The maximum number of requests an application pool can process for each IIS 8.5 website must be explicitly set.
IIS application pools can be periodically recycled to avoid unstable states possibly leading to application crashes, hangs, or memory leaks. By default, application pool recycling is overlapped, which means the worker process to be shut down is kept running until after a new worker process is started. After a new worker process starts, new requests are passed to it. The old worker process shuts down after it finishes processing its existing requests, or after a configured time-out, whichever comes first. This way of recycling ensures uninterrupted service to clients.
Open the IIS 8.5 Manager. Click on the “Application Pools”. Highlight an Application Pool and click "Advanced Settings" in the “Action” Pane. Scroll down to the "Recycling section" and set the value for "Request Limit" to greater than "0". Click “OK”.
Note: Recycling Application Pools can create an unstable environment in a 64-bit SharePoint environment. If operational issues arise, with supporting documentation from the ISSO, this check can be downgraded to a Cat III. Open the IIS 8.5 Manager. Perform for each Application Pool. Click the “Application Pools”. Highlight an Application Pool and click "Advanced Settings" in the “Action” Pane. Scroll down to the "Recycling section" and verify the value for "Request Limit" is set to a value other than "0". If the "Request Limit" is set to a value of "0", this is a finding.