When signing up for mastohost with an existing domain I own (whatever.com) the signup process forced me to use a subdomain (something.whatever.com). I don’t currently have a website on that root domain, but I would like to one day. Do I really have to have a long three part domain? Is there a way around it or is this a limitation of mastodon/mastohost?
It sounds like you’re saying you don’t currently have a website at “whatever.com,” but would like to at some point. That being the case, I’m not sure why you would not want put Mastodon on a subdomain (for example, on “mastodon.whatever.com,” rather than on “whatever.com”). If you don’t, you’re going to run into some fairly major problems when you have to move the Mastodon instance to a new URL.
Longer domains are less human readable. I don’t want to move the instance, I’d like it to always be at whatever.com
My email is emailhandle@whatever.com, I’d like my mastodon to be mastodonhandle@whatever.com
What I’m hearing is, this is possible but it’s more of an alias being setup on the whatever.com webserver but under the surface it’s always something.whatever.com?
The message you posted seems to indicate you can’t use “whatever.com” if there is another site already there, because of course you can’t… the same name can’t point two different places (well, it technically can, but don’t do that). I’m not super familiar with Mastodon, but this sounds like a warning rather than a restriction.
In any case, yes, you can make whatever.com a DNS alias for mastodon.whatever.com and handle it with configuration. Just be aware that if you ever want something else at whatever.com, it’s not easy to change the name later.
I don’t know about whether mastohost supports this or not, but Mastodon definitely allows you to host the service at e.g., mastodon.whatever.com but have your handle be mastodonhandle@whatever.com. This is documented here: https://docs.joinmastodon.org/admin/config/#web_domain