On a blank DMA installation we notice that the IIS DefaultAppPool is always automatically getting into a stopped state. This causes an HTTP 503 - Service Unavailable error to be shwon when acessing the web pages.
The Windows Event Viewer lists multiple of these entries:
A listener channel for protocol 'http' in worker process '17996' serving application pool 'DefaultAppPool' reported a listener channel failure. The data field contains the error number.
Which seem to trigger an auto-stop:
Application pool 'DefaultAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool.
Any idea what could cause this, or how to further debug?
Note that this started to occur after a 10.2 -> 10.3 main release upgrade. After further upgrading to 10.4.1 feature release the issue persists.
Agent is running on Windows Server 2022 Standard.
Because of IIS "Rapid-Fail Protection", since it reaches the maximum amount of failures within the configured interval, it will permanently shut down the application pool and manual action is needed.
From the error message, it looks like the application pool "DefaultAppPool" doesn't start up anymore. This can have several reasons:
- Corrupt installation
- Installation of modules which are activated but do not start for some reason (either those modules are missing or lack dependencies)
- Lack of file system permissions, IIS isn't able to for example read the web folder or ApplicationHost.config file
Going from 10.2 to 10.3, I would think something went wrong when installing newer .NET versions, or something went wrong in combination with a version that was already installed.
Finding the root cause could take up a lot of time, it might often be easier to revert a backup or to wipe the system and reinstall the Windows Server OS.