I've used Ansible and Salt and I've found them much easier than dealing with nix. With nix I always end up digging through the source code to figure out how to anything.

Previous to NixOS I was actually using a simple configuration management system I wrote myself in mawk. Basically a glorified templating dsl that would deploy itself by concatenating all my awk code and a base64 encoded tar.gz of config file templates then ssh itself to the server and bootstrap and run. I don't know what madness possessed me to do that but I would rather go back to that than nix right now.

When I go back to Debian I'm looking at maybe trying out https://propellor.branchable.com/

My Haskell isn't great but I would prefer learning a language I might actually use elsewhere.