An application pool is technically not a part of the site/application/ virtual directory, but it is an important part of configuring the server to be able to serve requests to the application.
Many websites can be in the same application pool. At least one application pool defines the settings for a worker process that will host one or more IIS 7 application.
The application pool is a unit of process isolation since all request processing for an application runs within its application pool’s worker processes.
This is also a unit of isolation from a security point since the application pool can run with a different identity, And
ACL all needed resources exclusively for itself to intercept applications in other application pools from being able to access its resources.
Create an Application Pool:
a. Right-click on Application Pools and click on Add Application Poll.
b. After clicking Add Application Poll… the Add Application Pool dialog box will appear.
c. Then press OK.
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