multiple dns server setup

I recently asked about an issue with named.service not starting after an update from rhel 6 to 7. The setup I have is a server that I make changes to, that feeds the changes to 2 servers that perform dns. Two are used for redundancy, which is probably obvious.

I'd like to know more about how this works and is set up. I am not sure the terminology, otherwise I'd search for it. So, if anyone has a good source, especially for rhel 8, that would be great.

Thanks