sessions in multiple tomcats

How do I make multiple tomcats on different servers sharing sessions? I have a balancer sitting in front 开发者_StackOverflow社区of 2 tomcat on two different servers, so when user starts a session, it's only associated with one of the tomcats. He might or might not get the session in the next request.

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i think you can tell it to do sticky sessions, so the LB keeps requests from a client on one app server...

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Difference between session affinity and sticky session?