Simplest way to redirect user to maintaining page

Just add an HTML file named “app_offline.htm” to the root directory of your website. Adding this file will clear the server cache. When ASP.NET sees the app_offline.htm file, it will shut-down the app-domain for the application (and not restart it for requests), and instead send back the contents of the app_offline.htm file in response to all new dynamic requests for the application.

The size of the file should be more that 512 bytes to be displayed.