So you have a cool asp.net application and everything is running great. You're running it under NET 2.0 and you're using a report server on the same machine. It may run great for months, and then out of nowhere your web application starts displaying the “Service unavailable” page. It does this until you do an iisreset. Where did this message come from? I recently had to find out for myself. My search lead me to the Event Viewer on the server and five warnings about various system failures that read something like this:

A process serving application pool 'ASP.NET V2.0' suffered a fatal communication error with the World Wide Web Publishing Service.

After the fifth warning I would get the following error:

Application pool 'ASP.NET V2.0' is being automatically disabled due to a series of failures in the process(es) serving that application pool.

After the iisreset, things would go OK, but eventually the above warning/error pattern would repeat. What was going on? Why five warnings, the single error, and then the “Service unavailable” page? Well, when you search for "Application pool 'ASP.NET V2.0' is being automatically disabled due to a series of failures", you get plenty of hits. There are plenty of ways to get these errors. What I ended up finding out was that my report server and my web application were using the same application pool. I would not think this would be a big deal, until I found this tab in the properties of the application pool within the IIS Manager.

Mystery solved. It was doing exactly what it was supposed to do. The Enable rapid-fail protection was enabled and I had gotten five failures within 5 minutes to cause the application pool to be disabled. Let's say your web application calls for a report from your reports server. If your reports server fails for some reason, you can also get a failure with your web application. Since they are both in the same application pool this is two strikes with one failure. A couple more of these and your application pool gets shut down. Lesson Learned. It's good practice to move the web application and reports servers into their own application pools.