Clustered session support

 

A clustered environment supports load balancing, where the workload is distributed among the appservers that compose the cluster.

In a cluster environment, the same Web application must exist on each of the servers that can access the session. You can accomplish this setup by installing an application onto a cluster definition. Each of the servers in the group can then access the Web application

In a clustered environment, the session management facility requires an affinity mechanism so that all requests for a particular session are directed to the same appserver instance in the cluster. This requirement conforms to the Servlet 2.3 specification in that multiple requests for a session cannot coexist in multiple appservers. One such solution provided by IBM WAS is session affinity in a cluster; this solution is available as part of the WAS plug-ins for Web servers. It also provides for better performance because the sessions are cached in memory. In clustered environments other than WebSphere Application Server clusters, use an affinity mechanism (for example, IBM WebSphere Edge Server affinity).

If one of the servers in the cluster fails, it is possible for the request to reroute to another server in the cluster. If distributed sessions support is enabled, the new server can access session data from the database or another WAS instance. You can retrieve the session data only if a new server has access to an external location from which it can retrieve the session.

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Related tasks

Task overview: Managing HTTP sessions

 

Related Reference

HTTP sessions: Resources for learning