deploy.sh

nixops deploy -I "nixpkgs=${PWD}/nixpkgs-armv6l.nix" -d somedeployment --include somesystem

nixpkgs-armv6l.nix

import <nixpkgs>
{
  localSystem = {
    system = "x86_64-linux";
  };
  crossSystem = {
    system = "armv6l-linux";
  };
}

output

error: a 'armv6l-linux' is required to build '/nix/store/sb4xngbfvhdr2g8gb3yd735c38lr98w0-perl-5.28.1.drv', but I am a 'x86_64-linux'
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

somedeployment.nix

{
  somesystem = 
  {
    nixpkgs.system = "armv6l-linux";
    # ...
  };
}