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.

8 thoughts on “IIS7 on Windows Server 2008 – 503 Service Unavailable Error – Application Pool Stops Unexpectedly”

  1. Do you see any events in the System or Application event log? You should see evetns for each WP crash in the Application log, and an event in the System log if WAS suffers a communication failure with the worker process.

    The reason why your application pool will not restart likely have to do with Rapid Fail Protection – a feature, that by default stops your application pool if a worker process in it fails more then a specified number of times over a specified period of time (default: 5 times in 5 minutes).

    You can work around it by changing your RFP settings – highlight apppool in Inetmgr.exe, Advanced Settings task, change Failure Interval and Maximum Failures settings.

    But, you should really get to the bottom of why your WP crashes, and the event log should be the first stop.



  2. Even though after making the Start Automatically option to True then also the application pool is getting stopped. The server has ASP.NET 1.1 and 2.0 and 3.5

  3. I have the same problem. I have about 6 web sites on Web Server 2008 and the main one will occasionally just stop working. I have seen it produce an Error 503 to the client browser but usually absolutely nothing.

    I have scoured all the event logs and there are no events triggered whatsoever. Cycling the web site does not work, I have to reboot the whole server. This is getting very frustrating!


  4. I’m no expert, but I had a similar issue:

    Scroll down the list a little further of the pool’s basic settings.

    Do you see something called ‘Rapid Failure protection’? This shuts down the pool if a set number of processes fail within a set amount of time.

    Perhaps this is causing your shutdown, as one would imagine this would ignore the ‘Restart’ setting you mention.


  5. i am having same issue.
    As carl said, ther are some processes which are faling causing pool to stop.
    Can anybody explains which are those?.

    Your help be much appreciated, i m now very much frustrated.

  6. hurrey
    i got it resolved.
    In my case, i have installed some http handlers that was causing problem to run request on iis with ,net standard handlers.
    So, i uninstalled my custom handlers and my iis with app-pools running now.

  7. I believe this is a result of rapid fail protection. What we did was wrote a small script that sits on the server and restarts applications pool if/when they stop.

    You want the app pool to restart for garbage collection if it is being stopped for some reason by the server.

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