Capturing 5xx Errors with a Debug Server

This is an interesting idea - a kind of "goat server", one you feed the stuff the others have already turned down. This could be the one you outfit with the really heavy NewRelic instrumentation and let get bogged down a bit, because there are no users hitting this server.

It could be an interesting addition to the web farm, along with the "canary servers" - web servers identical to your others, taking live traffic, but with fewer compute resources - to catch performance and garbage collection issues before they impact the large boxen.