As you all now, many of us as a website owners or a web administrators may need to do some maintenance to their websites.
Many of you may just edit web.config or edit a default page to load a maintenance page like saying eg Sorry this website is under maintenance.
Beside the above, there is one simple way you can do which is to create a file called app_offline.htm and upload it to web root folder. Visitors will see the message while you are upgrading the website.
The App Offline file (app_offline.htm) is used by the ASP.NET Core Module to shut down an app or website.
If a file with the name app_offline.htm is detected in the root directory of an website, the ASP.NET Core Module attempts to gracefully shut down the app and stop processing incoming requests.
If the app is still running after the number of seconds defined in shutdownTimeLimit, the ASP.NET Core Module stops the running process.
While the app_offline.htm file is present, the ASP.NET Core Module will ignore all existing web.config settings or any existing IIS settings.
Thank you