Welcome to the passenger wiki!
A Problem with Passenger: after running for a period of time, Passenger stops working, producing an error log entry of: “* Unexpected error in Passenger: The ApplicationPool server exited unexpectedly.” for each request. Nothing shows up in the Rails log. Others have reported this as well.
The workaround is to restart apache with “apache2ctl graceful”, which works perfectly.
In my case, I have a very low traffic site and I want to keep at least one passenger thread ready. Therefore, the passenger threads do not exit, as I have set PassengerPoolIdleTime to be greater than the interval between hits. There does not seem to be any way to indicate the maximum number of requests to be handled by a thread before it exits, which would probably be the correct solution.
I apologize if this is not the correct place for a bug report/feature request, but I did not see anywhere else to post this.