Patent Publication Number: US-9432449-B2

Title: Managing connection failover in a load balancer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of and claims the benefit of priority to U.S. patent application Ser. No. 13/965,759, filed Aug. 13, 2013, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure relates generally to an improved data processing system, and, in particular, to a method and apparatus for processing communications. Still more particularly the present disclosure relates to a method and apparatus for managing connection failover in a load balancer. 
     2. Description of the Related Art 
     The Internet is a system of interconnected public and private computer networks. Computing devices communicate with each other over the Internet using a number of Internet protocols. These Internet protocols identify the computing devices and other resources on the Internet using Internet Protocol (IP) addresses and port numbers. Some Internet protocols, such as Transmission Control Protocol/Internet Protocol (TCP/IP), require the establishment of a connection for the communications. For example, after establishing a connection to a resource for a computing device, the computing device may then send requests for information from the resource, send information to the resource, and send a command terminating the connection with the resource. One valuable feature of Internet protocols is that a failure of an intermediate portion of a network will not prevent communications from getting to their destination, as long as there is an alternate path through the network. 
     In some computing environments, use of a resource is distributed across a group of computing devices by a load balancer. Load balancers manage communications between clients and resources. For example, when a client computer sends a request to establish a connection with a resource, a load balancer may intercept the connection. In this example, the load balancer, which is not an endpoint in the connection, responds to the connection request by selecting a particular computing device in a group of computing devices to handle the connection. In this example, the load balancer stores these connections to device mappings in a table that is used by the load balancer to route subsequent communications between client computers and the group of computing devices. 
     Situations may arise where a load balancer has to take over for another load balancer. For example, a planned outage or an unplanned outage of what was a previously active load balancer of a group of resources may result in the start of a process for an alternate load balancer taking over for the previously active load balancer. As with the previous load balancer, the alternate load balancer also needs a mapping table to route communications. The mapping tables of different load balancers are typically located in different data processing systems. If a resource or load balancer receives a communication for a connection that it does not have knowledge of, the typical behavior is to reply to the communication with a connection reset or to discard that communication. The connection reset tells the sender of the communication that the receiver does not know how to handle the communication and the connection should be aborted. Sending a connection reset exposes the situation to the sender of the communication. Exposing the situation is un-desirable in many computing environments. 
     Therefore, a process is needed for synchronizing the mapping tables of the active and alternate load balancers. One solution is to actively synchronize changes between the mapping tables. However, actively synchronizing mapping table changes while the load balancers are processing communications can result in unsatisfactory results. For example, for short lived connections it would be un-desirable to delay creation of connections made by an active load balancer until the connections have been replicated to an alternate load balancer. Similarly, it is also undesirable to process communications while mapping tables are incomplete or out of date due to delayed synchronization of mapping table changes. 
     Therefore, it would be desirable to have a method, apparatus, and computer program product that takes into account at least some of the issues discussed above. 
     SUMMARY 
     In one illustrative embodiment, a method, apparatus, and computer program product for managing communications for a group of servers is disclosed. An apparatus sends to each server in the group of servers a request for connection information for generating a set of mappings for a load balancer of the group of servers to replace another set of mappings for another load balancer of the group of servers. Responsive to receiving a communication from a client device for the group of servers, the apparatus determines whether a route to a server in the group of servers for the communication received from the client device can be identified from the set of mappings for the load balancer and if not, identifies a sub-group of servers in the group of servers that have not yet responded to the request for connection information. The apparatus then forwards the communication to the sub-group of servers in response to a determination that the route to the server in the group of servers for the communication received from the client device cannot be identified from the set of mappings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a load balancing environment for managing communications for a group of servers in accordance with an illustrative embodiment; 
         FIG. 2  is a flow chart of a process for managing communications for a group of servers in accordance with an illustrative embodiment; 
         FIG. 3  is a flow chart of a process for managing communications for a group of servers while replacing a set of mappings of a load balancer of the group of servers in accordance with an illustrative embodiment; and 
         FIG. 4  is an illustration of a data processing system in accordance with an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method, or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store, a program for use by or in connection with an instruction execution system, apparatus, or device. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on remote computers, or entirely on the remote computers. In the latter scenario, the remote computers may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). Further in this latter scenario, the remote computers may include load balancers and servers in a load balancing environment. For example, the load balancers may be network appliances and other types of data processing systems that distribute connections among a group of servers of the load balancing environment. 
     Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     The different illustrative embodiments provide a method, apparatus, and computer program product for managing communications for a group of servers. For example, the different illustrative embodiments may use a process for managing communications for a group of servers over a number of load balancers. For example, a connection failover system may send to each server in the group of servers a request for connection information for generating a set of mappings for a load balancer of the group of servers to replace another set of mappings for another load balancer of the group of servers. Responsive to receiving a communication from a client device for the group of servers, the connection failover system may determine whether a route to a server in the group of servers for the communication received from the client device can be identified from the set of mappings for the load balancer and if not, identifies a sub-group of servers in the group of servers that have not yet responded to the request for connection information. The connection failover system then forwards the communication to the sub-group of servers in response to a determination that the route to the server in the group of servers for the communication received from the client device cannot be identified from the set of mappings. 
     With reference now to the figures and, in particular, with reference to  FIG. 1 , a block diagram of a load balancing environment for managing communications for a group of servers is depicted in accordance with an illustrative embodiment. In this illustrative example, load balancing environment  100  is depicted in block diagram form. 
     As depicted, client applications, such as client applications  106  and client applications  110 , run on computing devices, such as client device  102  and client device  104 . As also depicted, client applications may include web browsers, such as web browser  108  and web browser  112 , and any other client applications that access group of servers  114  in load balancing environment  100 . Client applications access group of servers  114  to create, update, delete, and browse data  116 . In these illustrative examples, data  116  may be a database, memory, a repository, a data processing system, and any other suitable resource for storing, retrieving, updating, and deleting data. For example, data  116  may include websites, such as website  118 . In this example, web browser  108  of client device  102  and web browser  112  of client device  104  may retrieve website  118  from group of servers  114 . As another example, transactions  120  may include transactions managed by group of servers  114  in response to receiving communications from client applications  106  and client applications  110 . For example, transactions  120  may be associated with user input received by web browsers for website  118 . 
     As used herein, a “resource” is one of a computing device, a service hosted by a computing device, and any other suitable type of resource in load balancing environment  100 . As used herein, “a group of,” when used with reference to items, means one or more items. As used herein, “a subgroup of,” when used with reference to a group of items, means one or more items of the group of items. As used herein, “a set of,” when used with reference to items, means one or more items. As used herein, “a subset of,” when used with reference to a set of items, means one or more items of the set of items. 
     In these illustrative examples, client applications running in client devices communicate with group of servers  114  over network  122 . As depicted, access to servers in group of servers  114  is distributed by load balancers, such as load balancer  126  and load balancer  128 , in load balancing environment  100 . As also depicted, the load balancers in load balancing environment  110  communicate with group of servers  114  over network  124 . Network  122  and network  124  are examples of public and private networks over which Internet Protocols are used. For example, network  122  may be the Internet network and any combination of public and private networks for communicating with load balancing environment  100 . In this example, network  124  may be any suitable public or private network for a group of servers managed by load balancers in load balancing environment  100 . 
     As depicted, load balancer  126  and load balancer  128  manage communications between client devices and servers in group of servers  114 , such as server  130 , server  131 , server  132 , server  133 , and any number of other servers in group of servers  114 . For example, responsive to client device  102  sending a request to establish a connection with a resource managed by load balancing environment  100 , load balancer  126  intercepts the request. In this example, load balancer  126  responds to the connection request by selecting a particular server in group of servers  114  based on rules for distributing requests to servers in group of servers  114 . In this example, load balancer  126  selects server  130  to handle communications for the resource requested. Load balancer  126  stores mappings in mapping table  134 , such as mapping  152  of a connection from connections  146  to the selected server  130 . As depicted, server  130  stores connections established with server  130  in connections  138 , server  131  stores connections established with server  131  in connections  140 , server  132  stores connections established with server  132  in connections  142 , and server  133  stores connections established with server  133  in connections  144 . As also depicted, client device  102  stores connections established with client device  102  in connections  146  and client device  104  stores connections established with client device  104  in connections  148 . In these illustrative examples, load balancer  126  uses mapping table  134  to forward communications between client devices and servers in group of servers  114 , and load balancer  128  uses mapping table  136  to forward communications between client devices and servers in group of servers  114 . 
