The following Windows update (see things to check) causes the ClarityWebAppPool and the ClarityWebServicesAppPool to fail to stay running.

Symptoms

• When accessing the web portal you get a 503 error Service Unavailable
• Web app pools above will not stay started.

Things to Check

• Were any Windows Updates installed?
  • Update for Microsoft Windows (KB4601555)
    • May 11, 2021-KB4601555 Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 10, version 1809 and Windows Server, version 2019 (microsoft.com)
  • Security Update for Microsoft Windows (KB5003243)
    • KB5003243: Servicing stack update for Windows 10, version 1809: May 11, 2021 (microsoft.com)
  • 

Event Logs

System Event Warning WAS Event 5021:

The identity of application pool ClarityWebAppPool is invalid. The user name or password that is specified for the identity may be incorrect, or the user may not have batch logon rights. If the identity is not corrected, the application pool will be disabled when the application pool receives its first request. If batch logon rights are causing the problem, the identity in the IIS configuration store must be changed after rights have been granted before Windows Process Activation Service (WAS) can retry the logon. If the identity remains invalid after the first request for the application pool is processed, the application pool will be disabled. The data field contains the error number.

Resolution

To resolve the issue add the App Pool identity used for Clarity to the Log on as batch job User rights assignment.  If the identity is part of a group policy you will need to add it to that then in an admin command prompt run gpupdate.  A reboot may be necessary.