Chapter 1. Overview

Apache HTTP Server ("Apache") is a well-known web server which can be extended using plug-ins. The Apache Tomcat Connector mod_jk is a plug-in designed to allow request forwarding from Apache HTTP Server to a servlet container. The module also supports load-balancing HTTP calls to a set of servlet containers while maintaining sticky sessions.
HTTP session replication is used to replicate the state associated with web client sessions to other nodes in a cluster. If one node becomes unavailable, another node in the cluster continues to service the failed node's requests. This involves two distinct operations:
  • Session state replication
  • Load-balancing HTTP Requests
Session state replication is handled by JBoss per application, providing the application is configured to make use of this feature (refer to Section 17.1, “Enabling session replication in your application”).
Load balancing must be handled externally to JBoss, via either hardware or software. A cost-effective way of enabling load balancing is to set up a software load balancer using Apache HTTP Server and the Apache Tomcat Connector (mod_jk).