     As used herein, a “connection” is a connection for a networking protocol such as an Internet protocol. For example, a connection may be for a particular protocol for communicating with a particular resource by using an internet protocol (IP) address and port number for the resource. The load balancer is aware of the distinguishing characteristics of each connection it distributes, but is not an endpoint of the connection. The connection itself extends from a client device to one and only one server. For example, a connection in connections  146  extends from client device  102  through network  122 , through load balancer  126 , through network  124 , to one and only one server in group of servers  114 . In this example, client application  106  sends a request to load balancing environment  100 , and if load balancer  126  selects server  130 , then the same connection appears in connections  138  and in connections  146 . In this example, mapping table  134  stores a description of the connection and that the connection was distributed to server  130 . 
     In these illustrative examples, load balancing environment  100  includes connection failover system  150 . Responsive to a planned or an unplanned outage of load balancer  126 , connection failover system  150  begins a process for managing communications for group of servers  114  while replacing mapping table  134  of load balancer  126 . For example, the process for managing communications for group of servers  114  while replacing mapping table  134  of load balancer  126  may include load balancer  128  taking over for load balancer  126 . In this example, at the beginning of the process mapping table  136  does not have the same mappings as mapping table  134 . In this example, mapping  152  is an example of a mapping between client device  102  and server  130 . Mappings, such as mapping  152 , comprise connection information, such as a client internet protocol address and port number and a server internet protocol address and port number. Still further in this example, connection failover system  150  sends request  158  to each server in group of servers  114  as a request for connection information for generating a mapping table for a load balancer of group of servers  114  to replace mapping table  134 . 
     In these illustrative examples, when one of the servers in group of servers  114  receives request  158 , the server responds by sending a copy of the connections in the server to connection failover system  150 . When connection failover system  150  receives the copies of the connections from the servers, connection failover system  150  uses the copies to generate a new mapping table, such as mapping table  136 . For example, connection failover system  150  may use a copy of the connections received from server  130  to recreate the mappings in mapping table  134 , such as by replacing mapping  152  with mapping  162  in mapping table  136  in load balancer  128 . 
     As depicted, connection failover system  150  may also send command  170  to each server in group of servers  114  as a command to suppress or resume sending connection reset messages when a message is received for an unknown connection. For example, connection failover system  150  may send command  170  to each server in group of servers  114  as a command to suppress sending connection reset messages when messages are received for unknown connections at the same time as request  158  is sent. In this example, subsequent to receiving responses from each server in group of servers  114  for request  158 , connection failover system  150  may send another command to each server in group of servers  114  as a command to resume sending connection reset messages when messages are received for unknown connections. 
     The illustration of load balancing environment  100  in  FIG. 1  is not meant to imply physical or architectural limitations to the manner in which different illustrative embodiments may be implemented. Other components in addition to and/or in place of the ones illustrated may be used. Some components may be unnecessary. Also, the blocks are presented to illustrate some functional components. One or more of these blocks may be combined and/or divided into different blocks when implemented in an illustrative embodiment. 
     For example, in some illustrative examples, additional load balancers in addition to load balancer  126  and load balancer  128  may be present within domain name services management environment  100 . Also, although connection failover system  150  is shown as a separate block in load balancing environment  100 , all or a portion of connection failover system  150  may also be implemented in any or all of the load balancers and servers in load balancing environment  100 . In these illustrative examples, connection failover system  150  may be implemented by any combination of hardware and software products, and may also be implemented in one or more computer systems of a cluster of computer systems. 
