How to not lose requests when using Mongrel with Pen

I use lighttpd + pen + Mongrel to serve most of my Rails apps, and so far, I’ve been serving a blank screen to some people after having deployed a new release, and I wasn’t sure why. For some reason I thought the problem was with Mongrel, until I realized that it was probably with pen.

My theory is that when pen tries to serve a request, it notices that all of the backends are suddenly dead, so it serves a blank page. But it also ban the backend process for 30 seconds, so even though it only takes a few for the backends to come back up, they’re now all banned for 30 seconds.

The trick is to add the following two command line parameters: -b 5 -t 10.

What that does is tell pen to only ban a backend for 5 seconds, and to not time out requests for 10 seconds, leaving the Mongrels plenty of time to come back up.