On our Domain Controller (Windows Server 2008), we have a Domain Group Policy setting for scheduling of Windows Updates.
Screenshot is attached showing:
1) Option 4 - Auto Download and schedule the installation
2) Scheduled Install Day - Every Sunday
3) Scheduled Install Time - 02:00
We're using these settings primarily to have our servers install updates and reboot during off-peak hours. In our environment, we have physical boxes running Windows Server 2012 (Host OS) and VM's on these physical boxes running (Guest OS) Windows Server 2012. All servers (physical boxes and VM's) are members of our domain.
Our primary problem resides with the physical boxes. It seems that the download of Windows updates (if available) is occurring nightly on these servers. Given the settings above, we'd expect those updates to be installed "Every Sunday" at "2:00 a.m.". This schedule seems to be working. We'd also expect those servers to reboot after those updates are installed; again, during off-peak hours. However, this is not happening.
We're seeing an automatic reboot of these physical boxes occur at random during the following days after the updates are installed. Our end users are accessing software installed on the VM's which are, of course, running on the physical boxes. When the random reboot of the physical box occurs (more often than not during the work day), our end users are left with no connectivity for as long as it takes the server to reboot. The VM's, as expected, seem to go in to a "Paused" state while the reboot of the physical box occurs.
Once the physical box reboots, the end users are able to connect to software running on the VM's. It sometimes takes 20-30 minutes for this process to finish.
There seems to be an update that resolves this issue for Windows Server 2012. A screenshot, "Hotfix", is also attached.