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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