Web Garden:-

By default, each application pool runs with a single worker process (W3Wp.exe). We can assign multiple worker processes with a single application pool. An application pool with multiple worker processes is called a Web Garden. Many worker processes with the same Application Pool can sometimes provide better throughput performance and application response time. And each worker process should have its own Thread and memory space.

As shown in the picture, in IIS, there may be multiple application pools and each application pool will have at least one worker process. A Web Garden should contain multiple worker processes.

There are certain restrictions in using a Web Garden with your web application. If we use the InProc session mode, our application will not work correctly because the session will be handled by a different worker process. To avoid this problem, we should use the OutProc session mode and we can use a session state server or SQL-Server session state.

Main advantage: The worker processes in a Web Garden share the requests that arrive for that particular application pool. If a worker process fails, another worker process can continue processing the requests.

How to Create a Web Garden?

Right click on Application Pool > Go to Performance tab > Check Web Garden section (highlighted in picture):

By default, it would be 1. Just change it to more than one.

How Session depends on Web Garden?

I have already explained that InProc is handled by a worker process. It keeps data inside its memory object. Now if we have multiple worker processes, then it would be very difficult to handle the session because each and every worker process has its own memory, so if my first request goes to WP1 and it keeps my session data and the second request goes to WP2, I am trying to retrieve session data and it will not be available, which will throw an error. So please avoid Web Gardens in InProc session mode.

We can use StateServer or SQLServer session modes in Web Gardens because as I have already explained, these two session modes do not depend on worker processes. In my example, I have also explained that if you restart IIS, you are still able to access your session data.

In short: