Some time you need to change/update database or update back end services or just shut down the application. During this activity you need to make your application offline. So, no user can access your web application during this activity.
app_offline.htm file make your work easier. This is very quick solution to make your application offline.
Create html file named app_offline.htm and write some custom message into the file just like ‘Application is down due to maintenance’. Place this file in the root directory of your application. As soon as you place file, application will be made offline to users and will show content of the app_offline.htm file for all the requests. Also the application will shut down and application domain will be unload from the server.
Existing request to the application will continue as it is. Only new request to the application will get the content of the app_offline.htm file.