The most significant changes within the new architecture for IIS 6.0 are:
- a new process model called WPIM ( Worker Process Isolation Mode)
- Application Pooling and Recycling
- HTTP.SYS - it is a HTTP listener that is a kernel mode driver and is a common endpoint for HTTP traffic on the platform
- WWW Service Administration and Monitoring (W3ADM). It is part of the WWW Service.
- the IIS Metabase is in XML format
Below you will see how a HTTP request is processed by HTTP.SYS and passed onto the IIS architecture components.
When an HTTP request arrives at the kernel-mode HTTP Listener/Endpoint, it checks the validity of the request. If the request is invalid, the appropriate HTTP error is immediately returned to the requester. If the request is valid, HTTP.sys checks to see if it can handle the request from its cache. If the response is in the cache, HTTP.sys sends the response immediately. Otherwise, HTTP.sys puts the request in a separate request queue for each worker process (application).If the necessary worker process is not listening on the request queue, then HTTP.sys signals the W3ADM to start and configure a worker process based on the configuration information stored in XML format in the metabase.
If a worker process or a group of worker processes (called a Web garden) is already started and connected to the request queue, the worker process pulls the request from the queue, processes it through any ISAPI filter or extension and Web application code, and returns the response to the HTTP.sys and the requester.
The W3ADM also monitors the health of a worker process and if, for example, the process does not respond or has exceeded a threshold (e.g., the number of hours running or number of requests handled), WAS coordinates with the HTTP Listener to hold requests in the queue while W3ADM stops the worker process and restarts it.
