With nixops you also define define your configurations in nix (and can have interdependencies between them) then start machines or virtual machines as blank nix

With nixops you also define define your configurations in nix (and can have interdependencies between them) then start machines or virtual machines as blank nixos installs and add their ssh key and address for nixops to reconfigure and manage. I ultimately find it easier to have one host that is keeping track of all configurations and pushing my changes to all hosts since I otherwise end up with a lot of machines with different changes I've been working on.