Using WebSphere Load Balancer custom advisor

  If the WebSphere machine has stopped or the appserver is down while the HTTP server is still running, you will receive an error message on the browser, as illustrated in Figure 3-17.

Figure 3-17 Message when appserver is down

To help us avoid this problem, WebSphere Load Balancer provides a sample custom advisor for WAS. We used this advisor instead of the default HTTP advisor. The layout of our solution is shown in Figure 3-18.

Figure 3-18 Using WebSphere custom advisor

Now, when the WebSphere custom advisor is running, we can continue to access the appserver2 on machine D without getting the error message even when machine C is stopped. The custom advisor directs the request to the HTTP server on machine D, as shown in Figure 3-19.

Figure 3-19 Requests dispatched to active appserver

You cannot run the HTTP advisor and the WebSphere custom advisor at the same time if you specify the same port number for both advisors.

WebSphere custom advisor must be considered as a monitoring extension associated with each HTTP server on the cluster. The custom advisor prevents requests from being sent to a specific HTTP server when this HTTP server cannot appropriately fulfill them (for example, when the WebSphere server it sends requests to is down).

When we use WebSphere workload management, the requests from multiple HTTP servers are sent to a group of appservers, distributed also among multiple machines. We cannot associate the service layer provided by the application server to an HTTP server anymore, since the plug-in is responsible for distributing the requests.

WebSphere custom advisor can have a more meaningful use when WebSphere workload management is not used or a whole cluster associated to a specific HTTP server is down.

When using WebSphere plug-in workload management, as in our sample topology, monitoring the HTTP servers using the HTTP advisor is probably the best choice.

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