Mongrel returning empty responses

I’ve recently started having a very strange problem on my brightbox. I’m running the standard setup of Apache + Mongrel and it was working well.

In the last few days I keep getting problems where suddenly every request to the web site gets an empty response. I note that both Apache and both Mongrels continue to run throughout, memory usage is normal but they stop serving.

Sadly, because it’s not dying completely the standard monit setup doesn’t kick it back into life. Anyway, I’d rather discover the root cause of the issue rather than cludging it with a restart script.

Issuing a ‘sudo monit restart all -g blah’ makes everything work again, before it dies a few (random) hours later.

Any ideas?