3 medium sized dell frontend servers running jboss4 and one beefy backend mysql server. we ran our own bare metal because this was before 'cloud' services would allow porn sites to operate.
the ejb3 caching was so efficient that we really only needed one server, we just had the other two as backup so that we could do CI driven rolling deploys integrated with the load balancer. we used jgroups mcast to expire entities in the cache. jvms were carefully monitored and all the settings were heavily tuned for our environment.
the hardest thing about all of it was simply packaging it all up into a war file correctly. it is all knowledge that i've long since forgotten how to do.
I was thinking of the EJB 1 & 2 era xml wiring of all the things.