Turnkey Not Starting

If your Turnkey application does not start in IIS, follow these guidelines to pinpoint the problem area:

In the Turnkey web.config file, remove the section that makes the errors route into the application:

<httpErrors errorMode="Detailed" >
</httpErrors>

If you do not replace this, some errors will be rerouted into the same situation that has the problem.

Make sure you have:  

<system.web>
  <compilation debug="true" />

• Advanced settings for AppPool* (to consider)

Specific time, same every day

Allow overlap AppPool recycle must be disabled.

Idle time-out action Suspend AppPool (not terminate)

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ServerSidejobs or SysAsyncTickets being re-entered and started in parallel, or VistaDB is locked by another process :

Understanding IIS Restarting and Process

External good article on how IIS works internally and how to handle restarting it: https://www.leansentry.com/guide/reset-restart-recycle-iis