A domain controller (DC) is a server that responds to security authentication requests within a Windows Server domain. A domain controller is the centerpiece of the Windows Active Directory service. It authenticates users, stores user account information and enforces security policy for a Windows domain. Best practices include setting up at least 2 redundant domain controllers and that nothing else – no software, no third-part applications, no roles – should be installed inside a domain controller. Virtualized domain controllers are supported.