Kofi

Recoverable from the machine versus only in your head. That is the whole filing rule.

The documentation half, and the distinction that makes it worth writing: what is recoverable from the machine. Why is not.

You can always read a config file and see what it says. What you cannot recover is that you set that odd variable because the default broke something else at three in the morning in March.

So write down the whys, and skip most of the whats:

Decisions with reasons. Why this service rather than the obvious alternative. Why this port. Why this filesystem.

Things that bit you. The workaround, and what it works around. These are the highest-value lines in any homelab document.

Dependencies between services. What must start before what, and what breaks if you stop this one.

External things. Which domain, which registrar, where DNS is hosted, which email address the certificates are registered to. This category is entirely absent from the machine and it is what stops a rebuild dead.

Where the data is and how it is backed up.

One file per service, a few lines each, alongside the config in the repository. And write it at the moment you do the thing, because a documentation session scheduled for later never happens and would be reconstructing from memory anyway: which is exactly the problem you have now.