For Tomcat clustering, if we are using mod_jk as a front-end load balancer, JBoss is supposed to insert a JvmRouteFilter in front of every web app to check on the fail-over scenario and replace the route name, if necessary. Currently, it is not working in 4.0. Not sure if it is a regression problem or not.

The consequence is:

req 1 goes to server 1
server 1 goes down, req 2 (same session) goes to server 2
server 1 is up, req 3 (same session) comes back to server 1

But the failover should still work.

This is discovered in salesforce:
https://na1.salesforce.com/50030000000wdvX