Hello @Josiah brainard ,
Thank you for posting here.
Please confirm the following information at your convenience:
1.How many Domains do you have in your AD domain?
2.How many DCs in each domain if you have multiple domains?
3.What are the operating system of all DCs?
4.Are all DCs in your domain also DNS servers?
As I understand:
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.
5.What is the forest/domain functional level? Should be at least Windows Server 2008 functional level.
6.What is the SYSVOL replication engine? FRS or DFSR? Should be DFSR.
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DFSR\Parameters\SysVols\Migrating Sysvols\LocalState registry subkey. If this registry subkey exists and its value is set to 3 (ELIMINATED), DFSR is being used. If the subkey does not exist, or if it has a different value, FRS is being used.
For your request, you want to add a server 2019 to the existing domain, we can set one IP address of active DC/DNS server as its Preferred DNS.
Then try to join this server 2019 to domain and provide one domain credential.
After adding the server 2019 to domain, then check the information before we promoting server 2019 as DC.
Before we do any change in existing AD domain environment, we had better do:
1.Check if AD environment is healthy. Check all DCs in this domain is working fine by running Dcdiag /v. Check if AD replication works properly by running repadmin /showrepl and repadmin /replsum.
forest/domain functional level should be at least Windows Server 2008 functional level
2.SYSVOL replication should be DFSR.
3.Back up all domain controllers.
4.Check both SYSVOL folder and Netlogon folder are shared by running net share on each DC.
5.Check we can update gpupdate /force on each DC successfully.
Based on the description "after it reboots and i try to promote it to a DC it says it cannot contact to domain controller", which DC do you specify when you select replication partner?
Hope the information above is helpful.
Should you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou