the proxy control plane  186 ): 1) identification information provided through the COS controller  126  receiving the configuration information  122  and bringing up the COS pods having the Second App Version Containers  134 ; and 2) network information (e.g., IP address(es) and port numbers) for the COS pods having the second app version containers  134 . In addition, the service discovery service  138  recognizes when the COS pods having the first app version containers  114  have been shut down (see line  137 ) and provides notifications of such (see line  139 ) to the reusable deployment pipeline  180  (or the proxy control plane  186 ). 
     The reusable deployment pipeline  180  is to: 1) cause the validation (see line  194 ) of the updated version  132  using the COS pods having the second app version containers  134  that are live (see line  195 ) responsive to receiving from the COS controller  126  a set of parameters (see line  129 ) from the configuration information  122  provided to the COS controller  126 ; 2) if the second app version is validated, to cause a transition to sending the production traffic  104  to the second app version containers that are Live (traffic management) (see line  196 ); and 3) optionally cause post-release activities (e.g., database maintenance activities (see line  197 ) to clean up anything no longer needed since the old app version is no longer being used; sending notifications (see line  198 ) regarding the status (progress and/or success/failure outcomes) of the update to subscribing services  136  (e.g., to trust and internal monitoring systems, to a reliable system of record for further analysis and corrective action). 
     As illustrated by line  199 , the runlist sequencer  184  and the proxy control plane  186  communicate with each other (e.g., the network information for the COS pods having the second app version containers  134 , instructions concerning when to change the routing rules that route the test and/or warmup traffic  172  from the engine  170  and the production traffic  104 , and a notification of when all of the COS pods having the first app version containers  114  have been shut down). The runlist sequencer  184  is to: 1) monitor the status (see line  195 ) of the COS pods having the second app version containers  134 ; 2) instruct (see line  199 ) the proxy control plane  186  when to change the routing rules (see line  196 ) in the app aware proxy  108 ; 3) cause the initiation of and receive the result of (see line  194 ) the test and/or warmup traffic  172 ; and 4) optionally cause any post-release activities (see lines  197  and/or  198 ). 
     In addition to the above, the proxy control plane  186 , only after the transition has occurred, causes the app aware proxy  108  to reply affirmatively to requests (e.g., configure a routing rule) whether the second app version containers  134  are now receiving the production traffic  104 . In some implementations, this is done by causing a URL derived from the identification information in the configuration information  122  to affirmatively respond to pings requesting whether the second app version containers  134  are now receiving the production traffic  104  (according to HTTP, 200=yes and 500=no), wherein code in the second app version container image  142 , when executed, causes the second app version containers  134  to use the same identification information to derive the same URL and to ping it to determine whether the transition has occurred). In other words, in addition to causing the switching of the production traffic  104  to the updated version  132 , around the same time the runlist sequencer  184  also causes the proxy control plane  186  of the app aware proxy  108  to set an indication to indicate that the production traffic  104  is now switched to being sent to the updated version  132 ; the updated version  132 , responsive to this indication, will then respond to readiness requests from the COS controller  126  in the affirmative. This indication mechanism allows for a first window of time within which the test and/or warm up traffic  172  can be sent to the updated version  132  while the production traffic  104  is still being sent to the current version  112 . When the updated version  132  signals ready responsive to requests from the COS controller  126 , the COS controller  126  starts the process of shutting down the COS pods having the first app version containers  114 . As previously described, this shutting down process may include: 1) instructing the COS pods having the first app version containers  114  to gracefully shutdown; and/or 2) using a set of timers to provide a second window of time to allow the COS pods having the first app version containers  114  to have a chance to complete in-flight execution of long running requests and jobs before being forcibly shut down. 
     Thus, the: 1) the first time window is created to delay the COS controller  126  from starting, responsive to the COS pods having the second app version containers  134  reaching a point when they would be considered ready in a conventional system, the shutdown process of the COS pods having the first app version containers  114  so as to provide time for the test and/or warmup traffic  172  to be routed to the updated version  132  while the production traffic  104  is being routed to the current version  112 ; and 2) the second time window is created after cutting over the production traffic  104  from the current version  112  to the updated version  132  so as to provide a reasonable amount of time after the cut over for the current version  112  to process the production traffic  104  that was sent to it. Therefore, there is overlapping execution of the current version  112  and the updated version  132  during the first time window (the current version  112  processing the production traffic  104 , and the updated version  132  processing the test and/or warmup traffic  172 ) and the second time window (the current version  112  processing the production traffic  104  sent to it before the cut over, and the updated version  132  processing the production traffic  104  sent it after the cut over). 
     In some implementations, the app being updated relies on one or more internal services  189  (e.g., a search service, a message queue service, a cache service), and this is addressed by having the first app version containers  114  and the second app version containers  134  communicate separately with these internal services. 
     Also, in some implementations, a construct (referred to herein as a service(s) collection) is used to create, organize, and monitor a set of one or more service(s) to be provided.  FIG. 1  illustrates the option of having multiple service(s) collection by showing service(s) collections  105 A-N. A service(s) collection is a collection of pods (e.g., kpods), and possibly multiple microservices (e.g., Kubernetes services), that each provide one or more service(s). A service(s) collection is a collection in that it: 1) provides multiple instances of the same service and/or microservice through different COS pods; and/or 2) provides different types of services and/or microservices through different COS pods. In some such implementations, the release of the updated version  132  is separately controlled for each such service(s) collection. For example, implementations may support the release of separate configuration information  122  for each service(s) collection  105  by including a service(s) collection ID assigned to each such service(s) collection  105 . Additionally or alternatively, implementations may support multiple COSs  102  in different data centers in different geographic locations, and each of the COS controllers  126  of these COSs  102  may: 1) track the service(s) collections IDs of the service(s) collection they are hosting; and 2) receive a broadcasting of the configuration information  122  for each update to each of the service(s) collection, and decide whether to act on each respective configuration information  122  based on whether the service(s) collection ID in that respective configuration information  122  is one assigned to one of the collection(s) services being hosted by that COS  102 . Additionally or alternatively, different customers (or groups of customers) may be assigned to different (possibly identical) service(s) collections  105 . 
     By way of example, assume that the app being updated provides a customer relationship management (CRM) service (e.g., Sales Cloud by salesforce.com, Inc.), which relies on internal services  189  (e.g., helper microservices that provide a search service, a cache service, and a message queue (MQ) service) and interacts with the database(s)  150 . Also, assume that there may be multiple ones of the service(s) collections  105  that: 1) each include first app version containers, the internal services  189 , and the DBMS  152 ; and 2) provide the CRM service to different customers or groups of customers. For each such service(s) collection, the release manager  120  may submit the configuration information  122  so that the system  100  and/or reusable deployment pipeline  180  attempts to transition that service(s) collection to an updated version of the app (switches to using second app version containers brought up within that service(s) collection). This contrasts with such a CRM service being provided by a self-contained unit (referred to as a Salesforce Point of Deployment (sfPOD) or Salesforce Instance) having all the software and hardware needed to provide the service (e.g., all the application server(s), database server(s), storage, search service etc. and hardware executing them). Thus, while historically the concept of an sfPOD is sometimes thought of as designating physically collocated hardware, each of the service(s) collection  105  can be thought of as a logical sfPOD (also referred to as a logical Salesforce Instance) because the COS  102  is orchestrating the: 1) nodes (also referred to herein as COS nodes), where a node is a representation of a single machine in a COS cluster, where that single machine can be a physical machine in a datacenter or virtual machine hosted on a cloud provider: 2) clusters (also referred to herein as COS clusters  103 ), where a cluster represents a more powerful machine resulting from pooling the resources (CPUs and RAM) of the nodes within the cluster; and 3) persistent volumes (a persistent volume is a file system that can be mounted to the cluster, without being associated with any particular node; while traditional local storage associated to each node is treated as a temporary cache to hold programs and data). 
     Control Signals Summary 
     As described above, some implementations use control signals. In some implementations, these are implemented using HTTP endpoints established using URLs, where the URLs are derived from the IP addresses and port numbers of the second app version containers  134 . The COS controller  126  sends to the COS pods having the second app version containers  134 : 1) liveness requests (e.g., each of the second app version containers  134  establishes an HTTP endpoint with a URL based on IP address:port/ping.jsp, and the COS controller  126  sends liveness probe requests to each of those endpoints until it responds that second app version container is live); and 2) readiness requests (e.g., each of the second app version containers  134  establishes an HTTP endpoint with a URL based on IP address:port/ready.jsp, and the COS controller  126  sends readiness probe requests to each of those endpoints until it responds that the second app version container is ready). 
     The COS pods having the second app version containers  134  each: 1) establish the above described HTTP endpoints; 2) derives an HTTP endpoint with a URL based on identification information (e.g., a service(s) collection ID and/or a second app version ID) in the configuration information, which HTTP endpoint is controlled to indicate whether the transition to sending the production traffic to the updated version  132  has occurred); and 3) responds to readiness requests from the COS controller  126  based on pinging the HTTP endpoint and responding negatively until that HTTP endpoint indicates that the production traffic  104  has be switched to the updated version  132 . 
     The reusable deployment pipeline  180  (or the runlist sequencer  184 ): 1) responsive to receiving the network information for the COS pods having the second app version containers  134  from the service discovery service  138  (in some implementations, via the proxy control plane  186 ), also sends to the COS pods having the second app version containers  134  liveness requests (e.g., as described above, each of the second app version containers  134  establishes an HTTP endpoint with a URL based on IP address:port/ping.jsp, and the COS controller  126  sends liveness probe requests to each of those endpoints until it responds that second app version container is live); 2) receives from the engine  170  a result of the test and/or warmup traffic  172  sent from the engine  170 ; 3) controls an indication of whether the production traffic  104  has been transitioned to the updated version  132  (e.g., cause the establishment and controls the response of an HTTP endpoint with a URL based on identification information (e.g., a service(s) collection ID and/or a second app version ID) in the configuration information to indicate whether the transition to sending the production traffic to the updated version  132  has occurred); and 4) receives notifications from the service discovery service  138  that all the COS pods with the first app version containers  114  have been shut down (in some implementations, via the proxy control plane  186 ). 
     Thus, while the COS controller  126  in conventional systems uses liveness requests to decide whether to restart a COS pod (e.g., it failed to spin up), the liveness requests are being reused for a different purpose by the reusable deployment pipeline  180  (or the runlist sequencer  184 )—as in an input in deciding when to initiate the sending of the test and warmup traffic  172 . Also, while the COS controller  126  in conventional systems may use readiness requests to load balance between the old and new versions during a release window, the reusable deployment pipeline  180  (or the runlist sequencer  184  and the proxy control plane  186 ) and the app aware proxy  108  controls when: 1) the test and/or warm up traffic  172  is to be sent to the updated version  132 ; and 2) when and whether the production traffic  104  is to be sent to the updated version  132 . 
     Exemplary Configuration Information 
     Depending on the implementation, the configuration information  122  may be a declarative description that identifies: 1) the shape of the deployment (number of containers, memory, CPUs etc.) of the updated version  132 ; and 2) a set of parameters for the reusable deployment pipeline  180  (or the parametrized pipeline definition  188  in the runlist sequencer  184 , which pipeline definition identifies the release steps that need to be executed to bring up the updated version  132  and cut over from current version  112  to the updated version  132 ). 
     More specifically, the configuration information  122  may include: 1) an identifier of the second app version container image  142 ; 2) a number of COS pods; 3) the set of parameters including identification information (e.g., a service(s) collection ID and a second app version ID) and a set of one or more threshold numbers); 4) a time period for the second window; 5) optionally DBMS Connection Information for the first app version and the second app version (e.g., database credentials (e.g., Usernames and Passwords) and a database instance name); and 5) optionally an identifier of the reusable deployment pipeline container image(s)  182  (e.g., the runlist sequencer container image  185 ). Table 1 below illustrates exemplary content of the configuration information  122  and how each piece is used by the COS controller  126 , the updated version  132 , and the reusable deployment pipeline  180  (the proxy control plane  186  and the runlist sequencer  184 ). 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 How they are 
                 How they are 
                   
