As someone with senior experience in cloud engineering here is my input, naming things is hard.
And God forbid you decide down the line you need a sub domain the terror of having service-b.service-a.com give me the chills.
But yeah 100% naming thing is difficult so you end up naming it after the software and using the group as the parent domain
Now this is how it should be !
I love the combination of preparation for both your own needs and that of others :3