Load Balancing Tomcat 7 for Application Deployment

Question

I am serving a java app through apache mod_jk and tomcat 7. I want to be able to deploy a new instance of the application ( on a separate tomcat instance) that will accept all new sessions. However all existing sessions will continue to be served by the old tomcat. Then after all users have logged off or after a certain time the old server will be shut down and all traffic will be handled by the new tomcat ( I don't expect the load balancer to do this ). This will allow me to deploy without disrupting any connected users.

I have read about mod_jk lad balancing which provides the sticky sessions that I need but I have not found how to force all new sessions to be served from the new application. It looks simple enough to set up a round robbin, but that is not what i want.

So the formal question is:

Are there any load balancers for tomcat7/apache that will allow me to customize balancing rules to respect sticky sessions but preferentially serve from one node?

Any thoughts on how to best achieve this?

Answer 1

Each node manages it's own session data. To remove a node with minimal disruptuion to connected users you need to share session data across all nodes. Tomcat provides session replication for this. Even with replication, it is possilbe that a node may crash before it has shared it's data. There are other solutions as dicussed here

Answer 2

Tomcat supports running multiple versions of the one web application with the Parallel Deployment feature. When a new session is created, it will be using the most recent version of the web application. Existing sessions will continue to use the version of the web application that was the most recent at the session creation time.

Here is an article that discusses Parallel Deployment: http://www.objectpartners.com/2012/04/17/tomcat-v7-parallel-deployment/