Clustering and Load Balancing of vaadin application (Urgent)

Dear All,
I am working on clustering and load balancing of vaadin application from last month.
Session Replication is not happening correctly.
Existing Environment Details :

  1. Apache Server is hosted on machine1 for load balancing
    I have configured everything which is required for failover and load balacing and works fine also.
    like worker.properties (mod_jk) , httpd.conf etc.
  2. app1 with tomcat is hosted on machine2
  3. same app1 with tomcat is also hosted on machine3 for load balancing and fail over
    I have configured everything what is required for clustering like implementation of serializable interface , updating of server.xml (port , SimpleTcp Cluster Configurations , add tag in web.xml for both application etc).
    I have simple vaadin application which is displayed combobox and clicking on combox item , one test message will displayed on other page.
    Problem :
    When I shut down machine 2 , then ideally session should be replicated to machine 3 so after refresh the application session should not be expired and page should be displayed i.e. same test message what previously was displayed.
    But every time I am getting vaadin default message in red color “Session Expired” when i shutdown one node.
    On tomcat log , below message is printed.
    “Response has been commited, session expired” - I dont know from where vaadin api commit the reponse when tomcat instance is down.
    Simple jsp based application is working fine , i m getting session expired on vaadin based app only.
    As per some comments received from vaadin group , i had also implemented tomcat valve still it is not working .
    Please help.
    Looking forward to your prompt response.

Please find attached Screen shot for your information.

Regards,
Ashish Patel
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