Checklist: Understanding IIS 6 Architecture

The following is a checklist of essential concepts associated with the architecture of IIS 6. Read each one and check them off after you’re sure you understand the significance of the concept because future chapters will make frequent use of them as you learn how to perform various IIS administrative tasks:

• http.sys, the Kernel Mode HTTP Listener, is responsible for handling incoming HTTP requests.

• Kernel mode queuing allows HTTP requests to be queued until the appropriate worker process can handle them.

• The IIS Admin Service (inetinfo.exe) manages the FTP, SMTP, and NNTP Services but not HTTP.

• Web applications can no longer be hosted in-process within inetinfo.exe.

• The Web Administration Service (WAS), a new component of the WWW Publishing Service (W3SVC), is responsible for managing the health of worker processes and maintaining the metabase.

• Instances of W3SVC (and hence the WAS) run as a DLL within a host process called svchost.exe.

• Worker processes are implemented as instances of the executable w3wp.exe and can host ISAPI applications and filters, ASP applications, CGI applications, and static web content.

• Using processor affinity, a worker process can be assigned to a specific processor on a symmetric multiprocessing (SMP) machine.

• All applications running on IIS 6 run within application pools, which consist of one kernel mode http.sys request queue and one or more worker processes.

• An application pool can host one or more applications running within it.

• A web garden is an application pool served by multiple worker processes.

• Demand Start allows applications to be loaded on-demand into their application pool when the first HTTP request for the application is received.

• Idle Timeout allows a worker process to be shut down to save memory if the application using it has not been used for a period of time.

• Process recycling allows worker processes to be restarted periodically to support applications that have memory leaks or other problems.

• Orphaning allows IIS to kill hung worker processes and start new ones to replace them.

• Rapid fail protection lets an application pool be switched to out-of-service if it fails frequently.

• Worker process isolation mode is the mode supporting new IIS 6 features such as worker processes, application pools, web gardens, and so on.

• IIS 5 isolation mode is an alternative IIS 6 mode to ensure compatibility with legacy applications that will not run properly in worker process isolation mode.