     Turning now to  FIG. 2 , an illustrative example of a flowchart of a process for managing communications for a group of servers is depicted in accordance with an illustrative embodiment. The steps in the process may be implemented in software, hardware, or a combination of the two by connection failover system  150  in load balancing environment  100  in  FIG. 1 . 
     The process begins by sending a request for connection information for generating a set of mappings to a group of servers (step  200 ). In this illustrated process, the request is an example of request  158  in  FIG. 1 , the set of mappings is an example of mapping table  136  in  FIG. 1 , and the group of servers is an example of group of servers  114  in  FIG. 1 . 
     The process begins another process for generating the set of mappings from responses to the request from the group of servers (step  201 ). Responsive to receiving a communication from a client device for the group of servers, the process determines whether a server in the group of servers for the communication can be identified from the set of mappings (step  202 ). 
     As depicted, if the server has been identified from the set of mappings, the process forwards the communication to the identified server (step  210 ) with the process terminating thereafter. If the server cannot be identified from the set of mappings, the process next identifies a sub-group of servers in the group of servers that have not yet responded to the request for connection information (step  204 ). As illustrated, if the sub-group of servers contains one or more servers, the process forwards the communication to the sub-group of servers (step  206 ) with the process terminating thereafter. If the sub-group of servers does not contain one or more servers, the process drops the communication (step  208 ) with the process terminating thereafter. In the illustrative examples, a mapping for a communication is identified in a mapping table by identifying a mapping in the mapping table that has the same source and destination, such as client and server, for the communication. 
     The illustrative embodiments recognize and take into account that existing network protocols such as Transmission Control Protocol/Internet Protocol (TCP/IP), establish connections for communications between clients and resources. For example, after a client computing device establishes a TCP/IP connection to a resource, the client computing device may then send requests for information from the resource, send information to the resource, send a command terminating the connection with the resource, and wait for a response. While waiting for a response, the information requested may be sent from the resource to the client. Additionally, a reset notification may be sent to the client from the resource and from any another data processing system functioning between the client and the resource, the reset notification informing the client that the connection should be terminated. 
     Turning next to  FIG. 3 , an illustrative example of a flowchart of a process for managing communications for a group of servers while replacing a set of mappings of a load balancer of the group of servers is depicted in accordance with an illustrative embodiment. The steps in the process may be implemented in software, hardware, or a combination of the two by connection failover system  150  in load balancing environment  100  in  FIG. 1 . 
     The process begins by receiving a request for connection information for generating a set of mappings to a server (step  300 ). In this illustrated process, the request is an example of request  158  in  FIG. 1 , the set of mappings is an example of mapping table  136  of load balancer  128  in  FIG. 1 , and the server is an example of one of group of servers  114  in  FIG. 1 . 
     Responsive to receiving the request, the process blocks the server from sending connection reset notifications (step  302 ). As depicted, the process generates a list of mappings to the server based on connection information from prior connections made between clients and the server (step  304 ). The process sends the list of mappings in response to the request (step  306 ). 
     The process determines if the server should resume sending connection reset notifications based on one of the sending of the generated list of mappings, receiving notification to resume sending connection reset notifications, and a timer expiring (step  306 ), and if so, the process then allows the server to resume sending connection reset notifications (step  308 ) with the process terminating thereafter. 
     Turning now to  FIG. 4 , an illustration of a data processing system is depicted in accordance with an illustrative embodiment. Data processing system  400  is an example of a data processing system that may be used to managing communications for a group of servers in a connection failover system. Data processing system  400  is also an example of a data processing system that may be used to implement client device  102 , client device  104 , data  116 , load balancer  126 , load balancer  128 , server  130 , server  131 , server  132 , and server  133  in  FIG. 1 . More particularly, data processing system  400  may be used to implement connection failover system  150  in  FIG. 1 . In this illustrative example, data processing system  400  includes communications framework  402 , which provides communications between processor unit  404 , memory  406 , persistent storage  408 , communications unit  410 , input/output (I/O) unit  412 , and display  414 . In these examples, communications frame work  402  may be a bus system. 
