nixops vs rpi

gistfile1.txt

exarkun@baryon:~/Projects/PersonalInfrastructure$ cat physical.nix 
{ rpi =
  { config, pkgs, ... }:
  { deployment.targetHost = "nixos";
  };
}
exarkun@baryon:~/Projects/PersonalInfrastructure$ cat rpi.nix
{
  rpi =
  { pkgs, ... }:
  { # nixpkgs.system = "aarch64-linux";

    # RPi uses funky U-Boot dealie.  Tell NixOS we want that.
    boot.loader.generic-extlinux-compatible.enable = true;

    fileSystems."/".device = "/dev/disk/by-label/nixos";

    networking.wireless.enable = true;
  };
}
exarkun@baryon:~/Projects/PersonalInfrastructure$ nixops deploy --show-trace -d personal-infra --build-only --include rpi
trace: `lib.nixpkgsVersion` is deprecated, use `lib.version` instead!
building all machine configurations...
error: while evaluating the attribute 'buildCommand' of the derivation 'nixops-machines' at /nix/store/ps5g3m00amr7akphmdsn9pqzwz3rn3a1-nixpkgs-18.09.1228.a4c4cbb613c/nixpkgs/pkgs/stdenv/generic/make-derivation.nix:177:11:
while evaluating anonymous function at /nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/share/nix/nixops/eval-machine-info.nix:368:46, called from /nix/store/ps5g3m00amr7akphmdsn9pqzwz3rn3a1-nixpkgs-18.09.1228.a4c4cbb613c/nixpkgs/lib/attrsets.nix:200:54:
while evaluating the attribute 'config.system.build.toplevel' at /home/exarkun/.nix-defexpr/channels/nixpkgs/nixos/modules/system/activation/top-level.nix:273:5:
while evaluating 'foldr' at /home/exarkun/.nix-defexpr/channels/nixpkgs/lib/lists.nix:36:20, called from /home/exarkun/.nix-defexpr/channels/nixpkgs/nixos/modules/system/activation/top-level.nix:137:12:
while evaluating 'fold'' at /home/exarkun/.nix-defexpr/channels/nixpkgs/lib/lists.nix:39:15, called from /home/exarkun/.nix-defexpr/channels/nixpkgs/lib/lists.nix:43:8:
while evaluating 'showWarnings' at /home/exarkun/.nix-defexpr/channels/nixpkgs/nixos/modules/system/activation/top-level.nix:100:18, called from /home/exarkun/.nix-defexpr/channels/nixpkgs/nixos/modules/system/activation/top-level.nix:107:16:
while evaluating 'foldr' at /home/exarkun/.nix-defexpr/channels/nixpkgs/lib/lists.nix:36:20, called from /home/exarkun/.nix-defexpr/channels/nixpkgs/nixos/modules/system/activation/top-level.nix:100:23:
while evaluating 'fold'' at /home/exarkun/.nix-defexpr/channels/nixpkgs/lib/lists.nix:39:15, called from /home/exarkun/.nix-defexpr/channels/nixpkgs/lib/lists.nix:43:8:

Failed assertions:
- You must set the option ‘boot.loader.grub.devices’ or 'boot.loader.grub.mirroredBoots' to make the system bootable.
Traceback (most recent call last):
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/bin/..nixops-wrapped-wrapped", line 985, in <module>
    args.op()
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/bin/..nixops-wrapped-wrapped", line 407, in op_deploy
    max_concurrent_activate=args.max_concurrent_activate)
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/lib/python2.7/site-packages/nixops/deployment.py", line 1051, in deploy
    self.run_with_notify('deploy', lambda: self._deploy(**kwargs))
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/lib/python2.7/site-packages/nixops/deployment.py", line 1040, in run_with_notify
    f()
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/lib/python2.7/site-packages/nixops/deployment.py", line 1051, in <lambda>
    self.run_with_notify('deploy', lambda: self._deploy(**kwargs))
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/lib/python2.7/site-packages/nixops/deployment.py", line 991, in _deploy
    self.configs_path = self.build_configs(dry_run=dry_run, repair=repair, include=include, exclude=exclude)
  File "/nix/store/v0p6praaqb5j6wydv710c2vixzls27c9-nixops-1.6/lib/python2.7/site-packages/nixops/deployment.py", line 659, in build_configs
    raise Exception("unable to build all machine configurations")
Exception: unable to build all machine configurations
exarkun@baryon:~/Projects/PersonalInfrastructure$