Corrupt Session?

The system that I have been working on for the past while had a particularly vexing problem. Every morning, I had to restart the mongrel cluster. The reason, each morning the login process just stopped working. It was especially annoying, because I had one shot each day to attempt to fix it (to apply the fix, I had to restart the server). After a two weeks of various attempts at correcting the problem, we finally stumbled upon the problem.

class ApplicationController < ActionController::Base
  session :session_expires => 12.hours.from_now
end

I was assuming that a session would gracefully expire 12 hours after first being created. In fact, what was happening is the session would expire 12 hours after the server restarted. So once twelve hours would pass, each request would generate a new session that would in essence be immediately expired. Not exactly the behavior I was looking for.

So if you are looking for corrupt session, session corruption, or unresponsive mongrel it may just be related to the code above.