Documentation:IIS troubleshoot

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