                 How they are 
               
               
                 Items in the 
                 used by the 
                 used by the 
                 How they are used 
                 used by the 
               
               
                 Configuration 
                 COS 
                 Updated Version 
                 by the proxy 
                 runlist sequencer 
               
               
                 Information 122 
                 Controller 126 
                 132 
                 control plane 186 
                 184 
               
               
                   
               
             
            
               
                 Identifier of the 
                 Uses to access 
                 Not used 
                 Not used 
                 Not used 
               
               
                 second app 
                 the container 
                   
                   
                   
               
               
                 version 
                 image to spin 
                   
                   
                   
               
               
                 container image 
                 up 
                   
                   
                   
               
               
                 142 
                   
                   
                   
                   
               
               
                 A number of 
                 Uses to know 
                 Not used 
                 Not used 
                 Not used 
               
               
                 COS pods 
                 how many to 
                   
                   
                   
               
               
                 (replicas) 
                 spin up 
                   
                   
                   
               
               
                 Identification 
                 Provides to the 
                 Provides to the 
                 Provides to the 
                 Part of the set of 
               
               
                 information 
                 updated 
                 service 
                 runlist sequencer 
                 parameters. Uses 
               
               
                 (e.g., a 
                 version 132 
                 discovery 
                 184 along with the 
                 to subscribe to 
               
               
                 service(s) 
                 and the runlist 
                 service 138 for 
                 IP address and 
                 the proxy control 
               
               
                 collection ID 
                 sequencer 
                 delivery to the 
                 port numbers; 
                 plane 186 to 
               
               
                 and a second 
                   
                 proxy control 
                 Uses the IP 
                 receive the IP 
               
               
                 app version ID) 
                   
                 plane 186, along 
                 addresses and port 
                 addresses and 
               
               
                   
                   
                 with IP 
                 numbers to 
                 port numbers of 
               
               
                   
                   
                 addresses and 
                 configure the 
                 the COS pods 
               
               
                   
                   
                 port numbers, of 
                 routing of traffic 
                 having the 
               
               
                   
                   
                 the COS pods 
                 by the app aware 
                 second app 
               
               
                   
                   
                 having the 
                 proxy 108; Uses 
                 to version 
               
               
                   
                   
                 second app 
                 configure and 
                 containers 134 
               
               
                   
                   
                 version 
                 control a routing 
                   
               
               
                   
                   
                 containers 134; 
                 rule in the app 
                   
               
               
                   
                   
                 Uses to derive a 
                 aware proxy 108. 
                   
