Evaluation of a Group Communication Middleware for Clustered J2EE Application Servers

Clusters have become the de facto platform to scale J2EE application servers. Each tier of the server uses group communication to maintain consistency between replicated nodes. JGroups is the most commonly used Java middleware for group communications in J2EE open source implementations. No evaluation has been done yet to evaluate the scalability of this middleware and its impact on application server scalability. We present an evaluation of JGroups performance and scalability in the context of clustered J2EE application servers. We evaluate the JGroups configuration used by popular software such as the Tomcat JSP server or JBoss J2EE server. We benchmark JGroups with different network technologies, protocol stacks and cluster sizes. We show, using the default protocol stack, that group communication performance using UDP/IP depends on the switch capability to handle multicast packets. Fast Ethernet can give better results than Gigabit Ethernet. We experiment with another configuration using TCP/IP and show that current J2EE application server clusters up to 16 nodes (the largest configuration we tested) can scale much better with this configuration. We attribute the superiority of TCP/IP based group communications over UDP/IP multicast to a better flow control management and a better usage of the network switches available in cluster environments. Finally, we discuss architectural improvements for a better modularity and resource usage of JGroups channels.