What kind of application, specifically? The details will be different for EARs, WARs or standalone JARs. For example, for WARs it would mean having multiple
servlet containers, each with their associated "webapps" directory (as it's called in
Tomcat) - so you can deploy the WAR in each Tomcat. Of course, you need to make sure you can access those various servlet containers - maybe they're set up on different ports if running on the same machine, or maybe they run on different machines (so they'd have different IP addresses).