Workload management is implemented in IBM WAS ND V6 by using appserver clusters and cluster members. These cluster members can all reside on a single node (system) or can be distributed across multiple nodes (or LPARs).
You might have 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.
Workload management (WLM) is the WebSphere facility to provide load balancing and affinity between appservers in a WebSphere clustered environment. It optimizes the distribution of processing tasks in the WAS environment; incoming work requests are distributed to the appservers that can most effectively process the requests.
Workload management is also a procedure for improving performance, scalability, and reliability of an application. It provides failover when servers are not available. WebSphere uses workload management to send requests to alternate members of the cluster. WebSphere also routes concurrent requests from a user to the appserver that serviced the first request, as EJB calls, and session state will be in memory of this appserver.
WLM is most effective when the deployment topology is comprised of appservers on multiple machines, because such a topology provides both failover and improved scalability. It can also be used to improve scalability in topologies where a system is comprised of multiple servers on a single, high-capacity machine. In either case, it enables the system to make the most effective use of the available computing resources.
Two types of requests can be workload managed in IBM WAS ND V6:
When an HTTP request reaches the HTTP server, a decision must be made. Some requests for static content might be handled by the HTTP server. Requests for dynamic content or some static content will be passed to a Web container running in an appserver. 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. We refer to this as Plug-in WLM. For these WebSphere requests, high availability for the Web container becomes an important piece of the failover solution. See 2.5, Web container clustering and failover for more information.
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. We refer to this as EJS WLM. See 2.6, EJB container clustering and failover for additional information.