Hello,
Thank you so much for posting here.
We recommend to add a new 2019 DC to the existing domain instead of upgrading the Windows Server 2008 R2 to Windows Server 2019. I suggest we check our AD health before we make any change in our AD environment.
1, Check DC health by running Dcdiag /v and check AD replication by running repadmin/showrepl and repadmin /replsum before joining the new DC.
2, The minimum requirement to add a Windows Server 2019 Domain Controller is a Windows Server 2008 functional level. The domain also has to use DFS-R as the engine to replicate SYSVOL. So before we add 2019 DC to the existing domain, we need to ensure the functional level is at least Windows Server 2008, and the SYSVOL folder replication type is DFSR.
In the actual application environment, it is recommended to deploy the certificate server independently, and it is not recommended to deploy CA server and the domain controller on the same server.
Besides, as mentioned we got only one DC in our environment. To avoid any problem, it is suggested to have at least two DCs in our environment. In case one DC could not work, the another could continue to work.
As for the first option, the new server will have the same IP address and hostname as the old server after the upgrade.
As for the second option, both servers will be Windows server 2019 after the upgrade.
Both options are OK, we could choose one according to our requirements.
For any question, please feel free to contact us.
Best regards,
Hannah Xiong
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