Clustered Web messaging enabled applications

You can install a Web messaging enabled application to a cluster like a standard JavaTM Platform, Enterprise Edition (Java EE) application. You can cluster a Web messaging enabled application to take advantage of workload management and limited high availability capabilities.

Application install

Before you install a Web messaging enabled application, verify that each cluster member has the Web messaging service installed and enabled. If a Web messaging enabled application is installed to a server or cluster member without the Web messaging service installed or enabled, incoming Web messaging requests will fail. As a result, errors are issued to the error log. You must also make sure the Web messaging service is installed and enabled if you are adding a a new cluster member to a cluster in which a Web messaging application is installed. See the troubleshooting section for more error information on installation and enablement errors.

Workload management

Installing a Web messaging application to a cluster allows the application to scale beyond the means of a single application server. You should follow the same considerations when installing a Web messaging enabled application to a cluster compared to a regular application. Session affinity is required for Web messaging applications in a clustered environment, and requests must be able to be routed back to the same server, either through the Web server plugin-in or proxy server. Refer to the Clusters and workload management section for more information.

When deploying a Web messaging application to a clustered environment it is also necessary to consider the service integration bus implications of running in a cluster. At a high level, making a cluster into a bus member of a service integration bus makes it possible to create a set of logically equivalent messaging engines that service workload directed to the cluster as described in the Multiple-server bus with clustering topic.

For cluster bus members hosting Web messaging applications, you can configure a 'scalability' style messaging engine configuration to create one messaging engine for each server in the cluster. The 'scalability' style messaging engine configuration also sets policies on each messaging engine so that each engine has a preference for one of the servers in the cluster.

This arrangement means that when Web messaging requests are routed to one of the servers in the cluster there is always a local messaging engine for that server which is capable of handling the necessary messaging actions without communicating with a different server.

The HTTP session affinity mechanism means that once a stateful relationship has been established between Web messaging client (for example, a Web browser) and a specific server in the cluster, subsequent requests by that application is routed back to the same server that the application initially communicated with.

Details on how to configure messaging engines and messaging engine policies in a cluster are found in the following Information Center topics;

Session affinity and failover

In a clustered environment with sesson affinity, if there is a server failure or session affinity breaks down and a request reaches a different server, the Bayeux advice mechanism is used to re-handshake and re-subscribe to all existing topics. In the interval it takes a Web messaging client to re-handshake and re-subscribe to existing topics, messages are missed. The Web messaging service provides a low quality of service in regards to failover. Refer to the service integration bus configuration section for more information on determining appropriate publishing reliability levels


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