distributed build with nixbuild.net for nix-darwin

nixbuild.nix

let
  nixbuildDomain = "eu.nixbuild.net";
  nixbuildKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPIQCZc54poJ8vqawd8TraNryQeJnvH1eLpIDgbiqymM";
  nixbuildPlatforms = [ "x86_64-linux" "aarch64-linux" ];
  nixbuildFeatures = [ "big-parallel" "benchmark" "kvm" "nixos-test" ];
  nixbuildSSH = ''
    Host eu.nixbuild.net
      PubkeyAcceptedKeyTypes ssh-ed25519
      ServerAliveInterval 60
      IPQoS throughput
      IdentityFile /etc/ssh/ssh_host_ed25519_key
  '';
in
{
      nix = {
        distributedBuilds = true;
        buildMachines = forEach cfg.systems (system: {
          inherit system;
          hostName = nixbuildDomain;
          maxJobs = 100;
          supportedFeatures = nixbuildFeatures;
        });

        settings.extra-substituters = [ "ssh://eu.nixbuild.net" ];
        settings.trusted-public-keys = [ "nixbuild.net/CQ9XPX-1:8WFF5qINzG2FrrvIePqdH+XraKME30g3+Es3aCWBw24=" ];
      };
      
      programs.ssh.knownHosts.nixbuild = {
        hostNames = [ nixbuildDomain ];
        publicKey = nixbuildKey;
      };
      
      environment.etc."ssh/ssh_config.d/nixbuild".text = nixbuildSSH;
}