               
               
                   
                   
                 URL that it 
                 which rule replies 
                   
               
               
                   
                   
                 pings until it 
                 whether the 
                   
               
               
                   
                   
                 indicates that the 
                 updated version 
                   
               
               
                   
                   
                 production 
                 132 is processing 
                   
               
               
                   
                   
                 traffic 104 has 
                 the production 
                   
               
               
                   
                   
                 been switched to 
                 traffic 104 (e,g., 
                   
               
               
                   
                   
                 the updated 
                 uses to cause the 
                   
               
               
                   
                   
                 version 132 
                 derivation of a 
                   
               
               
                   
                   
                   
                 URL and the 
                   
               
               
                   
                   
                   
                 establishment of 
                   
               
               
                   
                   
                   
                 an HTTP endpoint 
                   
               
               
                   
                   
                   
                 for that URL, 
                   
               
               
                   
                   
                   
                 which is 
                   
               
               
                   
                   
                   
                 controlled to 
                   
               
               
                   
                   
                   
                 return 500 or 200 
                   
               
               
                   
                   
                   
                 responsive to an 
                   
               
               
                   
                   
                   
                 HTTP request to 
                   
               
               
                   
                   
                   
                 the URL based on 
                   
               
               
                   
                   
                   
                 whether the 
                   
               
               
                   
                   
                   
                 transition to 
                   
               
               
                   
                   
                   
                 sending the 
                   
               
               
                   
                   
                   
                 production traffic 
                   
               
               
                   
                   
                   
                 104 to the updated 
                   
               
               
                   
                   
                   
                 version 132. has 
                   
               
               
                   
                   
                   
                 occurred) 
                   
               
               
                 A set of one or 
                 Provides to the 
                 Not used 
                 Not used 
                 Part of the set of 
               
               
                 more threshold 
                 runlist 
                   
                   
                 parameters. 
               
               
                 numbers (lower 
                 sequencer 184 
                   
                   
                 Based on the 
               
               
                 if off peak 
                   
                   
                   
                 receipt of the IP 
               
               
                 hours, set 
                   
                   
                   
                 addresses and 
               
               
                 relative to 
                   
                   
                   
                 port numbers, 
               
               
                 number of COS 
                   
                   
                   
                 uses to determine 
               
               
                 pods in the 
                   
                   
                   
                 if enough of the 
               
               
                 deployment) 
                   
                   
                   
                 COS pods having 
               
               
                   
                   
                   
                   
                 the second app 
               
               
                   
                   
                   
                   
                 version 
               
               
                   
                   
                   
                   
                 containers 134 
               
               
                   
                   
                   
                   
                 have been 
               
               
                   
                   
                   
                   
                 brought up to 
               
               
                   
                   
                   
                   
                 start sending 
               
               
                   
                   
                   
                   
                 liveness probes 
               
               
                   
                   
                   
                   
                 requests; Uses to 
               
               
                   
                   
                   
                   
                 determine if 
               
               
                   
                   
                   
                   
                 enough of the 
               
               
                   
                   
                   
                   
                 COS pods having 
               
               
                   
                   
                   
                   
                 the second app 
               
               
                   
                   
                   
                   
                 version 
               
               
                   
                   
                   
                   
                 containers 134 
               
               
                   
                   
                   
                   
                 have responded 
               
               
                   
                   
                   
                   
                 positively to 
               
               
                   
                   
                   
                   
                 liveness probes 
               
               
                   
                   
                   
                   
                 received to 
               
               
                   
                   
                   
                   
                 initiate the 
               
               
                   
                   
                   
                   
                 sending of the 
               
               
                   
                   
                   
                   
                 test and/or warm 
               
               
                   
                   
                   
                   
                 up traffic 172 
               
               
                 An amount of 
                 Uses to 
                 No used 
                 Not used 
                 Not used 
               
               
                 time to wait 
                 provide time 
                   
                   
                   
               
               
                 before a forced 
                 for inflight 
                   
                   
                   
               
               
                 kill of COS pods 
                 tasks to 
                   
                   
                   
               
               
                 having the first 
                 complete 
                   
                   
                   
               
               
                 app version 
                   
                   
                   
                   
               
               
                 containers 114 
                   
                   
                   
                   
               
               
                 Optionally, 
                 Provides the 
                 Uses the DBMS 
                 Not used 
                 Part of the set of 
               
               
                 DBMS 
                 DBMS 
                 Connection 
                   
                 parameters. 
               
               
                 Connection 
                 Connection 
                 Information for 
                   
                 Provides the 
               
               
                 Information for 
                 Information for 
                 the second app 
                   
                 DBMS 
               
               
                 the first app 
                 the second app 
                 version to access 
                   
                 Connection 
               
               
                 version and the 
                 version to the 
                 the database(s) 
                   
                 Information for 
               
               
                 second app 
                 updated 
                 150 
                   
                 the first app 
               
               
                 version (e.g., 
                 version 132; 
                   
                   
                 version and the 
               
               
                 database 
                 Provides the 
                   
                   
                 second app 
               
               
                 credentials (e.g., 
                 DBMS 
                   
                   
                 version for 
               
               
                 Usernames and 
                 connection 
                   
                   
                 database 
               
               
                 Passwords) and 
                 information for 
                   
                   
                 maintenance 
               
               
                 a database 
                 the first app 
                   
                   
                   
               
               
                 instance name); 
                 version and the 
                   
                   
                   
               
               
                   
                 second app 
                   
                   
                   
               
               
                   
                 version to the 
                   
                   
                   
               
               
                   
                 runlist 
                   
                   
                   
               
               
                   
                 sequencer 184 
                   
                   
                   
               
               
                 Optionally an 
                 Compares the 
                 Not used 
                 Not used 
                 Not used 
               
               
                 identifier of the 
                 identifier with 
                   
                   
                   
               
               
                 reusable 
                 the identifier 
                   
                   
                   
               
               
                 deployment 
                 (and in some 
                   
                   
                   
               
               
                 pipeline 
                 cases the set of 
                   
                   
                   
               
               
                 container 
                 parameters) 
                   
                   
                   
               
               
                 image(s) 182 
                 from the prior 
                   
                   
                   
               
               
                   
                 config. info. 
                   