     Processor unit  404  serves to execute instructions for software that may be loaded into memory  406 . Processor unit  404  may be a number of processors, a multi-processor core, or some other type of processor, depending on the particular implementation. A number, as used herein with reference to an item, means one or more items. Further, processor unit  404  may be implemented using a number of heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, processor unit  404  may be a symmetric multi-processor system containing multiple processors of the same type. 
     Memory  406  and persistent storage  408  are examples of storage devices  416 . A storage device is any piece of hardware that is capable of storing information, such as, for example, without limitation, data, program code in functional form, and/or other suitable information either on a temporary basis and/or a permanent basis. Storage devices  416  may also be referred to as computer readable storage devices in these examples. Memory  406 , in these examples, may be, for example, a random access memory or any other suitable volatile or non-volatile storage device. Persistent storage  408  may take various forms, depending on the particular implementation. 
     For example, persistent storage  408  may contain one or more components or devices. For example, persistent storage  408  may be a hard drive, a flash memory, a rewritable optical disk, a rewritable magnetic tape, or some combination of the above. The media used by persistent storage  408  also may be removable. For example, a removable hard drive may be used for persistent storage  408 . 
     Communications unit  410 , in these examples, provides for communications with other data processing systems or devices. In these examples, communications unit  410  is a network interface card. Communications unit  410  may provide communications through the use of either or both physical and wireless communications links. 
     Input/output unit  412  allows for input and output of data with other devices that may be connected to data processing system  400 . For example, input/output unit  412  may provide a connection for user input through a keyboard, a mouse, and/or some other suitable input device. Further, input/output unit  412  may send output to a printer. Display  414  provides a mechanism to display information to a user. 
     Instructions for the operating system, applications, and/or programs may be located in storage devices  416 , which are in communication with processor unit  404  through communications framework  402 . In these illustrative examples, the instructions are in a functional form on persistent storage  408 . These instructions may be loaded into memory  406  for execution by processor unit  404 . The processes of the different embodiments may be performed by processor unit  404  using computer implemented instructions, which may be located in a memory, such as memory  406 . 
     These instructions are referred to as program code, computer usable program code, or computer readable program code that may be read and executed by a processor in processor unit  404 . The program code in the different embodiments may be embodied on different physical or computer readable storage media, such as memory  406  or persistent storage  408 . 
     Program code  418  is located in a functional form on computer readable media  420  that is selectively removable and may be loaded onto or transferred to data processing system  400  for execution by processor unit  404 . Program code  418  and computer readable media  420  form computer program product  422  in these examples. In one example, computer readable media  420  may be computer readable storage media  424  or computer readable signal media  426 . Computer readable storage media  424  may include, for example, an optical or magnetic disk that is inserted or placed into a drive or other device that is part of persistent storage  408  for transfer onto a storage device, such as a hard drive, that is part of persistent storage  408 . Computer readable storage media  424  also may take the form of a persistent storage, such as a hard drive, a thumb drive, or a flash memory, that is connected to data processing system  400 . In some instances, computer readable storage media  424  may not be removable from data processing system  400 . In these examples, computer readable storage media  424  is a physical or tangible storage device used to store program code  418  rather than a medium that propagates or transmits program code  418 . Computer readable storage media  424  is also referred to as a computer readable tangible storage device or a computer readable physical storage device. In other words, computer readable storage media  424  is a media that can be touched by a person. 
     Alternatively, program code  418  may be transferred to data processing system  400  using computer readable signal media  426 . Computer readable signal media  426  may be, for example, a propagated data signal containing program code  418 . For example, computer readable signal media  426  may be an electromagnetic signal, an optical signal, and/or any other suitable type of signal. These signals may be transmitted over communications links, such as wireless communications links, optical fiber cable, coaxial cable, a wire, and/or any other suitable type of communications link. In other words, the communications link and/or the connection may be physical or wireless in the illustrative examples. 
     In some illustrative embodiments, program code  418  may be downloaded over a network to persistent storage  408  from another device or data processing system through computer readable signal media  426  for use within data processing system  400 . For instance, program code stored in a computer readable storage medium in a server data processing system may be downloaded over a network from the server to data processing system  400 . The data processing system providing program code  418  may be a server computer, a client computer, or some other device capable of storing and transmitting program code  418 . 
