6.2 WebSphere workload management defined
Workload management is implemented in IBM WebSphere Application Server Network Deployment V6 by using application server 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 thick Java/C++ clients. When using clustered WebSphere Application Servers, 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 application server.
Workload management (WLM) is the WebSphere facility to provide load balancing and affinity between application servers in a WebSphere clustered environment. It optimizes the distribution of processing tasks in the WebSphere Application Server environment. Incoming work requests are distributed to the application servers 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 application server that serviced the first request, as EJB calls, and session state will be in memory of this application server.
WLM is most effective when the deployment topology comprises application servers 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 comprises 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 WebSphere Application Server Network Deployment V6:
- HTTP requests can be distributed across multiple Web containers. 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 application server. Whether the request should be handled or passed to WebSphere is decided by the IBM HTTP 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 6.3, Web container clustering and failover (Web server plugin), for more information.
- EJB requests can be distributed across multiple EJB containers. 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 application servers. If that server fails, the client request is redirected to another available server. We refer to this as EJS WLM.
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