This is an article of mine first published on Wazi
The mod_jk connector serves as the glue between the Apache HTTP server and a Java application server such as Tomcat or JBoss. While most adminstrators concentrate on optimizing Apache or the Java server, setting up mod_jk optimally can also improve your users’ experience.
To be precise, mod_jk connects the Apache web server to the AJP port of a Java server. Apache Jserv Protocol is a binary version of HTTP that is optimized for communication over TCP between the Apache HTTP server and Apache Tomcat or other software.