     The different components illustrated for data processing system  400  are not meant to provide architectural limitations to the manner in which different embodiments may be implemented. The different illustrative embodiments may be implemented in a data processing system including components in addition to or in place of those illustrated for data processing system  400 . Other components shown in  FIG. 4  can be varied from the illustrative examples shown. The different embodiments may be implemented using any hardware device or system capable of running program code. As one example, the data processing system may include organic components integrated with inorganic components and/or may be comprised entirely of organic components excluding a human being. For example, a storage device may be comprised of an organic semiconductor. 
     In another illustrative example, processor unit  404  may take the form of a hardware unit that has circuits that are manufactured or configured for a particular use. This type of hardware may perform operations without needing program code to be loaded into a memory from a storage device to be configured to perform the operations. 
     For example, when processor unit  404  takes the form of a hardware unit, processor unit  404  may be a circuit system, an application specific integrated circuit (ASIC), a programmable logic device, or some other suitable type of hardware configured to perform a number of operations. With a programmable logic device, the device is configured to perform the number of operations. The device may be reconfigured at a later time or may be permanently configured to perform the number of operations. Examples of programmable logic devices include, for example, a programmable logic array, a programmable array logic, a field programmable logic array, a field programmable gate array, and other suitable hardware devices. With this type of implementation, program code  418  may be omitted because the processes for the different embodiments are implemented in a hardware unit. 
     In still another illustrative example, processor unit  404  may be implemented using a combination of processors found in computers and hardware units. Processor unit  404  may have a number of hardware units and a number of processors that are configured to run program code  418 . With this depicted example, some of the processes may be implemented in the number of hardware units, while other processes may be implemented in the number of processors. 
     In another example, a bus system may be used to implement communications framework  402  and may be comprised of one or more buses, such as a system bus or an input/output bus. Of course, the bus system may be implemented using any suitable type of architecture that provides for a transfer of data between different components or devices attached to the bus system. 
     Additionally, a communications unit may include a number of more devices that transmit data, receive data, or transmit and receive data. A communications unit may be, for example, a modem or a network adapter, two network adapters, or some combination thereof. Further, a memory may be, for example, memory  406 , or a cache, such as found in an interface and memory controller hub that may be present in communications framework  402 . 
     Thus, the illustrative embodiments provide a method, apparatus, and computer program product for managing communications for a group of servers. In one example, a program runs in a computer system and manages communications for a group of servers over a number of load balancers. In this example, the program sends to each server in the group of servers a request for connection information for generating a set of mappings for a load balancer of the group of servers to replace another set of mappings for another load balancer of the group of servers. Responsive to receiving a communication from a client device for the group of servers, the program determines whether a route to a server in the group of servers for the communication received from the client device can be identified from the set of mappings for the load balancer and if not, identifies a sub-group of servers in the group of servers that have not yet responded to the request for connection information. The program forwards the communication to the sub-group of servers in response to a determination that the route to the server in the group of servers for the communication received from the client device cannot be identified from the set of mappings. For example, these steps may be responsive to a need to replace the other set of mappings for the other load balancer of the group of servers. The need to replace the load balancer may be a scheduled outage or an unscheduled outage, such as due to a failure associated with the other load balancer. In this and other examples, the program may suppress connection reset messages that would otherwise be sent to the client device until the set of mappings for the load balancer has been generated from responses to the requests. For example, the program may send commands to the group of servers or the sub-group of servers to suppress sending connection reset notifications until the set of mappings has been generated. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the phrase “at least one of”, when used with a list of items, means that different combinations of one or more of the listed items may be used and only one of each item in the list may be needed. For example, “at least one of item A, item B, and item C” may include, for example, without limitation, item A, or item A and item B. This example also may include item A, item B, and item C, or item B and item C. In other examples, “at least one of” may be, for example, without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; and other suitable combinations. 
     The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be performed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.