Hello Brent.
Good idea, because I also did not wanted to disturb Kal's post either since my question was answered.
And I'm also (as you could read) sometimes forgetting or overlooking things and am eager to learn things which might come in handy c.q. to why some things are done different on some places.
So I think I hear you saying when you create the server the admin user domain is eagle.ranbhosting.com and falcon.ranbhosting.com. Not just left blank.
There are domain names created like this by default when you install directadmin, so the hostnames are created as domain names by default.
The reason for this I don't remember exactly, but it has to do with the system needing some domain name do fill in basic domain information needed like for the mailserver and namservers etc.. A hostname is needed to configure exim, might be more reasons.
It's possible to delete that hostname domain created automatically, but in that case you best add the hostname to the DNS of the domain name.
But that is not what I meant, however it's quite possible that way, because when using subdomain as a domain name or in this case hostname as a domain name (technically also kind of a subdomain name), you can do things with it like creating SSL for the hostname and creating an rDNS/PTR record for the hostname.
However, I never used 1 domain name on more than 2 servers. I use a domain for every server.
In your example, your in fact working with subdomains (kind of), not domains.
So where would you host the domain name ranbhosting.com itself? because you would need for example
www.ranbhosting.com, it would not look professional to use
www.falcon.randbhosting.com. So on one of the two servers you need that randbhosting.com domain.
What I mean by using a domain as admin domain is like this.
Were using the same company, but now we only have 1 server. This has hostname eagle.randbhosting.com so domain is randbhosting.com which we use as admin domain. I enter "eagle" in dns to have that in there too. Than I can do anything from there. I have cron, ftp, email, dkim, spf, whatever I want, and the only thing I have to do is switch to userlevel.
Now we are getting a new server and wanting to transfer to there with the same hostname and nameservers (only other ip's). So I create an A record for falcon in dns of the randbhosting domain on server 1 and this way I can install and already reach the new server with the falcon hostname.
However, if all resellers and admins are created under admin, it can sometimes cause some isseus when moving servers, you can't move parts of them which sometimes is also necessary.
So nowadays we use some domain for example admindomain.com. The server gets server.admindomain.com. As admin, under userlevel we create the domain admindomain.com and can do anything we need to do as admin there, cron jobs, ftp, abuse mail, nameservers etc. etc. but we don't want to use this as main domain, so we do not create a website there. It's only for admin stuff.
I know cP is using this completely different, but cP is using root, not admin. And Plesk is doing it again different.
Now we create a second admin called rbadmin. This one gets the domain name randbhosting.com and because this will be the main domain, we also create the website here and if we also want nameservers with this name, we create nameservers with this name on the same ip's which are used for the default admin account.
Under this hosting account we can create resellers, we also can create more admins for other purposes. We had 5 servers, which were brought back to 2 servers, then 3 servers, 3 servers and a VPS and it was easy this way to move around admins and users, without having to move accounts to other admins first and hope nothing goes wrong.
But even if you want to servers like in your example, then on 1 server, you do need that randbdomain as admin domain if you want to create resellers falling under that domain, or if you don't, you at least need it to be a reseller account under the default admin, to be able to create user packages for your users.
So now this is what I'm wondering about. You're quite correct that both servers can't have randbhosting.com as domain name.
So that domain can only be used on 1 server. So to create resellers on the falcon server (which is server 2), you still need ad admin, don't need a domain to create resellers.
How do you do that with nameservers, use the multi-server setup? Because that's an option.
So it's very well possible to use a server with a domain name like you say. But in our case (or small hosting) I really don't see a problem to use the default admin account also for a domain name. In fact, that is working by design as you can also see from the personal license. It has always been like that in the past.
It can be used differently ofcourse, due to other needs, but if there are not other needs, in those cases I'm curious as to why people should not want to use the admin domain also for the main website and other stuff because it's that easy.
And it's not the root account which WHM uses, so yes that's different, and Plesk is doing it again different. So to me it just looks getting used to a bit unless peopl are doing this different like using the domain name for 2 servers, which I would never do myself, but that's a choice.
Sorry if the text is a bit long, but it explains various possibility's and also shows how we are using it at the moment, becasue we experienced a lot of server moves in the past. Now not anymore luckily.