Docker entryscripts sometimes have significant magic baked in (alas), but quite often Docker is a distribution mechanism more than anything else. The Docker guides are - 9 times out of 10 - more than informative enough to show how to DIY in any other of the dozens if not hundreds of other system types you might have.
If you want to resist using the easy thing, I personally think it behooves you to not bounce so quick. You don't have to use it, and it's good nearly universal documentation as to how to operate the thing.