                   
                   
               
               
                   
                 122, and if it 
                   
                   
                   
               
               
                   
                 differs it spins 
                   
                   
                   
               
               
                   
                 up a new 
                   
                   
                   
               
               
                   
                 runlist 
                   
                   
                   
               
               
                   
                 sequencer 184. 
               
               
                   
               
            
           
         
       
     
     Exemplary Operation 
       FIG. 2A  is a flow diagram illustrating a method for a system for release orchestration according to some example implementations. While an app aware proxy routes production traffic to a first application (app) version that runs in a plurality of container orchestration system (COS) pods having first app version containers, receiving in block  200  configuration information including an identification of a second app version container image for a second app version, a number of COS pods, a time period, and a set of parameters including identification information and a threshold number. The second app version is an updated version of the first app version. From block  200 , control passes to block  202 . 
     Block  202  shows, using the second app version container image identified in the configuration information, the bringing up of COS pods having second app version containers until their number meets the number of COS pods from the configuration information. From block  202 , control passes to block  204 . 
     If the first application (app) version is to communicate (query) with a database management system (DBMS) using a database name assigned to the first app version, then: 1) the configuration information includes DBMS connection information for the first app version and the second app version; and 2) optional block  204  shows the preparing of the DBMS by loading app version specific database release artifacts within the second app version container image using the DBMS connection information for the second app version. In some implementations, the DBMS connection information for the second app version was previously preloaded into the DBMS, and the second app version container image was previously registered with the container registry. In some implementations, the DBMS connection information for the first app version and the second app version each include database credentials, which include: 1) database usernames and passwords; and 2) optionally a database instance name. In some implementations, the app version specific database release artifacts include a PL/SQL package and a set or one or more query optimization hints. From block  204 , control passes to block  206 . 
     Block  206  shows that when the threshold number of the COS pods having the second app version containers are live, the causing of a validation of the second app version by causing test and/or warmup traffic to be sent to the COS pods having the second app version containers that are live. In some implementations, this includes causing: 1) the generation and transmission of test traffic that mimics production traffic; and 2) the test traffic to be sent to the second application version while the production traffic continues to be sent to the first application version. From block  206 , control passes to block  208 . 
     In block  208 , it is determined whether the result of the test and/or warmup traffic indicates that the second app version has been validated. If not, control passes to block  210  where appropriate action is taken (e.g., terminating the release of the update and any notifying subscribing services of the failure). Otherwise, control passes to block  212 . 
     Block  212  shows the causing of a transition to sending production traffic to the second app version containers that are live instead of to the first app version. From block  212 , control passes to block  214 . 
     Block  214  shows that the method then starts a set of one or more timers based on the time period indicated in the configuration information and instructs the first app version containers to gracefully shut down. From block  214 , control passes to block  216 . The first app version containers shut down when there is no more work to do (they shut themselves down) or the configured timeout is exceeded. We may configure this timeout in some implementations to be relatively long so that relatively long running work may be completed. 
     In block  216 , if based on expiration of the set of timers, any of the COS pods having the first app version containers that are not yet shut down are forced to shut down. From block  216 , control passes to block  218 . 
     Optional block  218  shows the method causing a set of post-release activities (e.g., database cleanup activities related to the first app version, such as dropping custom indexes, deleting tables, etc.). 
       FIG. 2B  is a flow diagram illustrating a method for a COS controller and second app version containers according to some example implementations. In block  220 , while an app aware proxy routes production traffic to a first application (app) version that runs in a plurality of container orchestration system (COS) pods having first app version containers, the COS controller receives configuration information. From block  220 , control passes to block  221 . 
     Block  221  shows the COS controller bringing up a number of COS pods having second app version containers using a second app version container image and identification information in the configuration information. In some implementations, the second app version container image was previously registered with the container registry. From block  221 , control passes to block  222  and  230 . 
     Optional block  222  shows that when there is not a reusable deployment pipeline already running that can be used, the COS controller brings up a reusable deployment pipeline. In some implementations, this includes the COS controller bringing up a COS pod with a runlist sequencer container based on a runlist sequencer container image identified in the configuration information. From block  222 , control passes to block  223 . 
     Optional block  223  shows the COS controller providing a set of parameters from the configuration information to a reusable deployment pipeline. As previously described, the reusable deployment pipeline is responsible for causing a transition to sending production traffic to the second app version containers instead of the first app version after the second app version containers have been validated. From block  223 , control passes to circled A and block  224 . 
     Block  224  illustrates that the COS controller performs blocks  225 ,  226 ,  227 , and  228  for each of the COS pods having the second app version containers. 
     In block  225 , the COS controller, when the second app version container is live, responds affirmatively to requests from the COS controller determines when the COS pod with the second app version Container is live. In some implementations, this is performed by the COS controller sending to the COS pod with the second app version container liveness requests until the COS pod with the second app version container responds with an indication that it is live. From block  225 , control passes to block  226 . 
     Block  226  shows that after the COS pod having the second app version container is live, determining if and when one of the COS pods with the first app version container can be shut down. In some implementations, this is performed by the COS controller sending to the COS pod with the second app version container readiness requests until a positive indication is returned. From block  226 , control passes to block  227 . 
     In block  227 , when the COS pod with the first app version container is ready to be shut down, the COS controller starts a timer based on a time period indicated in the configuration information and instructs the first app version container to gracefully shut down. From block  227 , control passes to block  228 . 
     In block  228 , the COS controller, when the timer expires, forces the COS pod with the first app version container to shut down if it has not already. 
     If the first application (app) version communicates with a database management system (DBMS), then optional blocks  230  and  231  are performed. Otherwise, control passes from block  221  to block  232 . 
     In optional block  230 , each of the second app version containers participates in choosing of a lead one of the second app version containers. From block  230 , control passes to block  231 . 
     Optional block  231  shows that the lead one of the second app version containers prepares the DBMS by loading second app version specific database release artifacts within the second app version container using the DBMS connection information for the second app version in the configuration information. In some implementations, the DBMS connection information for the second app version was previously preloaded into the DBMS. In some implementations, the DBMS connection information for the first app version and the second app version each include database credentials, which include: 1) database usernames and passwords; and 2) optionally a database instance name. In some implementations, the app version specific database release artifacts include a PL/SQL package and a set of one or more query optimization hints. From block  231 , control passes to block  232 . 
