But this is a solved problem since... well, at least since the beginning of internet. I managed 1000s of Linux & BSD systems over the past 25 years and I have scripts that do all that since the mid 90s that automate everything. I never install anything manual; if I have to do something new, I first write + test a script to do that remotely. Also, all this 'containerization' is not new; I have been using debootstrap/chroot since around that time as well. I run cleanly separated multiple versions of legacy (it is a bit scary how much time it takes to move something written early 2000s to a modern Linux version) + modern applications without any (hosting/reproducibility) issues since forever (in internet years anyway).

That's great but then you're not doing what the commenter above said and "logging in to a server and tinkering with it"

True; I learned many years ago that that is not a good plan. Although, I too, love it. But I use my X220 and Openpandora at home to satisfy that need. Those setups I could not reproduce if you paid me.

> The problem is when you need to duplicate that server or restore it due to some error, you have no idea what all the changes you made are.

A text file with some setup notes is enough for simple needs, or something like Ansible if its more complex. A lot of web apps aren't much more than some files, a database, and maybe a config file or three (all of which should be versioned and backed up).

I would be a lot more confident trying to back up my old school apps than the monstrosity we have on kubernetes we have at present.

Make backup of /etc and package list. Usually that's enough to quickly replicate a configuration. It's not like servers are crashing every day. I'm managing few servers for a last 5 years and I don't remember a single crash, they just work.