Clustering Apache Tomcat6

Question

I've got a Java Enterprise Web Application which uses Tomcat6+Struts+Hibernate+MySql. at the time being it's publicly up and running on a single server. In order to performance issues we should move the application to a clustered environment. Anyhow I wanna use Tomcat6 clustering as below:

• A Load Balancing machine including a web server (Apache+mod_proxy) as front-end
• Some application server machines, each one running a tomcat6 instance
• A session management back-end
• And finally a db server

something like this

The load balancer machine receives all the requests and depending on the balancing algorithm redirects them to the respective tomacat6 machine. After doing the business part, the response is returned to the webserver and at the end to the user. In this scenario the front-end machine processes all the requests and responses so it'd be a bottleneck point in the application.

In Apache Tomcat clustering, is there a way to load balancing mechanism and web servers? I mean putting a load balancer in the front end and leave the request/response processing part to multiple web servers.

Answer 1

Tomcat has no support for clustering built in. What happens is that the load balancer distributes requests, so the various Tomcat instances don't need to know what is happening.

What you have to do is to make sure your application can handle it. For example, you must be aware that caches can be stale.

Say instance 1 has object X in it's cache and X is modified by a request processed on instance 2. The cache in instance 2 will be correct, the cache from instance 1 will be stale now.

The solution is to use a cache which supports clustering or disable caching for instances which can be modified. But that doesn't matter to Tomcat.