Updated on Kisan Patel
Application Pool Stops automatically.
503 Service Unavailable when not using default application pool.
Application Pool automatically stop due to a series of failures.
Rapid-Fail Protection disables application pool if it crashes several times within in a specified time period.
To prevent an Application Pool from stopping, you can disable Rapid Fail Protection in IIS:
Open Internet Information Services (IIS) Manager > Application pools > choose application pool > Advanced Settings.
Scroll down to Rapid Fail Protection and change the option Enabled from True to False. Click OK to apply the changes.