We’ve been running Unicorn for more than a month. Time to talk about it.

Unicorn is an HTTP server for Ruby, similar to Mongrel or Thin. It uses Mongrel’s Ragel HTTP parser but has a dramatically different architecture and philosophy.

In the classic setup you have nginx sending requests to a pool of mongrels using a smart balancer or a simple round robin.

Eventually you want better visibility and reliability out of your load balancing situation, so you throw haproxy into the mix:

Which works great. We ran this setup for a long time and were very happy with it. However, there are a few problems.

When actions take longer than 60s to complete, Mongrel will try to kill the thread. This has proven unreliable due to Ruby’s threading. Mongrels will often get into a “stuck” stage and need to be killed by some external process (e.g. god or monit).

Yes, this is a problem with our application. No action should ever take 60s. But we have a complicated application with many moving parts and things go wrong. Our production environment needs to handle error