auto configuration systems

[Xen]

I just want to ask here colloquially.

The promise of Linux is of course that you can modify your own system.

But if you do; you run into the issue of perpetuating your changes.

Keeping configuration alive through many installs is not very useful; 
and hence you seek a way to regenerate config or to reapply it from some 
config system that you design or use from someone else.

I am sure there are millions such systems in the world because everyone 
pretty much develops his own thing :p.

But are there any well known such systems that you use?

For example I had a set of patches that would turn off systemd 
cryptsetup because it doesn't support keyscripts; the installer script I 
created for it would just check everything and the end result would be a 
re-applying of all changes without destroying anything.

Because the script did all the checking, there was no headache for me. 
But this was a one time thing, and you look into formalizing the process 
so it doesn't take so much effort the next time. Then at some point you 
have a system in which you declaratively can specify patches or 
whatever, or changes, or commands, and you have a form of manifests and 
you just run a script that checks all the manifests and runs all the 
scripts and if you have this integrated very well it means that on a new 
system you can just "run all manifests" and presto you have the same 
system again.

One example is that in KDE (Kubuntu) there would be a problem with the 
KWallet not realizing that there was no KDE4 wallet to migrate; but 
still trying, and you required a manual config change to make it stop 
nagging and all of these things can be very tiring to have to apply by 
hand.

Other stuff may be installing a custom grub (if you have no package for 
it yet) or typical services (ie. in /etc/systemd/system) that you design 
for your system, or stuff in /etc/initramfs-tools/hooks, etc.

Many of these elements is stuff that stays with you over time. You can 
manually back up those files (or create a file list you can feed to tar 
and it will archive up all of these individual files or directories) or 
you can also just recreate the files or copy them from some config 
"unit" you have for regenerating system configs.

I have done at least in different situations:
- the tar list
- a single "redo config" script
- a manifest system (rudimentary)
- a script that can find and replace occurrances in an existing config.

And I know there are some that have developed these systems in-house and 
are using them company-wide, for instances. Lately it seems to be about 
yaml files? I don't know.

(I even at some point created a system that can automatically download 
reliable persistent links on the internet in terms of (mostly) open 
source sources or packages such that in the face of calamity or whatever 
you would be able to easily regenerate some (modified system) config 
including compiled binaries from the web all just for the sake of not 
having to repeat stuff manually in case calamity does strike (or you 
just want to move something to a different system). )

Making backups of "permanent files" is all nice and dandy but having 
regeneration "recipes" that can be automatically executed is like a much 
more condensed and meaningful collection of artifacts that does not get 
mingled with: default configuration options, pecularities of a current 
system, etc.

In addition perhaps to it being usable by others (or yourself).

And I was meaning to say this is all rather unfinished and incomplete 
and rudimentary.

So my question would have been: do you use any complete systems like 
that?