I have recently migrated a set of Windows Server 2008 R2 / IIS 7.5 servers to new servers running Windows Server 2012 / IIS 8.
I am experiencing some odd behavior from IIS. We have 2 identical servers, each server is running 2 web sites, each on their own app pool. The code for each of the web sites is identical. (Literally... same dll's and everything, just slightly different configuration).
The app pools are set to recycle on a schedule every 24 hours, but during that 24hr period, the CPU usage of the w3wp worker process jumps up in increments of 12.5% (the server has 8 processors, so I don't think that is a coincidence).
Once the CPU usage jumps up, it WILL NOT go back down until the app recycles. As far as I can tell, the app is doing nothing and processing NO requests at this time. I can block off all traffic to the server and the CPU usage will just stay there. I can even RESTART the web site, and the CPU usage stays the same. The only way to reset the CPU usage is to recycle or restart the app pool that it runs on.
I am somewhat certain that this issue has nothing to do with my code, but some sort of a poor IIS configuration or a change in IIS 8 that is working poorly with the hardware configuration or something?
Not sure if it's important or not, but these are Rackspace Performance Cloud servers.
Here is a screenshot to show you the CPU load over time on these servers (green arrows point to the times when the app pool recycles. You can see that each plateau is an integral multiple of 12.5%:
Has anyone observed this behavior? I have found this question from 2009 with someone having what appears to be the same issue with IIS 6:
Any help is much appreciated