Types of Windows Application Pools

 The configuration settings for all application pools running on the Internet Information Service (IIS) 7 are the main elements of an application pool. Application pools contain one or more worker process. Application pool is assigned with the common settings, which are used to serve for one or more requests. The worker process are then configured and assigned to the application pool. The isolation from one web application from another web application is achieved because of the application pool, which allows the web applications to share one or more similar configured worker process. Any error in one application pool does not affect websites or applications in another application pool. This is implemented by the boundaries set for the process of each worker process.

In IIS 7 and later, each application pool uses one of two .NET integration modes for running ASP.NET applications: Integrated or Classic. The .NET integration mode defined for the application pool determines how IIS processes an incoming request to the sites, applications and Web services that run in that application pool.

Integrated

Integrated mode is the default mode by which all the application pools in the IIS 7 and later runs. This mode allows all the ASP.NET modules to be a part in IIS request process without checking the type of resource requested. In this integrated mode all the features of the ASP.Net 2.0 request pipeline are made available to the requests for static content, as well as ASP, PHP, and other content types.

Classic

In Classic mode the asp.net applications are hosted by the IIS 6.0 processing pipe line. In this mode, The ASP.NET requests are processed first through the IIS 7 and later modules. Also ASP.NET requests are then processed by the aspnet_isapi.dll. The IIS 7, later processing pipe lines, and the ASP.NET pipelines are separate from each other. The other resource types do not get the features of the ASP.NET request processing pipelines. This indicates the fact that ASP.NET request should undergo through authentication and authorization modules in both process models. However, Classic mode is not as efficient as integrated mode. Classic mode is not compatible with applications that were developed using ASP.NET version 1.1 on an IIS 7 and later server. It cannot be ran without modifying the application in integrated mode.

The Application Pool Identity type is a feature in new IIS 7.5 and above editions, which is used for identity attribute of the <processModel> element. This process identity feature is a default for applications, and allows to secure the content areas to allow a specific application pool. This security feature can be enabled using the name of an application pool by using syntax “IIS AppPool\DefaultAppPool.” The surface attack area of the server is reduced severely because the identity feature is created dynamically.