Pier Fumagalli sends an email I wish I'd see 2 years ago: [TIPS] Basic configurations of Apache 2.0 for Cocoon 2, aka how to avoid the whole mod_jk/mod_jk2/mod_webapp mess and connect Apache and a web server with minimal fuss using mod_proxy and mod_rewrite.

Tomcat's Proxy HOWTO explains how to prevent HttpRequest.getServerPort() and HttpUtils.getRequestURL() breaking.