How to access multiple computers via RDP using a domain name?

Question

Domain Name System

The crux of the matter is this. There is virtualization on Ovirt. One of the virtual machines has Windows Server deployed with the domain ad.example.com , DNS and DHCP. Example.com was purchased from a domain registrar, which in turn leads to the white address 123.123.123.123 . Next, the RDP port was forwarded through the router to the address at 192.168.100.100 on the local network (address of the AD server). This was done for fun and temporarily, and I assume that this should not be done. But in fact, now I can run the "Remote Desktop" program on any computer with Internet access, enter example.com and go to the remote computer.
On the Internet, I saw such an implementation - *.example.com , where *- computer name from my local network. That is, for example: vm-1.example.com , vm-2.example.com and so on. Just enter your username and password from your machine and work.
But the question is how to implement this, if the registrar of my domain, in fact, has a subdomain and my static ip to which it leads in the settings. Of course, if all virtual machines had white addresses, then there would be no problems, but what to do when there is only one static address? Maybe the server itself can somehow redirect them?
Of course, it immediately comes to mind to do port forwarding - you enter on any computer example.com : 777well, the router redirects you to the desired computer. But with subdomains it looks somehow more concise or something)). And the question of course with security - is it normal or not? Maybe I'm missing some technology for such access.

Answer 1

I deployed VPN Ikev2 at the border and I get IP addresses issued by vpn clients from dhcp on the server, and then by the name of the computer inside the network I can easily connect to any machine (to which, of course, you can connect according to a number of rules). And on the router, I just wrote the logic which ports from the white address are routed to ports on the server

Answer 2

It's probably worth taking a closer look at the "Remote Desktop Gateway" technology.
RDC does not look at the Internet and you can connect through one gateway to several different servers on the local network ..
Well, separate 2nd-level domains are not needed