OS: Windows Server 2008 R2
No Managed Code
I am trying to nail down the issue here. I am not sure if it was precipitated by some change from a group policy (I don't have any control over that) or from installing some Windows Update.
All of a sudden after a reboot, none of my sites would work, they all respond with
HTTP Error 503. The service is unavailable. The app pools were stopped and there are 5 warnings (EventID 5009, EventSourceName WAS) and 1 error (EventID 5002, EventSourceName WAS) in the System event logs and 5 errors (EventID 2276, EventSourceName W3SVC-WP) in the Appliation event logs (per app pool).
I switched all my sites to a single app pool and change the identity to NetworkService and they all work. This however seems like a security/scale issue?
I downloaded DebugDiag 2 and tried to get a dump, however it never seemed to trigger. I also try to find the process in Process Explorer, but any app pool not using the NetworkService identity doesn't show up.
I don't know how else to look for the root cause.
EDIT @Lex Li
Checked my Debug Tool log and found this
[7/19/2018 3:29:02 PM] New process found: Process Name - w3wp.exe Process ID - 4652 Process Identity - IIS APPPOOL\Test Pool Web application pool name - Test Pool
[7/19/2018 3:29:02 PM] Attach Debugger: Process Name - w3wp.exe Process ID - 4652 Control Script - C:\Program Files\DebugDiag\Scripts\CrashRule_WebAppPool_Test Pool.vbs
Error Code - 0x80070002
Error Source [DbgSvc.Controller.1]
Error Description 
Line 93, Column 2
[7/19/2018 3:29:03 PM] Process Exited: Process Name - w3wp.exe Process ID - 4652 Web application pool name - Test Pool
However that only shows up once, and can't reproduce it.