Internet Information Services


 Internet Information Services (IIS) 7 and later provide a request-processing architecture which includes:

  • The Windows Process Activation Service (WAS) which enables sites to use protocols other than HTTP and HTTPS.
  • A Web server engine that can be customized by adding or removing modules.
  • Integrated request-processing pipelines from IIS and ASP.NET.

Components in IIS

 IIS contains several components that perform important functions for the application and Web server roles in Windows Server. Each component has responsibilities, such as listening for requests made to the server, managing processes, and reading configuration files. These components include protocol listeners, such as HTTP.sys, and services, such as World Wide Web Publishing Service (WWW service) and Windows Process Activation Service (WAS).

Protocol Listeners

 Protocol listeners receive protocol-specific requests, send them to IIS for processing, and then return responses to requestors. For example, when a client browser requests a Web page from the Internet, the HTTP listener, HTTP.sys, picks up the request and sends it to IIS for processing. Once IIS processes the request, HTTP.sys returns a response to the client browser.

Windows Process Activation Service (WAS)

 Windows Process Activation Service (WAS) manages application pool configuration and worker processes instead of the WWW Service. This enables you to use the same configuration and process model for HTTP and non-HTTP sites.

Configuration Management in WAS

 On startup, WAS reads certain information from the ApplicationHost.config file, and passes that information to listener adapters on the server. Listener adapters are components that establish communication between WAS and protocol listeners, such as HTTP.sys. Once listener adapters receive configuration information, they configure their related protocol listeners and prepare the listeners to listen for requests.

The following list describes the type of information that WAS reads from configuration:

  • Global configuration information
  • Protocol configuration information for both HTTP and non-HTTP protocols
  • Application pool configuration, such as the process account information
  • Site configuration, such as bindings and applications
  • Application configuration, such as the enabled protocols and the application pools to which the applications belong

If ApplicationHost.config changes, WAS receives a notification and updates the listener adapters with the new information.

Application Pools in IIS

 Application pools separate applications by process boundaries to prevent an application from affecting another application on the server. In IIS 7 and later, application pools continue to use IIS 6.0 worker process isolation mode. In addition, you can now specify a setting that determines how to process requests that involve managed resources:

  •  Integrated mode
  •  Classic mode

Integrated application pool mode

 When an application pool is in Integrated mode, you can take advantage of the integrated request-processing architecture of IIS and ASP.NET. When a worker process in an application pool receives a request, the request passes through an ordered list of events. Each event calls the necessary native and managed modules to process portions of the request and to generate the response.

There are several benefits to running application pools in Integrated mode. First the request-processing models of IIS and ASP.NET are integrated into a unified process model. This model eliminates steps that were previously duplicated in IIS and ASP.NET, such as authentication. Additionally, Integrated mode enables the availability of managed features to all content types.

Classic application pool mode

 When an application pool is in Classic mode, IIS 7 and later handles requests in the same way as in IIS 6.0 worker process isolation mode. ASP.NET requests first go through native processing steps in IIS and are then routed to Aspnet_isapi.dll for processing of managed code in the managed runtime. Finally, the request is routed back through IIS to send the response.

This separation of the IIS and ASP.NET request-processing models results in duplication of some processing steps, such as authentication and authorization. Additionally, managed code features, such as Forms authentication, are only available to ASP.NET applications or applications for which you have script mapped all requests to be handled by aspnet_isapi.dll.