Between being posted here and on reddit, I'm sure he's getting much more traffic than his host is accustomed to.

Curiously, the server appears to be Apache rather than Jetty.

It is common to have Apache as your static web server to serve images/css/js files and use modules such as mod_rewrite or mod_jk to route to your dynamic context. It seems like his dynamic content server is down (could be the jetty server he was referring to), hence the 503 error code.