So what is this distribution? I decided to forgo my familiar RHEL/CentOS and set this up on Amazon Linux 2. It appears to be RHEL 7 at the core, but has some packages at later versions, and the concept of RHEL 8 appstream in the amazon-linux-extras command. Quite a combination.
Postfix, samba, and php version line up with RHEL 7. GCC is newer, but I can also install php version that still support by upstream without using a third party reposistory.