Deploy NixOS configurations on other Machines

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NB this doesn’t work for different architectures nixos-rebuild fails cross-build a flake · Issue #166499 · NixOS/nixpkgs · GitHub.

Adapted from @misuzu’s answer, a workaround is:

$ sudo nix build /etc/nixos#nixosConfigurations.rasp-pi.config.system.build.toplevel --builders 'ssh-ng://rasp-pi aarch64-linux' --max-jobs 0 builders-use-substitutes --option builders-use-substitutes true
# relies on $(readlink ./result) already being in the rasp-pi's nix store from using it as a remote builder
# it would be nice if there was a way to avoid having to copy this back to the workstation machine
$ ssh root@rasp-pi nix-env -p /nix/var/nix/profiles/system --set $(readlink ./result)
$ ssh root@rasp-pi /nix/var/nix/profiles/system/bin/switch-to-configuration switch