Oops sorry forgot to mention ...
I am using JBoss 3.0.1RC1.
I am determining the session reuse by showing the session.getId() value. I have made the assumption that a different Id = different session.
Well no one else has answered this ... so I will answer it myself incase other people are struggling with it now or in the future. Put in the web.xml file right after the tag.
Yes, you must mark the webapp distributable. Once you do this, you will get much longer sessionId.
You should also set a snapshot interval so the sessions get distributed back to the returning member. You set this in the jbossweb.sar/META-INF/jboss-service.xml file.
Make sure JBoss is booted and ready *Before* your IP load balancer starts redirecting requests back to the returning member.