If you are using mod_jk and not using sticky sessions or for some reasons sticky session don’t work, or you are simply failing over, the session id will need to be modified as it previously contained the worker id of the previous tomcat (as defined by jvmRoute in the Engine element). To solve this, we will use the JvmRouteBinderValve.
The JvmRouteBinderValve rewrites the session id to ensure that the next request will remain sticky (and not fall back to go to random nodes since the worker is no longer available) after a fail over. The valve rewrites the JSESSIONID value in the cookie with the same name. Not having this valve in place, will make it harder to ensure stickiness in case of a failure for the mod_jk module.
Remember, if you are adding your own valves in server.xml then the defaults are no longer valid, make sure that you add in all the appropriate valves as defined by the default.
Hint:
With attribute sessionIdAttribute you can change the request attribute name that included the old session id. Default attribute name is org.apache.catalina.ha.session.JvmRouteOrignalSessionID.
Trick:
You can enable this mod_jk turnover mode via JMX before you drop a node to all backup nodes! Set enable true on all JvmRouteBinderValve backups, disable worker at mod_jk and then drop node and restart it! Then enable mod_jk Worker and disable JvmRouteBinderValves again. This use case means that only requested session are migrated.
