A website hosted in Plesk fails to load with 503 error: Application pool 'example.com is being automatically disabled due to a series of failures in the process(es) serving that application pool.

Symptoms

• A website is unavailable with the following error:

  PLESK_INFO: 503. The service is unavailable.

• After starting the application pool of this site in IIS, the application pool then stops randomly within a specified time period. One of the following error messages is logged in Event Viewer > Windows Logs > Application:

  PLESK_INFO: Application pool 'example.com is being automatically disabled due to a series of failures in the process(es) serving that application pool.

  ---

  PLESK_INFO: An unhandled exception occurred and the process was terminated.
  ...
  Message: One or more errors occurred.

Cause

Rapid-fail protection (IIS feature) automatically disables application pool, if it crashes several times within a specified time period (5 failures in 5 minutes by default).

Resolution

Note: Rapid-fail protection prevents the failing application pool from getting into a continuous loop of crashing. This is useful when an application goes out of control which could overload the server.
In general, it is better to review the application code to resolve crashes.

To prevent an application pool from stopping, disable rapid-fail protection in IIS. Refer to these articles for more information:

1. Connect to your Plesk server via RDP.
2. Start Internet Information Services (IIS) Manager at Windows Start > All Programs > Windows Administrative Tools.
3. In IIS Manager, go to SERVER_NAME > Application Pools > example.com > Advanced Settings.
4. Scroll down to Rapid-Fail Protection and change the option Enabled from True to False.

5. Click OK to apply the changes.