Managing Application Pool Health

Applies To: Windows Server 2003, Windows Server 2003 with SP1

IIS 6.0 health-monitoring and management features support application availability by detecting problems with worker processes that are assigned to application pools, and by taking action to manage the problems. When IIS 6.0 is running in worker process isolation mode, you can detect the health condition of a specific application pool by enabling the WWW service to ping a worker process that is assigned to it. Also, you can set features to take corrective action when an unhealthy condition occurs.

Generally, a healthy worker process responds to periodic pings that are sent by the WWW service. If a worker process does not respond to the pings within the time interval specified by the PingResponseTime property, the WWW service determines the worker process to be unhealthy and triggers other health management features.

Consider using worker process health detection for the following reasons:

• It allows IIS to determine whether each process has at least one thread available to work on requests, and then decide whether to pull new requests from HTTP.sys or to continue processing existing requests.

• It allows the worker process to request recycles when Internet Server Application Programming Interface (ISAPI) extensions such as ASP.NET and ASP are identified as unhealthy. The health detection feature uses the ability of a worker process to respond to a ping message. The worker process responds to a ping by requesting a recycle if one or more of the ISAPI extensions it has loaded is identified as unhealthy.