IIS Process Recycling

Question

I have read the MSDN article (link) which says something about the IIS process recycling and it turns out that

The new process is started before the old worker process stops, and requests are then directed to the new process.

But, when I read next part of that article i saw this:

Occurrence of multi-instancing: In multi-instancing, two or more instances of a process run simultaneously. Depending on how the application pool is configured, it is possible for multiple instances of a worker process to run, each possibly loading and running the same application code. The occurrence of an overlapped recycle is an example of multi-instancing, as is a Web garden in which two or more processes serve the application pool regardless of the recycling settings.

If your application cannot run in a multi-instance environment, you must configure only one worker process for an application pool (which is the default value), and disable the overlapped recycling feature if application pool recycling is being used.

So, I am a little confused.

On the one hand, I am okay with the thing when all the web requests immediately and permanently are become directed to the new process instance. On the other hand, this article recommends me not to use recycling at all in case if my application, quoting above "cannot run in a multi-instance environment". Which means, in my opinion, that requests may be processes as one or the other process instance, which is not allowed by my app logic.

All I want to know is, if there is any chance, any opportunity, that IIS can go such bad way and collapse my application, or shouldn't I worry about it?

Answer 1

IIS by default will recycle periodically; this is normal and healthy behavior (frees up system resources). IIS will only run multiple processes for the same app temporarily. On a recycle the new process will start and the original will only run until current activities have completed or the timeout period has expired. If you're concerned about session state, look into State Server (SQL being the preferred method). I've got a couple posts regarding this very issue, but check out this link.