Friday, 23 August 2013

From the Twitter stream - IBM web server plug-in is not load balancing evenly

Problem(Abstract)

IBM web server plug-in appears to not be load balancing correctly. Too much load is going to only one of the members (application servers) in the cluster. Why is this happening?

Symptom

During load testing, you might notice that a lot more work is being handled by only 1 application server in the cluster. However, the other application servers in the same cluster are much less busy by comparison.

Cause

The IBM web server plug-in only load balances non-affinity requests. These are new requests that do not have a session cookie (JSESSIONID) in the request.

On the other hand, if it is an affinity request, that does have a session cookie (JSESSIONID), then the plug-in will honor session affinity by sending the request to the same application server as before. It will use the application server which matches the cloneid in the JSESSIONID cookie.

Want to know more ? Then read the IBM Technote 1449249 here: -

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