2.10 Installing SQL Server Express on a Windows Domain Controller
Security Note We recommend against running SQL Server Express on a domain controller.
It is possible to install SQL Server Express on a Windows domain controller; however, it cannot run on a Windows Server 2003 domain controller as Local Service or Network Service. SQL Server service accounts should run as Windows domain user accounts. It is also possible to install SQL Server service accounts to run as Local System, but this option is not recommended.
Do not change the role of the server after you install SQL Server Express. For example, if you install SQL Server Express on a member server, do not use the Dcpromo tool to promote the server to a domain controller. Or, if you install SQL Server Express on a domain controller, do not use Dcpromo to demote the server to a member server. Changing the role of a server after you install SQL Server Express can result in loss of functionality and is not supported.