Overview

 

WAS V5 provides support for creating an appserver cluster using a server template. This concept is different from the server group in WAS V4; the server template or model is not active in Version 5, and a change to the model will not impact cluster servers after creation. Server templates can contain a Web container, an EJB container, or both. From a server template, a WebSphere administrator can create any number of application server instances, or cluster members. These cluster members can all reside on a single node (systems) or can be distributed across multiple nodes in the WebSphere domain or WebSphere cell. Cluster members can be administered as a single unit by manipulating the server cluster object. Cluster members can share application workload and provide failover support. All servers can be manually divided into primary servers and backup servers. If one of the primary servers fails, work can continue to be handled by other primary servers in the server cluster, as long as primary servers are still available. If all the primary servers are unavailable, the request will fail over to the first backup server. If the first backup server fails, the next backup server will be used.

You may have thin Web clients or/and thick Java/C++ clients. When using clustered WASs, your clients can be redirected either automatically or manually (depending on the nature of the failure) to another healthy server in the case of a failure of a clustered appserver.

When an HTTP request reaches the HTTP server, a decision must be made. Some requests for static content may be handled by the HTTP server. Requests for dynamic content or some static content will be passed to a Web container running in a WAS. Whether the request should be handled or passed to WebSphere is decided by the WebSphere Web server plug-in, which runs in-process with the HTTP server. For these WebSphere requests, high availability for the Web container becomes an important piece of the failover solution.

When an EJB client makes calls from the Web container or client container or from outside, the request is handled by the EJB container in one of the clustered appservers. If that server fails, the client request is redirected to another available server.

If you don't workload manage your WASs and you don't use any other clustering software, your system will not provide any failover support. All of your Web or Java clients will fail if your WAS fails.

If you workload manage your WebSphere cluster servers, your system provides satisfactory failover support for most cases. In addition, when using other clustering software such as HACMP, Sun Cluster Server, VERITAS Cluster Server, MC/ServiceGuard, and Microsoft Cluster Service, you also can provide the automatic failover and recovery of two-phase transactions and hosts.

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IBM is a trademark of the IBM Corporation in the United States, other countries, or both.