How to Make your ASP.NET 2.0 Application Unavailable

Create HTML file and name it app_offline.htm then place this file into the root of the application.

When ASP.NET finds it, it will shut-down the app-domain and will stop all requests. and will send back the contents of the app_offline.htm file in response to all new dynamic requests for the application. and to enable the site again just delete or rename the file and the site will come back online automatically.