IIS7 on Windows Server 2008 – 503 Service Unavailable Error – Application Pool Stops Unexpectedly

So twice now, I’ve had a problem where an IIS7 Application pool unexpectedly stops and does not restart itself, and it does not put any events in the event log that help to track the root of the problem. On a server that runs about 20 different websites, all other sites continue to function normally, it has just been 1 site, on 3 different occassions now that ceases to run. For some reason, it just stops, and when looking at the application pool list, it has a stopped icon next to it:

IIS 7 Application Pools Listing

There is an option under the “Advanced Settings” – just right click on the application to get there. Select Advanced Settings and you’ll be presented with a screen that looks like this:

IIS7 Application Pool Advanced Settings

Apparently, if you set the Start Automatically option to True your application will restart if it crashes, but this hasn’t been the case for me. Each time my application has crashed (with the Start Automatically option set to True) the application hasn’t restarted on its own, I’ve had to login to the server remotely to restart the application.