How to prevent IIS from shutting down Web Site when not in use?

Question

I have a web application hosted under IIS. It is a data warehouse, and during its startup process it requires instantiating a large set of items in memory (takes roughly ~20 minutes to fully set up). Because this website is critical to our company, this system must be online 100% during the daytime, and only can be restarted during off-work hours.

For some reason, this web application seems to be "offline" when there is no usage for some time. I know this because the cache is not fully instantiated when the website is visited. This is unacceptable.

It is not clear to me why the website is shut off. The application pool is only set to recycle daily at 4:00 AM (it is 11 AM now).

Are there other settings which I'm not aware of on the IIS part that causes it to shut down the website automatically?

Addl Note: The website does not shut off automatically when running in IISExpress in Visual Studio. Only the production version hosted on IIS shuts off.

Here's a screen of the Advanced Settings for the Application Pool the web site is running under. (Not sure if it's useful.)

I'm on IIS 7.5, Server 2008 R2. It is an ASP.NET 5 Web App.

Answer 1

Check Idle Time-out settings under process model in screenshot. That setting is causing app pool shutting down when remain idle for 20 mins. You can set it to 0 to keep it running all time even when its idle i.e. not processing any requests.

Note: Keeping app pool running all time will consume server's precious memory. It may become critical especially if application is leaking memory.