In the past I’ve seen a lot of problems around virtual domain controllers. This varies from time synchronization problems to orphaned domain controllers (which were restored/ reverted from a snapshot). In a lot of cases the administrators of the virtual infrastructure does not understand what happened when a domain controller is restored from a snapshot.
Beside the problems I’ve seen I’ve also seen a lot of succesfull implementations of virtual Domain Controllers. These Domain Controllers were configured according a set of best practices. In the past we need to be aware that we cann’t snapshot a virtual Domain Controller and that we cann’t clone a virtual Domain Controller. This means that we apply traditional backup’s of these virtual machines (with an agent inside the virtual machine) and the we always install Domain Controllers from scratch instead of cloning an existing one.
Well this all belongs to the past with the comming new version of Windows Server: Windows Server 2012! With Windows Server 2012 we can build, deploy and protect domain controllers like every other virtual machine. Guess what: The Active Directory role in Windows Server 2012 is virtualization aware.