Setting the MaxInactiveInterval for a web session can cause sessions to be evicted early on failover nodes as the MaxInactiveInterval is a part of the marshalled session which is only unmarshalled on failover. The web.xml session timeout is used for eviction of marshalled sessions.

If the MaxInactiveInterval is set to 90 minutes, but the web.xml session timeout is set to 30 minutes, the session can be evicted early preventing failover for a given session. If the opposite occurs and the MaxInactiveInterval is set to 30 minutes and the web.xml session timeout is set to 90 minutes, the session will not be used during failover if the MaxInactiveInterval has already elapsed. If failover doesn't occur (and in most cases it will not), the marshalled session will remain in memory until the web.xml session timeout has elapsed.

This JIRA is meant to track the early expiration problem. Setting the web.xml session timeout to the largest value that will ever be used for the MaxInactiveInterval will prevent early eviction, but it can cause sessions to accumulate in memory. By using a sensibly small web.xml session timeout coupled with the fix detailed in this JIRA, early eviction will be avoided completely and large amounts of unnecessary accumulation can be avoided (but it won't be avoided completely).