6.2.1 Distributing workloads

The ability to route a request to any server in a group of clustered application servers allows the servers to share work and improve throughput of client requests. Requests can be evenly distributed to servers to prevent workload imbalances in which one or more servers has idle or low activity while others are overburdened. This load balancing activity is a benefit of workload management.

Thus, the proposed configuration should ensure that each machine or server in the configuration processes a fair share of the overall client load that is being processed by the system as a whole. In other words, it is not efficient to have one machine overloaded while another machine is mostly idle. If all machines have roughly the same capacity (for example, CPU power), each should process a roughly equal share of the load. Otherwise, there likely needs to be a provision for workload to be distributed in proportion to the processing power available on each machine.

Using weighted definitions of cluster members allows nodes to have different hardware resources and still participate in a cluster. The weight specifies that the application server with a higher weight will be more likely to serve the request faster, and workload management will consequently send more requests to that node.

With several cluster members available to handle requests, it is more likely that failures will not negatively affect throughput and reliability. With cluster members distributed to various nodes, an entire machine can fail without any application downtime. Requests can be routed to other nodes if one node fails. Clustering also allows for maintenance of nodes without stopping application functionality.

This section only gives you an introduction into WebSphere WLM. The available WLM policies and how requests are distributed among available servers are described in great detail in Chapter 6 and Chapter 7 of WebSphere Application Server V6 Scalability and Performance Handbook, SG24-6392.

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