IIS 7.0 Components

IIS7 contains several components that perform important functions for the application and Web server roles in Windows Server® 2008. 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.

By default, IIS7 provides HTTP.sys as the protocol listener that listens for HTTP and HTTPS requests. HTTP.sys was introduced in IIS 6.0 as an HTTP-specific protocol listener for HTTP requests. HTTP.sys remains the HTTP listener in IIS7, but includes support for Secure Sockets Layer (SSL).

To support services and applications that use protocols other than HTTP and HTTPS, you can use technologies such as Windows Communication Foundation (WCF). WCF has listener adapters that provide the functionality of both a protocol listener and a listener adapter. Listener adapters are covered later in this document. For more information about WCF, see Windows Communication Foundation on MSDN.

Hypertext Transfer Protocol Stack (HTTP.sys)

The HTTP listener is part of the networking subsystem of Windows operating systems, and it is implemented as a kernel-mode device driver called the HTTP protocol stack (HTTP.sys). HTTP.sys listens for HTTP requests from the network, passes the requests onto IIS for processing, and then returns processed responses to client browsers.

In IIS 6.0, HTTP.sys replaced Windows Sockets API (Winsock), which was a user-mode component used by previous versions of IIS to receive HTTP requests and send HTTP responses. IIS7 continues to rely on HTTP.sys for HTTP requests.

HTTP.sys provides the following benefits:

World Wide Web Publishing Service (WWW service)

In IIS7, functionality that was previously handled by the World Wide Web Publishing Service (WWW Service) alone is now split between two services: WWW Service and a new service, Windows Process Activation Service (WAS). These two services run as LocalSystem in the same Svchost.exe process, and share the same binaries.

Note   You may also see the WWW Service referred to as W3SVC in documentation.

How WWW Service works in IIS 6.0

In IIS 6.0, WWW Service manages the following main areas in IIS:

• HTTP administration and configuration
• Process management
• Performance monitoring

HTTP Administration and Configuration

WWW Service reads configuration information from the IIS metabase and uses that information to configure and update the HTTP listener, HTTP.sys. In addition, WWW service starts, stops monitors, and manages worker processes that process HTTP requests.

Performance Monitoring

WWW Service monitors performance and provides performance counters for Web sites and for the IIS cache.

Process Management

WWW Service manages application pools and worker processes, such as starting, stopping, and recycling worker processes. Additionally, WWW Service monitors health of the worker processes, and invokes rapid fail detection to stop new processes from starting when several worker processes fail in a configurable amount of time.

How WWW Service works in IIS 7.0

In IIS7, WWW service no longer manages worker processes. Instead, WWW Service is the listener adapter for the HTTP listener, HTTP.sys. As the listener adapter, WWW Service is primarily responsible for configuring HTTP.sys, updating HTTP.sys when configuration changes, and notifying WAS when a request enters the request queue.

Additionally, WWW Service continues to collect the counters for Web sites. Because performance counters remain part of the WWW Service, they are HTTP specific and do not apply to WAS.

Windows Process Activation Service (WAS)

In IIS7, Windows Process Activation Service (WAS) manages application pool configuration and worker processes instead of WWW Service. This enables you to use the same configuration and process model for HTTP and non-HTTP sites.

Additionally, you can run WAS without WWW Service if you do not need HTTP functionality. For example, you can manage a Web service through a WCF listener adapter, such as NetTcpActivator, without running the WWW Service if you do not need to listen for HTTP requests in HTTP.sys. For information about WCF listener adapters and hosting WCF applications in IIS7 by using WAS, see Hosting in WCF on MSDN.

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.

In the case of WCF, a listener adapter includes the functionality of a protocol listener. So, a WCF listener adapter, such as NetTcpActivator, is configured based on information from WAS. Once NetTcpActivator is configured, it listens for requests that use the net.tcp protocol. For more information about WCF listener adapters, see WAS Activation Architecture on MSDN.

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.

Process Management

WAS manages application pools and worker processes for both HTTP and non-HTTP requests. When a protocol listener picks up a client request, WAS determines if a worker process is running or not. If an application pool already has a worker process servicing requests, the listener adapter passes the request onto the worker process for processing. If there is no worker process in the application pool, WAS will start a worker process so that the listener adapter can pass the request to it for processing.

Note: Because WAS manages processes for both HTTP and non-HTTP protocols, you can run applications with different protocols in the same application pool. For example, you can develop an application, such as an XML service, and host it over both HTTP and net.tcp.

 

IIS 7.0 Modules

IIS7 provides a new architecture that is different from previous versions of IIS. Instead of keeping the majority of functionality within the server itself, IIS7 includes a Web server engine in which you can add or remove components, called modules, depending on your needs.

Modules are individual features that the server uses to process requests. For example, IIS uses authentication modules to authenticate client credentials, and cache modules to manage cache activity.

The new architecture provides the following advantages over previous versions of IIS:

• You can control which modules you want on the server.
• You can customize a server to a specific role in your environment.
• You can use custom modules to replace existing modules or introduce new features.

The IIS7 architecture also improves security and eases administration. By removing unnecessary modules, you reduce the server's attack surface and memory footprint, which is the amount of memory that server worker processes use on the machine. You also eliminate the need to manage features that are unnecessary for your sites and applications.

 

More info can be found on

 IIS.NET
 IIS TechCenter
 IIS Downloads
 IIS7 Community Forums
 IIS7 Team
 IIS7 Virtual Labs
 IIS7 Videos/Podcasts on Channel 9