Vaadin 6 - Session problem


I have an application written with Vaadin 6 and I cannot switch to Vaadin 7.

I’m experiencing a problem with sessions.
In my web.xml configuration file i set session-timeout property to 120, but sometimes I get “Session expired” message from the application before 120 minutes, it seems that the session still lasts about 30 minutes.

My application is deployed on 2 balanced servers and I cannot access to the balancer server.

I have 2 ideas about this:

  1. The balancer server (Apache) has a timeout that destroy also application session. I’m not an expert on this argument so I don’t know if it is possible.
  2. If the tab with application is not focused (another tab opened with any site, not the application) it cannot send anything to the server and the session is destroyed before the maximum (120). But I don’t think this is the case.

Any suggestion on how can I fix this?