     Block  232  shows that each of the second app version containers, when it is live, responds affirmatively to requests inquiring whether the second app version container is live. Thus, in some implementations block  225  and block  232  illustrate control signals between the COS controller and the second app version containers. From block  232 , control passes to block  233 . 
     In block  233 , each of the second app version containers monitors whether the transition to sending production traffic to the second app version container has occurred. In some implementations, this is performed: 1) deriving a URL based on the identification information (e.g., a services collection identifier and/or a second app version identifier) in the configuration information; and 2) pinging that URL until it indicates that the second app version container is receiving production traffic. Once it has, control passes to block  234  and block  235 . 
     Block  234  shows that responsive to requests from the COS controller as to whether the second app version container is ready, the second app version container responds affirmatively after determining that the transition to sending production traffic to the second app version container has occurred. Thus, in some implementations block  226  and block  234  illustrate control signals between the COS controller and the second app version containers. 
     Optional block  235  shows that each of the second app version containers, after determining that the switch to sending production traffic to the second app version has occurred, starts retrieving tasks from an asynchronous work queue provided by a message queue service. 
       FIG. 2C  is a flow diagram illustrating a method for a reusable deployment pipeline and an engine according to some example implementations. Block  240  shows that, responsive to receiving from a COS controller a set of parameters from configuration information provided to the COS controller while an app aware proxy routes production traffic to a first application (app) version and that runs in container orchestration system (COS) pods having first app version containers, the reusable deployment pipeline causes a validation of a second app version using COS pods having second app version containers that are now live after having been brought up by the COS controller responsive to the provision of the configuration information. The configuration information having been provided to cause a transition to the second app version which is an update to the first app version. From block  240 , control passes to block  242  and  250 . 
     In block  242 , it is determined whether the second app version has been validated. If not, control passes to block  244  where appropriate action is taken (e.g., terminating the release of the update and any notifying subscribing services of the failure). Otherwise, control passes to block  246 . 
     Block  246  shows that after the validation, the reusable deployment pipeline causes the transition to sending production traffic to the second app version containers that are determined to be live instead of to the first app version containers. From block  246 , control passes to block  248 . 
     In optional block  248 , the reusable deployment pipeline causes post-release activities using DBMS connection information for the first app version that was in the configuration information and that was provided through the COS controller. 
     In block  250 , the engine sends test and/or warmup traffic with a value in a header field that an app aware proxy can use to route that traffic to the second app version. Thus, in some implementations block  240  and block  250  illustrate control signals between the reusable deployment pipeline and the engine. From block  250 , control passes to block  252 . 
     Block  252  shows that the engine checks the result of the test and/or warmup traffic to determine whether the second app version is validated to receive production traffic. From block  252 , control passes to block  256 . 
     In block  256 , the engine communicates with the reusable deployment pipeline to indicate whether the second app version is validated for production traffic. 
       FIG. 2D  is a flow diagram illustrating a first part of a method for a runlist sequencer and a proxy control plane according to some example implementations.  FIG. 2D  shows an exploded version of block  240  according to some implementations. 
     In block  260 , the runlist sequencer subscribes, using identification information in the set of parameters, to a proxy control plane to receive network information for the COS pods having the second app version containers. From block  260 , control passes to block  262  and  280 . 
     In block  262 , the runlist sequencer receives from the proxy control plane the network information regarding at least some of the COS pods having the second app version containers. From block  262 , control passes to block  264 . 
     In block  264 , the runlist sequencer determines, using the network information, when a first threshold number of the COS pods having the second app version containers have been brought up by the COS controller. From block  264 , control passes to block  266 . 
     In block  266 , it is determined whether the first threshold number has been met. If not, control passes back to block  262 . Otherwise, control passes to block  268 . 
     In block  268 , the runlist sequencer determines when a second threshold number (which may be the same or different than the first threshold number) of the COS pods having the second app version containers are live. In some implementations, this includes sending liveness requests to each of the COS pods having the second app version containers until that COS pod with the second app version container responds with an indication that it is live. From block  268 , control passes to block  270 . 
     In block  270 , it is determined whether the second threshold number has been met. If not, control passes back to block  268 . Otherwise, control passes to block  272 . 
     In block  272 , the runlist sequencer causes the proxy control plane to configure the app aware proxy with routing rules that distinguish between test traffic and production traffic and that send only the test traffic to those of the second app version containers determined to be live. From block  272 , control passes to block  274  and to block  282 . 
     In block  274 , the runlist sequencer causes the engine to send the test and/or warmup traffic with a value in a header field that the app aware proxy can use to route that traffic to the second app version containers that are live. From block  274 , control passes to block  276 . 
     In block  276 , the runlist sequencer communicates with the engine to determine whether the second app version is validated for production traffic. From block  276 , control passes to block  242 . 
     In block  278 , the proxy control pane receives from a service discovery service both: 1) the identification information provided through the COS controller receiving the configuration information and bringing up the COS pods having the second app version containers; and 2) the network information for the COS pods having the second app version containers. In some embodiments, the network information includes internet protocol (IP) addresses and port numbers for the second app version containers. From block  278 , control passes to block  280 . 
     In block  280 , the proxy control pane sends to the runlist sequencer the network information for the COS pods having the second app version containers. From block  280 , control passes to block  282 . 
     In block  282 , the proxy control pane causes the configuring of the app aware proxy with routing rules that distinguish between test and/or warmup traffic and production traffic and that send only the test and/or warmup traffic to those of the second app version containers determined to be live. This is sometimes referred to as “release awareness.” 
       FIG. 2E  is a flow diagram illustrating a second part of a method for a runlist sequencer and a proxy control plane according to some example implementations.  FIG. 2E  shows an exploded version of block  246  and block  248  according to some implementations. 
     Block  242  includes blocks  290  and  284 . In block  290 , the runlist sequencer causes the proxy control plane to: 1) change the routing rules in the app aware proxy to cause the sending of production traffic to the COS pods having the second app version containers that are live; and 2) cause the app aware proxy to reply affirmatively to requests whether the second app version containers are receiving production traffic. From block  290 , control passes to block  284 . 
