This article shows how the app pools are monitored by the iis probe.
Why is the iis probe unable to discover app pools on Windows 2008 server?
The iis probe uses the perfmon probe to locate the counters from Performance Monitor (Perfmon). The counter used to find the application pools on a server is called APP_POOL_WAS. In order to check if the APP_POOL_WAS counter is installed on the system, please perform the following steps:
**Note: This counter is not added by default in Windows 2003 or Windows 2008 servers. This is what the counters will look like on these servers.
If the APP_POOL_WAS counter is not added to Performance Monitor by default, then the iis probe will not be able to monitor the application pools and will provide an error similar to the following in the iis.log:
The IIS probe has worked for 3 servers, but the 4th is not able to discover any of the 4 app pools on the server. The IIS probe log says:
"Dec 21 16:27:00:504  iis: sockServer: requested port 998 is already in use
Dec 21 16:27:00:504  iis: nimSession - failed to create server session on port 998, error code 22"
I tried using port 998, restarting the robot, and still unable to rediscover. I used port 999 by default on the 3 servers with success.