NixOS is the system configuration layer and closer to puppet in solo mode. With a single (or multiple) nix file(s) it's possible to configure a machine and it's

NixOS is the system configuration layer and closer to puppet in solo mode. With a single (or multiple) nix file(s) it's possible to configure a machine and it's services entirely. NixOps is the cloud configuration layer, it provisions cloud resources and uploads NixOS configuration to the machines. It's closer to terraform in that regard. It also has a state file (currently sqlite3) and uses a push model to propagate configuration changes. What's missing right now is a third option where an agent is installed on the machines for a more dynamic configuration of the cluster as a whole. This role will probably be filled by Kubernetes or Nomad.