8.5 Request Forwarding

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We have already seen that there are some distinct benefits to load balancing since the workload can be spread across multiple servers to improve performance and scalability. But what happens if we must ensure that some requests are only dealt with by, for example, the cluster controller? There is little point in sending a request to have a configuration changed just to see it disappear into a cluster member and not be seen by the controller.

Likewise, if you have a client that has already established session state with a member server, there needs to be a mechanism to force the request to go to one server and one server alone.

This forced direction of requests is called request forwarding. The request forwarder manages session state by using cookies to tie a client to a particular cluster server member. Each time a subsequent request is submitted, the cookie is examined and the appropriate server receives the request.

As we have seen previously, all cluster members receive the workload, but only one server is told by the controller to action the work, while the others will discard it. Request forwarding will add another layer of work to this scenario since the requests will need to be processed, after they have been load balanced; therefore, the site will incur a performance penalty. To reduce the performance penalty, request forwarding can be turned off for specific file types.

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