ASP.NET 2.0: Strange 404 Errors and the "App_Offline.htm" file

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If you get strange HTTP 404 errors in your ASP.NET 2.0 application, always check for a zero-length "magic file" called app_offline.htm and delete it. If this file is present in your web site, then the entire application will be considered offline by the ASP.NET runtime. There is actually a button that says "Take application offline" which creates this file, but unfortunately the "magic file" can also "magically appear", so you can spend quite some time chasing bugs that aren't there. Post-beta 2 builds are expected to provide a proper explanation.

The reason it can appear by itself is that it's used to "take the application offline" when copying a web site. If this operation crashes somewhere in the middle for some reason, the file doesn't get deleted. For ADO.NET and Databases, if ASP.NET has open connections, you can shut down the application domain by adding a file named "app_offline.htm" to the Web application root directory. This has the effect of shutting down the application domain (not the process) and redirecting all requests to the application to this file (returning a 404 response code).

To allow the application to restart, remove this file. Note that simply closing connections in your page code will not release the file lock, because by default the ADO.NET connection pool retains the active connections.
Peter has been active on the C# and other MS newsgroups, has had samples at gotdotnet.com (now codegallery.com) that have been downloaded over 56,000 times, and has written numerous articles for eggheadcafe.com, for which he is a co-founder, and MSDNAA sites. He has also been a technical reviewer on books from Prentice Hall, Manning and other publishers. Peter was a Microsoft MVP for 10 years. Peter was born and raised in New York City, and after a stint as a jazz musician playing contrabass with the Robert Hunt Trio, migrated to sunny Florida, where he was hired as a rookie Financial Consultant at Merrill Lynch in Orlando, specializing in Corporate Services. It was at Merrill that Peter realized computers and technology were his forte. He spent his last few years at Merrill developing real – time computerized trading and and stock charting program using advanced technical analysis indicators, some of which are his own inventions. In 1997, he moved on to architect and serve as lead developer on a number of innovative web-based and middleware solutions for the healthcare and financial services industry.

Comments

  1. Anonymous1:52 PM

    I have the same problem except that I do not have any app_offline.htm pages in my harddisk. I have even looked at the the hidden files and I am unable to locate it.
    The best part is that the application was just working fine until yesterday.Do you have any ideas on why I still have that error?

    Thanks.

    ReplyDelete

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