High availability Tomcat: "Connect Tomcat servers to Apache and to each other to keep your site running
If you run only one instance of Tomcat, you lose requests/sessions whenever you upgrade or restart your site. In this article, author Graham King presents simple steps for connecting a pair (or more) of Tomcats to Apache using the JK2/AJP (Apache JServ Protocol) connector and to each other using Tomcat 5's clustering capabilities. Any of the Tomcat servers can be stopped or started without affecting users. With an Apache/Tomcat cluster in place, you can easily adjust your configuration for a range of load-balancing and failover scenarios. (2,000 words; December 20, 2004)"