We currently have a AD domain with two replicating 2012 Server DCs. Domain Functional level is at 2012.
The Primary DC is a physical server with Windows Server 2012 Standard, and will be (7) years old.
The other replicating DC is a Windows Server 2012 DC that's a VM. The Hyper-V server that hosts this VM and another VM that is an Exchange 2010 Standard server is Windows Server 2012 Standard and is also close to (7) years old as well.
Overall, AD is healthy without issues. At the end of this year we will retire the existing Exchange 2010 server and move to O365 hosted mailboxes.
I am getting ready to purchase a Dell R440 that will serve as a Hyper-V server. Will purchase Windows Server 2019 Standard. I will install a new VM that will replace the primary 2012 DC that's on the physical server.
I also have an existing Dell R440 server that is a Hyper-V Server with Windows Server 2016 Standard. I have one VM that is a Windows Server 2016 that serves as a Storage server.
I plan on spinning up a second VM on the server to serve as a new replicating DC server.
When I purchase the new Dell R440 server along with Windows Server 2019 Standard, should I go ahead and install the Hyper-V Host with Windows Server 2019 Standard, and then also install the new primary DC that will hold all FSMO roles as a Windows Server 2019 Standard VM or downgrade it to Windows Server 2016 Standard?
I already have 25 Windows Server 2016 CALS. I can go ahead and bite the bullet and acquire the necessary 2019 CALS. The plan is to decommission the existing 2012 DCs with newly created DCs.
I just want to make sure if I have a 2019 DC operating with 2016 DC that I do not have issues. 2019 Server is still relatively new, and I do not want incur AD issues because of it. So that is why I am thinking of downgrading the os for the DC to 2016 server instead, but that might not be necessary.