What is IIS application pool Idle Timeout Action?

Starting in IIS 8.5, the application pool idle process capability was extended.  In prior versions, the worker process  had an idle timeout property.  When the idle timeout was configured, a worker process will shut down after a specified period of inactivity, by default 20 minutes. 


What happened when that boundary was hit was that the worker process was terminated.  The session would be terminated.  This killed the session and the user would be forced to start over.  This is an issue for a customer who tends to have long web sessions.


The idle process capability provides the ability to override the default terminate behavior.  The property is either terminate (default) or suspend.  A suspended worker process remains alive but is paged-out to disk, reducing the system resources it consumes. When a user accesses the site again, the worker process wakes up from suspension and is quickly available. When an idle worker process is terminated, the worker process is shut down and the startup period will be longer when the site is subsequently accessed. The default behavior is to terminate the idle worker process, and the same behavior is used in the previous versions of IIS.

Source:

https://www.youtube.com/watch?v=hkizFsHDexA
https://nimitsharma.wordpress.com/2014/10/03/introducing-iis-application-pool-idle-timeout-action/