mod_jk vs mod_cluster

Question

Can someone please tell me the pro's and con's of mod_jk vs mod_cluster.

We are looking to do very simple load balancing.. We are going to be using sticky sessions and just need something to route new requests to a new server if one server goes down. I feel that mod_jk does this and does a good job so why do I need mod_cluster?

Answer 1

If your JBoss version is 5.x or above, you should use mod_cluster, it will give you a better performance and reliability than mod_jk. Here you've some reasons:

• better load balacing between app servers: the load balancing logic is calculated based on information and metrics provided directly by the applications servers (bear in mind they have first hand information about its load), in contrast with mod_jk with which the logic is calculated by the proxy itself. For that, mod_cluster uses an extra connection between the servers and the proxy (a part from the data one), used to send this load information.
• better integration with the lifecycle of the applications deployed in the servers: the servers keep the proxy informed about the changes of the application in each respective node (for example if you undeploy the application in one of the nodes, the node will inform the proxy (mod_cluster) immediately, avoiding this way the inconvenient 404 errors.
• it doesn't require ajp: you can also use it with http or https.
• better management of the servers lifecycle events: when a server shutdowns or it's restarted, it informs the proxy about its state, so that the proxy can reconfigure itself automatically.

You can use sticky sessions as well with mod cluster, though of course, if one of the nodes fails, mod cluster won't help to keep the user sessions (as it would happen as well with other balancers, unless you've the JBoss nodes in cluster). But due to the reasons given above (keeping track of the server lifecycle events, and better load balancing mainly), in case one of the servers goes down, mod cluster will manage it better and more transparently to the user (the proxy will be informed immediately, and so it will never send requests to that node, until it's informed that it's restarted).

Remember that you can use mod_cluster with JBoss AS/EAP 5.x or JBoss Web 2.1.1 or above (in the case of Tomcat I think it's version 6 or above).

To sum up, though your use case of load balancing is simple, mod_cluster offers a better performance and scalability.

You can look for more information in the JBoss site for mod_cluster, and in its documentation page.