Domains DNS Ideal hostname naming convention

I have an existing xenforo forum (www.forum.com) and planning to migrate it to a centos with cmm. I'm in the process of testing on build no. 1.

I know this is minor, but at 2am I'm stuck. I can see from the getting started guide there are concerns with naming convention for hostnames and DNS A records (i.e. can't use forum.com). The directions in section 1 talk about "Your default server hostname is usually the hostname used to purchase the VPS or dedicated server in the first place. It's basically a subdomain that links your order so would usually be something like hostname.newdomain.com where subdomain = hostname"...

but with digital ocean you just create new VMs and give a "name" on the outside, that eventually becomes the short and long hostname name inside.

So here is my confusion, in my initial test build, the hostname is 'main' and no version of main.forum.com appears inside via all the commands like: (uname -a, hostname, hostnamectl status --static, uname -f, uname -m, hostname -s, hostname -f).

But, I see it seems from the reading there is a preference to have some form of the long version (main.forum.com, or www.forum.com, or forum.com) appear in some of these hostname outputs, and have proper A records for them.

But my hangup is it doesn't seem consistent in the reading. This youtube video only has the short hostname version, but other helpful posts and guides show long form, but other helpful posts and guides show long form in some places.


What is the consensus for an ideal approach? For educational purposes, does it matter if I plan someday to insert cloudflare later? And does planning to add/park other domains later like 'blog.NEWsite.com' change it the ideal recommendation?

edit: I guess another way to ask this question... from the guide...

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If the hostname returned from uname -n command does not match the hostname you used to place your order for your server, then you can get your web host to correct it for you or do it yourself as follows:

And

Change HOSTNAME variable to your desired hostname. It has to be a valid hostname in format of hostname.newdomain.com

Why is long form necessary for uname -n output? (Digital Ocean simply places the outside label you originally pick as both short and long form inside).

 

If I go into production with only short form hostname, is there any gotchas with CMM to be aware?

By the way, what is your convention for each new domain you standup?

example:
website: www.centminmod.com (with A record)
hostname short form: main (with A record)
hostname long form: main.centminmod.com (with A record)