Each service has it's own requirements so it's hard to make a generalised guide. Unless you're talking about fundamentals of running a linux vm that's exposed to the internet? There are guides on aspects of that, though I've yet to find anything really good in that area.
I mean how does discourse itself provide the discourse-hosted version (https://www.discourse.org/pricing)?
Do they spool up a new instance via K8S? Do they use terraform every time someone signs up? How do they manage one paid user wanting to run multiple discourses? There should be a guide for this, it would make a lot of OSS maintainers' lives much easier.
BIND, NGINX, Postfix, Apache... they all have excellent documentation on setup and securing.
I'm curious which aspect your seeing as poorly documented. Perhaps some specificity would help others point you at a reference.