It's mostly bash scripts (I know I have stockholm syndrome there) and nixos-rebuild: https://www.haskellforall.com/2023/01/announcing-nixos-rebui...

All the nix deployment tools had too much magic and broke, but nixos-rebuild always works and it's part of Nix!

Disko was great for bootstrapping servers: https://github.com/nix-community/disko