My first production use of kubernetes started out because we put in the entirety of what we had to migrate to new hosting into spreadsheet, with columns for various parts of stack used by the websites, and figured we would go insane trying to pack it up - or we would lose the contract because we would be as expensive as the last company.

Could we package it nicely without docker? Yes, but the effort to package it in docker was smaller than packaging it in a way where it wouldn't conflict on a single host, because the simple script becomes way harder when you need to handle multiple versions of the same package, something that most distro do not support at all (these days I think we could have done it with NixOS, but that's a different kettle of deranged fishes)

And then the complexity of managing the stack was quickly made easier by turning each site into separate artifact (docker container) handled by k8s manifests (especially when it came to dealing with about 1000 domains across those apps).

So, theoretically discipline is enough, practical world is much dirtier though.

Sounds quite explicable: Docker image created by Hungarian devs perhaps?

Docker is great for making sure that magic bash script that brings the system up actually works again on someone else’s computer or after a big upgrade on your dev machine or whatever.

So many custom build scripts I’ve run into over the years have some kind of unstated dependency on the initial system they were written on, or explicit dependencies on something tricky to install, and as such are really annoying to diagnose later on, especially if they make significant system changes.

Docker is strictly better than a folder full of bash scripts and a Readme.txt. I would have loved having it when I had to operate servers like that with tons of websites running on them. So much nicer to be able to manage dependency upgrades per-site rather than server-wide, invariably causing something to quietly break on one of 200 sites.

Second best are OpenSSL dependencies. I sincerely hope I won’t have to deal with that again.

The trick isn't installing things, it's uninstalling them. Docker container is isolated in ways your bash script equivalent is not - particularly when first developing it, when you're bound to make an occasional mistake.