Allegedly, on or about 15 January 2016, bruce sent:
I want to setup a few (4-5) different test servers. I want the servers to be able to communicate with each other via name. I'd also like to be able to access one of the servers by name, to allow me to ssh into the box via name, as opposed to ipaddress.
Everything I've seen suggests that I need a domainName, but I suspect that's due to most people wanting to setup webservers. If I'm setting up a box within DO's ip range, the box(es) shouldn't need an actual domain name should they?? I can understand that for a box to be accessed via/external to DO, it might need a domain name.
If the software isn't hardcoded to do a DNS lookup with a server, and will use the system to find out the IP for a name, then you can put your data into each computer's /etc/hosts file. Normally, your computers will consult the hosts file, then do a DNS lookup if the hosts file didn't have an answer. For a three computer system, this isn't too much hard work.
But if they won't consult the hosts file, then you'll need a DNS server. But most things won't require that much effort. Though it does become beneficial when you have quite a number of computers - you only have to configure one central point for all your LAN computer's name resolution.
Populate your hosts file in the usual way. With one line per associated addresses, and space-separated data (ip-address domainname alias-names).
e.g. 192.168.1.2 two.localdomain two
That gives you domain names for things that need a name with at least one dot in it, and short names for things that don't need it (and your own convenience).
If you don't want to go through registering a real domain name, then you need to pick one that will not be in use on the internet. It can cause them problems, it can cause you problems, if you use a pre-existing domain name. You might think you've picked a unique one, but may encounter problems browsing some website which has used it for some of their embedded content, and this will not be obvious to you.
Off the top of my head, I can think of three that shouldn't cause you problems. Using "localdomain", as Fedora already uses. Using "lan", as a gazillion other LANs use. Or making a subdomain of "example.com", which is specifically set up for use with examples.
e.g. lan.example.com.
Having said that, it is very useful to have your own domain name. You make experiments like this much easier on yourself. And you can give yourself a permanent email address that's not tied to your ISP (should you ever want to / need to leave it, you'd lose that address). While you might think your service provider may be around for ever, or may be a good service, experience had taught me otherwise, even the big ones.