Question: how to upgrade domain controller from 2008 r2 to 2019?
Answer: It is not possible to do a direct, in-place upgrade of Windows Server 2008 R2 to Windows Server 2019. If you want to do an in-place upgrade, the process would require three steps: First step – Upgrade from Windows Server 2008 to 2012 or 2012 R2. Second step – Upgrade from Windows Server 2012 to Windows Server 2016.