     In block  284 , the proxy control plane causes the app aware proxy to: 1) change the routing rules to cause the sending of production traffic to the COS pods having the second app version containers that are live; and 2) reply affirmatively to requests whether the second app version containers are receiving production traffic. In some implementations, this latter operation is performed by switching an HTTP endpoint with a URL derived from identification information (e.g., service(s) collection ID and/or Update App Version ID) in the configuration information to affirmatively respond to pings requesting whether the second app version containers are receiving production traffic (in HTTP, 200=yes and 500=no); and the second app version containers use the same configuration information to derive the same URL and ping that HTTP endpoint). From block  284 , control passes to optional block  248  (and more specifically, to optional block  286  within block  248 ). 
     In block  286 , the proxy control plane, responsive to receiving from the service discovery service notifications reflecting that all the COS pods having the first app version containers are shut down, notifies the runlist sequencer. From block  284 , control passes to optional block  292  within block  248   
     In block  292 , responsive to a notification from proxy control plane that the COS pods having the first app version are all shut down, the runlist sequencer causes post-release activities using DBMS Connection Information for the first app version that was in the configuration information and that was provided through the COS Controller. By way of examples, block  292  may include: 1) causing database cleanup activities (e.g., by triggering a maintenance script in an engine) related to the first app version, such as deleting tables and dropping custom indices (block  294 ); and 2) sending notifications regarding the status of the release to any subscribed services (block  296 ). 
     Exemplary Implementations 
     A “reference” refers to a piece of data useable to locate a data structure and may be implemented a variety of ways (e.g., a pointer, an index, a handle, a key, an identifier, etc.) 
     Receipt of data by the system may occur differently in different implementations (e.g., it may be pushed to the system (often referred to as a push model), pulled by the system (often referred to as a pull model), etc.) 
     The term “user” is a generic term referring to an entity (e.g., an individual person) using a system and/or service. A multi-tenant architecture provides each tenant with a dedicated share of a software instance and the ability (typically) to input tenant specific data for user management, tenant-specific functionality, configuration, customizations, non-functional properties, associated applications, etc. Multi-tenancy contrasts with multi-instance architectures, where separate software instances operate on behalf of different tenants. A tenant includes a group of users who share a common access with specific privileges to a software instance providing a service. A tenant may be an organization (e.g., a company, department within a company, etc.). A tenant may have one or more roles relative to a system and/or service. For example, in the context of a customer relationship management (CRM) system or service, a tenant may be a vendor using the CRM system or service to manage information the tenant has regarding one or more customers of the vendor. As another example, in the context of Data as a Service (DAAS), one set of tenants may be vendors providing data and another set of tenants may be customers of different ones or all the vendors&#39; data. As another example, in the context of Platform as a Service (PAAS), one set of tenants may be third party application developers providing applications/services and another set of tenants may be customers of different ones or all the third-party application developers. A user may have one or more roles relative to a system and/or service. To provide some examples, a user may be a representative (sometimes referred to as an “end user”) of a tenant (e.g., a vendor or customer), a representative (e.g., an administrator) of the company providing the system and/or service, and/or a representative (e.g., a programmer) of a third-party application developer that is creating and maintaining an application(s) on a Platform as a Service (PAAS). 
     The term “user” is a generic term referring to an entity (e.g., an individual person) using a system and/or service. A multi-tenant architecture provides each tenant with a dedicated share of a software instance and the ability (typically) to input tenant specific data for user management, tenant-specific functionality, configuration, customizations, non-functional properties, associated applications, etc. Multi-tenancy contrasts with multi-instance architectures, where separate software instances operate on behalf of different tenants. A tenant includes a group of users who share a common access with specific privileges to a software instance providing a service. A tenant may be an organization (e.g., a company, department within a company, etc.). A tenant may have one or more roles relative to a system and/or service. For example, in the context of a customer relationship management (CRM) system or service, a tenant may be a vendor using the CRM system or service to manage information the tenant has regarding one or more customers of the vendor. As another example, in the context of Data as a Service (DAAS), one set of tenants may be vendors providing data and another set of tenants may be customers of different ones or all the vendors&#39; data. As another example, in the context of Platform as a Service (PAAS), one set of tenants may be third party application developers providing applications/services and another set of tenants may be customers of different ones or all the third-party application developers. A user may have one or more roles relative to a system and/or service. To provide some examples, a user may be a representative (sometimes referred to as an “end user”) of a tenant (e.g., a vendor or customer), a representative (e.g., an administrator) of the company providing the system and/or service, and/or a representative (e.g., a programmer) of a third-party application developer that is creating and maintaining an application(s) on a Platform as a Service (PAAS). 
     The term “user” is a generic term referring to an entity (e.g., an individual person) using a system and/or service. A multi-tenant architecture provides each tenant with a dedicated share of a software instance and the ability (typically) to input tenant specific data for user management, tenant-specific functionality, configuration, customizations, non-functional properties, associated applications, etc. Multi-tenancy contrasts with multi-instance architectures, where separate software instances operate on behalf of different tenants. A tenant includes a group of users who share a common access with specific privileges to a software instance providing a service. A tenant may be an organization (e.g., a company, department within a company, etc.). A tenant may have one or more roles relative to a system and/or service. For example, in the context of a customer relationship management (CRM) system or service, a tenant may be a vendor using the CRM system or service to manage information the tenant has regarding one or more customers of the vendor. As another example, in the context of Data as a Service (DAAS), one set of tenants may be vendors providing data and another set of tenants may be customers of different ones or all the vendors&#39; data. As another example, in the context of Platform as a Service (PAAS), one set of tenants may be third party application developers providing applications/services and another set of tenants may be customers of different ones or all the third-party application developers. A user may have one or more roles relative to a system and/or service. To provide some examples, a user may be a representative (sometimes referred to as an “end user”) of a tenant (e.g., a vendor or customer), a representative (e.g., an administrator) of the company providing the system and/or service, and/or a representative (e.g., a programmer) of a third-party application developer that is creating and maintaining an application(s) on a Platform as a Service (PAAS). 
     Electronic Device and Machine-Readable Media 
     One or more parts of the above implementations may include software and/or a combination of software and hardware. An electronic device (also referred to as a computing device, computer, etc.) includes hardware and software, such as a set of one or more processors coupled to one or more machine-readable storage media (e.g., magnetic disks, optical disks, read only memory (ROM), Flash memory, phase change memory, solid state drives (SSDs)) to store code (which is composed of software instructions and which is sometimes referred to as computer program code or a computer program) for execution on the set of processors and/or to store data. For instance, an electronic device may include non-volatile memory (with slower read/write times, e.g., magnetic disks, optical disks, read only memory (ROM), Flash memory, phase change memory, SSDs) and volatile memory (e.g., dynamic random access memory (DRAM), static random access memory (SRAM)), where the non-volatile memory persists code/data even when the electronic device is turned off or when power is otherwise removed, and the electronic device copies that part of the code that is to be executed by the set of processors of that electronic device from the non-volatile memory into the volatile memory of that electronic device during operation because volatile memory typically has faster read/write times. As another example, an electronic device may include a non-volatile memory (e.g., phase change memory) that persists code/data when the electronic device is turned off, and that has sufficiently fast read/write times such that, rather than copying the part of the code/data to be executed into volatile memory, the code/data may be provided directly to the set of processors (e.g., loaded into a cache of the set of processors); in other words, this non-volatile memory operates as both long term storage and main memory, and thus the electronic device may have no or only a small amount of volatile memory for main memory. In addition to storing code and/or data on machine-readable storage media, typical electronic devices can transmit code and/or data over one or more machine-readable transmission media (also called a carrier) (e.g., electrical, optical, radio, acoustical or other form of propagated signals—such as carrier waves, infrared signals). For instance, typical electronic devices also include a set of one or more physical network interface(s) to establish network connections (to transmit and/or receive code and/or data using propagating signals) with other electronic devices. Thus, an electronic device may store and transmit (internally and/or with other electronic devices over a network) code and/or data with one or more machine-readable media (also referred to as computer-readable media). 
