What is an Application Pool?
An Application Pool can contain one or more applications and allows us to configure a level of isolation between different Web applications. For example, if you want to isolate all the Web applications running in the same computer, you can do this by creating a separate application pool for every Web application and placing them in their corresponding application pool. Because each application pool runs in its own worker process, errors in one application pool will not affect the applications running in other application pools. Deploying applications in application pools is a primary advantage of running IIS 6.0 in worker process isolation mode because you can customize the application pools to achieve the degree of application isolation that you need.
When you configure application pools for optimum availability, you also should consider how to configure application pools for application security. For example, you might need to create separate application pools for applications that require a high level of security, while allowing applications that require a lower level of security to share the same application pool. In the later part of this article, we will see how to configure identities at the application pool level.
Creating a new Application Pool
Creating a new application pool is a very simple process that is carried out by using the IIS manager. When you create a new application pool, you have the following two options:
You can either create a new application pool from scratch or
You can create a new application by importing the configuration settings from an external XML file
To create a new application pool from scratch, right-click on the Application Pools node from the tree view and select New->Application Pool from the context menu. You will be presented with the following screen, where you need to enter a name for the application pool.
When creating a new application, you also have the option of inheriting the settings from an existing application pool. For example, if you want your new application pool to inherit the settings from the DefaultAppPool, you can do that by selecting the option Use existing application pool as a template in the above screen. After you pick this option, the Application Pool name dropdown box will be enabled from where you can select an existing application pool.
After the pool is created, you can save the settings of the application pool to an external XML file any time by right-clicking the application pool and selecting the option All Tasks->Save Configuration to a File that is available from the context menu. This is an extremely useful feature that makes it possible for you to easily recreate the same application pool on the same server or on a different server with minimal effort.
