Converged Load Balancing Algorithms

The load balancer automatically uses one of the following algorithms:

• Round-robin algorithm — The load balancer selects the instance for servicing new message in a round robin fashion.

• Consistent hash — The load balancer selects the instance for servicing new message based on hash-key extracted from request. The hash key is extracted by using the rule specified in the DCR file, if provided. If a DCR file is not provided, hash key is extracted using default headers.

  A DCR file, data-centric-rules.xml, provides rules for applying consistent hashing on both HTTP/HTTPS and SIP/SIPS messages from converged or pure SIP applications. If this file is specified, the instructions in this file override the mechanism to extract hash key using default headers. If a DCR file is not provided, SIP and HTTP messages that are part of the same session may be serviced by different instances. Ensure that you provide a DCR file when you are deploying a converged application. The default header used may not provide a correct load distribution for SIP messages either. Therefore, even for pure sip applications, it is recommended that you provide a DCR file. For more information about this file, see Editing Configuration Settings and The Data Centric Rules File.

  In addition to this XML, it is possible to configure DCR by using a plug-in in the form of a Java class.

Converged Load Balancing Algorithm for Web Applications

HTTP and HTTPS messages belonging to pure web applications, the converged load balancer uses a sticky round robin algorithm, by default. When a new request is sent to the load balancer, it is forwarded to an application server instance based on a simple round robin scheme. If the request is for a session-based application, it may result in creation of a session. In such a case, response will have sticky information, which is sent back on subsequent messages. Subsequent messages from the same client for the same session-based application are considered assigned or sticky messages and are routed by the load balancer to the same instance if that instance is found to be healthy. Hence, the name sticky round robin. Requests to a non-session-based application and the first request for a session-based application are new requests.

Converged Load Balancing Algorithm for SIP Applications

For SIP and SIPS messages belonging to pure SIP applications, the converged load balancer uses a consistent hash algorithm, by default. If any of the rules in the DCR file match the SIP/SIPS request, a hash key is extracted using that rule. If none of the instructions or rules in the DCR file match the SIP or SIPS request, a hash key is generated using the from-tag,call-id parameters of the request.

Converged Load Balancing Algorithm for Converged Applications

Converged load balancer applies appropriate algorithms for HTTP/HTTPS and SIP/SIPS messages from converged applications, as follows:

• If no DCR file is specified, applies the sticky round robin algorithm for HTTP/HTTPS messages and the consistent hash algorithm for SIP/SIPS messages.

• If a DCR file is specified, applies the consistent hash algorithm for both HTTP/HTTPS messages and SIP/SIPS messages.

  For HTTP and HTTPS messages belonging to converged applications, if any of the rules in the DCR file match the HTTP/HTTPS request, a hash key is extracted using that rule. If none of the instructions or rules in the DCR file match the HTTP/HTTPS request, a hash key is extracted using remote host and port of the HTTP request.

  For SIP and SIPS messages, if any of the rules in the DCR file match the SIP/SIPS request, a hash key is extracted using that rule. If none of the instructions or rules in the DCR file match the SIP or SIPS request, a hash key is generated using the from-tag,call-id parameters of the request.