     Electronic devices are used for a variety of purposes. For example, an electronic device (sometimes referred to as a server electronic device) may execute code that cause it to operate as one or more servers used to provide a service to another electronic device(s) (sometimes referred to as a client electronic device, a client computing device, or a client device) that executes client software (sometimes referred to as client code or an end user client) to communicate with the service. The server and client electronic devices may be operated by users respectively in the roles of administrator (also known as an administrative user) and end user. 
       FIG. 3A  is a block diagram illustrating an electronic device  300  according to some example implementations.  FIG. 3A  includes hardware  320  comprising a set of one or more processor(s)  322 , a set of one or more network interfaces  324  (wireless and/or wired), and non-transitory machine-readable storage media  326  having stored therein software  328  (which includes instructions executable by the set of one or more processor(s)  322 ). Each of the previously described end user clients and the above described cloud service may be implemented in one or more electronic devices  300 . In one implementation: 1) each of the end user clients is implemented in a separate one of the electronic devices  300  (e.g., in user electronic devices operated by users where the software  328  represents the software to implement end user clients to interface with the above described cloud service (e.g., a web browser, a native client, a portal, a command-line interface, and/or an application program interface (API) based upon protocols such as Simple Object Access Protocol (SOAP), Representational State Transfer (REST), etc.)); 2) the above describe cloud service is implemented in a separate set of one or more of the electronic devices  300  (e.g., a set of one or more server electronic devices where the software  328  represents the software to implement the above described cloud service); and 3) in operation, the electronic devices implementing the end user clients and the above described cloud service would be communicatively coupled (e.g., by a network) and would establish between them (or through one or more other layers) connections for submitting requests to the above described cloud service and returning responses to the end user clients. Other configurations of electronic devices may be used in other implementations (e.g., an implementation in which the end user client and the service are implemented on a single electronic device  300 ). 
     In electronic devices that use compute virtualization, the set of one or more processor(s)  322  typically execute software to instantiate a virtualization layer  308  and software container(s)  304 A-R (e.g., with operating system-level virtualization, the virtualization layer  308  represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple software containers  304 A-R (representing separate user space instances and also called virtualization engines, virtual private servers, or jails) that may each be used to execute a set of one or more applications; with full virtualization, the virtualization layer  308  represents a hypervisor (sometimes referred to as a virtual machine monitor (VMM)) or a hypervisor executing on top of a host operating system, and the software containers  304 A-R each represent a tightly isolated form of a software container called a virtual machine that is run by the hypervisor and may include a guest operating system; with para-virtualization, an operating system or application running with a virtual machine may be aware of the presence of virtualization for optimization purposes). Again, in electronic devices where compute virtualization is used, during operation an instance of the software  328  (illustrated as instance  306 A) is executed within the software container  304 A on the virtualization layer  308 . In electronic devices where compute virtualization is not used, the instance  306 A on top of a host operating system is executed on the “bare metal” electronic device  300 . The instantiation of the instance  306 A, as well as the virtualization layer  308  and software containers  304 A-R if implemented, are collectively referred to as software instance(s)  302 . 
     Alternative implementations of an electronic device may have numerous variations from that described above. For example, customized hardware and/or accelerators might also be used in an electronic device. 
     Exemplary Environment 
       FIG. 3B  is a block diagram of an environment where the above discussed release orchestration technique may be used, according to some implementations. A system  340  includes hardware (a set of one or more electronic devices) and software to provide service(s)  342 . The system  340  is coupled to user electronic devices  380 A-S over a network  382 . The service(s)  342  may be on-demand services that are made available to one or more of the users  384 A-S working for one or more other organizations (sometimes referred to as outside users) so that those organizations do not need to necessarily be concerned with building and/or maintaining a system, but instead makes use of the service(s)  342  when needed (e.g., on the demand of the users  384 A-S). The service(s)  342  may communicate with each other and/or with one or more of the user electronic devices  380 A-S via one or more Application Programming Interface(s) (APIs) (e.g., a Representational State Transfer (REST) API). The user electronic devices  380 A-S are operated by users  384 A-S. 
     The application(s) providing one or more of the service(s)  342  are updated from using a current version to an updated version using the above discussed release orchestration technique. Thus, the system  340  includes at least one instance of the COS  102  of  FIG. 1A . 
     The system  340  may be implemented in a single data center or span multiple data centers. In some implementations, at least one instance of the COS  102  is implemented in each of these one or more data center. In the case of multiple instances of the COS  102  different implementations may handle the distribution of the configuration information  122  to the appropriate instance of the COS  102  (e.g., broadcast the configuration information  122  to each instance of the COS  102 , and the instances of the COS  102  determine which is the instance to process the configuration information  122  based upon an identifier in the configuration information  122 ; send the delivery the manifest only to the instance of the COS  102  that is to operate on that the configuration information  122 , etc.). The service discovery service  138  is typically provided by the data center. 
     The service(s)  342 , including the one or more services provided by application(s) that are updated using the above discussed release orchestration technique, include a customer relationship management (CRM) service (e.g., Sales Cloud by salesforce.com, Inc.), a contracts/proposals/quotes service (e.g., Salesforce CPQ by salesforce.com, Inc.), a customer support service (e.g., Service Cloud and Field Service Lightning by salesforce.com, Inc.), a marketing service (e.g., Marketing Cloud, Salesforce DMP, and Pardot by salesforce.com, Inc.), a commerce service (e.g., Commerce Cloud Digital, Commerce Cloud Order Management, and Commerce Cloud Store by salesforce.com, Inc.), communication with external business data sources (e.g., Salesforce Connect by salesforce.com, Inc.), a productivity service (e.g., Quip by salesforce.com, Inc.), database as a service (e.g., Database.com™ by salesforce.com, Inc.), Data as a Service (DAAS) (e.g., Data.com by salesforce.com, Inc.), Platform as a Service (PAAS) (e.g., execution runtime and application (app) development tools; such as, Heroku™ Enterprise, Thunder, and Force.com® and Lightning by salesforce.com, Inc.), an analytics service (e.g., Einstein Analytics, Sales Analytics, and/or Service Analytics by salesforce.com, Inc.), a community service (e.g., Community Cloud and Chatter by salesforce.com, Inc.), an Internet of Things (IoT) service (e.g., Salesforce IoT and IoT Cloud by salesforce.com, Inc.), industry specific services (e.g., Financial Services Cloud and Health Cloud by salesforce.com, Inc.), an Artificial Intelligence service (e.g., Einstein by Salesforce.com, Inc.), and/or Infrastructure as a Service (IAAS) (e.g., virtual machines, servers, and/or storage). For example, system  340  may include an application platform  344  that enables PAAS for creating, managing, and executing one or more applications developed by the provider of the application platform  344 , users accessing the system  340  via one or more of user electronic devices  380 A-S, or third-party application developers accessing the system  340  via one or more of user electronic devices  380 A-S. 
