I decided to add this post in hopes that it helps someone avoid the 6 plus hours of troubleshooting I recently went thru before solving the problem described by the subject of this thread.
BLOT (Bottom Line on Top):If your web application suddenly stops responding to you for no apparent reason and returning 503s, check the application root to see if a file called app_offline.htm has appeared there. If you see this file, delete it with extreme prejudice! Its presence is a signal to IIS to stop loading an app domain and return 503 - Service Unavailable.
As soon as I removed the file, my web app started functioning perfectly again.
I'm reminded of a line from a Disney movie, "The Emperors New Groove", in which Yzma asks the dimwitted Kronk, "Why do we even have that lever?!?" after being dropped thru a trapdoor into a crocodile infested moat. ;-)
How did it get there?
My machine had just experienced a BSOD, caused by (I'm pretty sure) the interaction of TFS 2010 Power Tools and my companies aging TFS 2005 server instance. This had actually happened to me several times over the past couple months, but I've been extremely busy and had not taken the time to deal with the BSODs.
From what I gather, IIS itself or the visual studio tooling occasionally creates this file, app_offline.htm, to synchronize operations. Given that I have never encountered this before in several years working with visual studio and IIS, I assume whatever process this is normally just takes care of itself. By pure dumb luck, the BSOD must have occurred at just the right moment to cause the file to be left out there.
Well, Lesson learned. If such experiences are good for nothing else, they usually serve to sear the particular problem and solution into my brain. This'll be the first thing I look for next time!
Hope this is helpful to someone,
Pertinent Software profile:
- Windows 7 Enterprise / IIS 7.5
- Visual Studio 2010 Ultimate
- TFS 2010 Power Tools
- TFS 2005 Server