Taking an ASP.NET Site Offline with a Message
This was another one that I was literally beside myself that I didn't know this one before. A fellow business partner of mine named James Sutton mentioned this one to me. This one's been around since ASP.NET 2.0 as well. If you have an ASP.NET web application site, and you place a text file named "app_offline.htm" in the root of the site, all requests to that website will redirect to that app_offline.htm file. Basically, if you need to take an entire ASP.NET site offline, you can place some nice message in that file. Then, any new requests to a URL, any URL, in that website will redirect to that file allowing you to do maintenance to the site, upgrades, or whatever. It is not really a redirect though. ASP.NET essentially shuts down the site, unloads it from the server, and stops processing any requests to that site. That is, until you delete the app_offline.htm file - then things will continue as normal and your ASP.NET site will load up and start serving requests again.
A super-cool side effect of this is that any files that are locked by the site, such as a database or other resources, are freed since the application domain has been unloaded from the server. This allows you to remove the locks from those files and replace them, without the need to do a full IISRESET, taking down other sites on the server. One thing to keep in mind with this file however, make sure you out enough content in it so it is larger than 512 bytes or IE will consider it a 404 and will display the 404 instead of the contents of your app_offline.htm file.
Thanks to Ryan Farley for posting this tip...