     In some implementations, the system  340  is a multi-tenant cloud computing architecture and one or more of the service(s)  342  may utilize one or more multi-tenant databases  346 , as well as system data storage  350  for system data  352  accessible to system  340 . In certain implementations, the system  340  includes a set of one or more servers that are running on server electronic devices and that are configured to handle requests for any authorized user associated with any tenant (there is no server affinity for a user and/or tenant to a specific server). The user electronic device  380 A-S communicate with the server(s) of system  340  to request and update tenant-level data and system-level data hosted by system  340 , and in response the system  340  (e.g., one or more servers in system  340 ) automatically may generate one or more Structured Query Language (SQL) statements (e.g., one or more SQL queries) that are designed to access the desired information from the one or more multi-tenant database  346  and/or system data storage  350 . 
     In some implementations, the service(s)  342  are implemented using virtual applications dynamically created at run time responsive to queries from the user electronic devices  380 A-S and in accordance with metadata, including: 1) metadata that describes constructs (e.g., forms, reports, workflows, user access privileges, business logic) that are common to multiple tenants; and/or 2) metadata that is tenant specific and describes tenant specific constructs (e.g., tables, reports, dashboards, interfaces, etc.) and is stored in a multi-tenant database. To that end, the program code  360  may be a runtime engine that materializes application data from the metadata; that is, there is a clear separation of the compiled runtime engine (also known as the system kernel), tenant data, and the metadata, which makes it possible to independently update the system kernel and tenant-specific applications and schemas, with virtually no risk of one affecting the others. Further, in one implementation, the application platform  344  includes an application setup mechanism that supports application developers&#39; creation and management of applications, which may be saved as metadata by save routines. Invocations to such applications, including the above described cloud service, may be coded using Procedural Language/Structured Object Query Language (PL/SOQL) that provides a programming language style interface. A detailed description of some PL/SOQL language implementations is discussed in U.S. Pat. No. 7,730,478 entitled, METHOD AND SYSTEM FOR ALLOWING ACCESS TO DEVELOPED APPLICATIONS VIA A MULTI-TENANT ON-DEMAND DATABASE SERVICE, by Craig Weissman, filed Sep. 21, 2007. Invocations to applications may be detected by one or more system processes, which manages retrieving application metadata for the tenant making the invocation and executing the metadata as an application in a software container (e.g., a virtual machine). 
     Network  382  may be any one or any combination of a LAN (local area network), WAN (wide area network), telephone network, wireless network, point-to-point network, star network, token ring network, hub network, or other appropriate configuration. The network may comply with one or more network protocols, including an Institute of Electrical and Electronics Engineers (IEEE) protocol, a 3rd Generation Partnership Project (3GPP) protocol, a 4th generation wireless protocol (4G) (e.g., the Long Term Evolution (LTE) standard, LTE Advanced, LTE Advanced Pro), a fifth generation wireless protocol (5G), or similar wired and/or wireless protocols, and may include one or more intermediary devices for routing data between the system  340  and the user electronic devices  380 A-S. 
     Each user electronic device  380 A-S (such as a desktop personal computer, workstation, laptop, Personal Digital Assistant (PDA), smart phone, augmented reality (AR) devices, virtual reality (VR) devices, etc.) typically includes one or more user interface devices, such as a keyboard, a mouse, a trackball, a touch pad, a touch screen, a pen or the like, video or touch free user interfaces, for interacting with a graphical user interface (GUI) provided on a display (e.g., a monitor screen, a liquid crystal display (LCD), a head-up display, a head-mounted display, etc.) in conjunction with pages, forms, applications and other information provided by system  340 . For example, the user interface device can be used to access data and applications hosted by system  340 , and to perform searches on stored data, and otherwise allow a user  384  to interact with various GUI pages that may be presented to a user  384 . User electronic devices  380 A-S might communicate with system  340  using TCP/IP (Transfer Control Protocol and Internet Protocol) and, at a higher network level, use other networking protocols to communicate, such as Hypertext Transfer Protocol (HTTP), FTP, Andrew File System (AFS), Wireless Application Protocol (WAP), File Transfer Protocol (FTP), Network File System (NFS), an application program interface (API) based upon protocols such as Simple Object Access Protocol (SOAP), Representational State Transfer (REST), etc. In an example where HTTP is used, one or more user electronic devices  380 A-S might include an HTTP client, commonly referred to as a “browser,” for sending and receiving HTTP messages to and from server(s) of system  340 , thus allowing users  384  of the user electronic device  380 A-S to access, process and view information, pages and applications available to it from system  340  over network  382 . 
     CONCLUSION 
     In the above description, numerous specific details such as resource partitioning/sharing/duplication implementations, types and interrelationships of system components, and logic partitioning/integration choices are set forth in order to provide a more thorough understanding. It will be appreciated, however, by one skilled in the art, that the invention may be practiced without such specific details. In other instances, control structures, logic implementations, opcodes, means to specify operands, and full software instruction sequences have not been shown in detail since those of ordinary skill in the art, with the included descriptions, will be able to implement what is described without undue experimentation. 
     References in the specification to “one implementation,” “an implementation,” “an example implementation,” etc., indicate that the implementation described may include a particular feature, structure, or characteristic, but every implementation may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same implementation. Further, when a particular feature, structure, or characteristic is described in connection with an implementation, it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other implementations whether or not explicitly described. 
     For example, the figure(s) illustrating flow diagrams are sometimes described with reference to the figure(s) illustrating block diagrams, and vice versa. Whether or not explicitly described, the alternative implementations discussed with reference to the figure(s) illustrating block diagrams also apply to the implementations discussed with reference to the figure(s) illustrating flow diagrams, and vice versa. At the same time, implementations, other than those discussed with reference to the block diagrams, for performing the flow diagrams are within the scope of this description, and vice versa. 
     Bracketed text and blocks with dashed borders (e.g., large dashes, small dashes, dot-dash, and dots) may be used herein to illustrate optional operations and/or structures that add additional features to some implementations. However, such notation should not be taken to mean that these are the only options or optional operations, and/or that blocks with solid borders are not optional in certain implementations. 
     In the detailed description and claims, the term “coupled,” along with its derivatives, may be used. “Coupled” is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, co-operate or interact with each other. 
     While the flow diagrams in the figures show a particular order of operations performed by certain implementations, it should be understood that such order is exemplary (e.g., alternative implementations may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). 
     While the above description includes several exemplary implementations, those skilled in the art will recognize that the invention is not limited to the implementations described and can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus illustrative instead of limiting.