Web Application Server Clustering with Distributed Java Virtual Machine

Abstract

Web application servers, being today’s enterprise application backbone, have warranted a wealth of J2EE-based clustering technologies. Most of them however need complex configurations and excessive programming effort to retrofit applications for cluster-aware execution. This chapter proposes a clustering approach based on distributed Java virtual machine (DJVM). A DJVM is a collection of extended JVMs that enables parallel execution of a multithreaded Java application over a cluster. A DJVM achieves transparent clustering and resource virtualization, extolling the virtue of single-systemimage (SSI). The authors evaluate this approach through porting Apache Tomcat to our JESSICA2 DJVM and identify scalability issues arising from fine-grain object sharing coupled with intensive synchronizations among distributed threads. By leveraging relaxed cache coherence protocols, we are able to conquer the scalability barriers and harness the power of our DJVM’s global object space design to significantly outstrip existing clustering techniques for cache-centric web applications.