AppPool is not enabled on server (HTTP 503)
Why the application pool of a website is stopped and how to start it again.
Your website returns HTTP Error 503 – Service Unavailable, and when you open it in the Control Panel you see Error! AppPool [siteXXXX] is not enabled on server or AppPool is disabled — although the website itself is shown as Enabled. The application pool that runs your website has been stopped on the server.
An application pool is stopped for one of a few reasons. Find yours below.
1. Our security system stopped the website
This is the most common cause. The application started a separate program on the server — typically Chrome or Edge through Puppeteer, Playwright or Selenium, FFmpeg, or another bundled executable — and the automated security system suspended the website.
What to do: open a support ticket, tell us the website and what the program is for. On the Free plan such tools are not allowed; on Premium we enable the website again and add an exception where possible. See Website disabled by the security system.
2. An app_offline.htm file was left behind
Web Deploy and some deployment scripts put an app_offline.htm file into wwwroot to stop the application during publishing. If the deployment is interrupted, the file stays there and the application does not start again.
What to do: connect over FTP or open the File manager, delete app_offline.htm from wwwroot, and click Restart application (AppPool) on the Process page. See Take the website offline with app_offline.htm.
3. The application crashes right after it starts
When a process crashes repeatedly within a short time, the web server stops the application pool to protect the server. The page then says HTTP Error 503.0 – Server has been shutdown or just Service Unavailable.
What to do: open Logs for the website and read the last entries before the stop. The usual causes are:
- a wrong
appsettings.jsonorweb.config— see HTTP Error 500.30 – the application failed to start, - the memory limit was reached again and again — see Increase the memory (RAM) of a website,
- in an ASP.NET Core application, the web host is built twice. Search
Program.csandStartup.csforCreateBuilder,CreateDefaultBuilder,ConfigureWebHostDefaultsandUseIIS: only one of them may be called, and only once. A second call ends the process with "503.0 – Server has been shutdown".
Fix the cause, publish again and click Restart application (AppPool). If the error is not clear from the log, turn on ASP.NET Core debug logging.
4. Server maintenance
After a Windows update or a maintenance window a website can briefly return 503 while the server is coming back. Check the service status page and try again in a few minutes.
Start the application pool again
Open the Process page
In the Control Panel go to Websites, open the website and choose Process.
Restart
Click Restart application (AppPool). The same button is on the Scripting page.
Still stopped?
If the Control Panel keeps showing AppPool is not enabled on server, the pool was stopped by our security system or by the server. Open a support ticket with the name of the website — we start it again and tell you why it was stopped.
Note
Every click on Restart is recorded in the website Logs as a restart initiated from the Control Panel. The entry "A process serving application pool 'siteXXXX' terminated unexpectedly … exit code 0xffffffff" that appears right after it is the result of your own restart, not a crash.