Nix

Getting a new machine requires a git pull, running nix rebuild / nix darwin rebuild and my machine is set up “exactly” the same as the other machine. Exact configuration, exact versions of software, completely deterministic.

No running custom GNU stow scripts that I used to do. No fragile non deterministic Ansible playbooks that randomly fail.

The caveat, Nix requires a time/investment from a user to learn (search hacker news post for nix). It’s language can be a bit unusual if not used ML style languages, it’s paradigm is a bit different to what you probably know, documentation is sparse although there’s more of it now and a good few blog posts teaching it.