Remote deployment with NixOS
Basic method
You can set up an agent on a remote NixOS machine by following the same NixOS instructions via an SSH connection.
Scriptable
Instead of deploying with Terraform, or NixOps with deployment.targetEnv = "none", you could script the deployment yourself.
nixos-rebuild has a --target-host option to make deployment via SSH easier. Evaluation of the NixOS configuration will happen on your local machine, but build and activation are performed via SSH.
[user@workstation:~/my-agent]$ NIXOS_CONFIG=$PWD/configuration.nix nixos-rebuild --target-host my-agentshell
Note that this determines the NixOS version via NIX_PATH, which defaults to a channel on workstation.
Updating the secret files is still a manual operation.