{ ... }:
{
  programs.ssh.knownHosts = {
    "build1.darmstadt.ccc.de".publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIE/oyJPRwW3bJoWKtXSrVOiqMaKq+9yd03+N2PuCbMKv";
    "build2.darmstadt.ccc.de".publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOZ7/eZLTfUD7Ejjio+8ivNFb8iyK1CD5Pq8uCDojT+z";
    "build3.darmstadt.ccc.de".publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIM2D/SwJf46XCoim06lOyO42JqJiTeM8UMkT4bYluJJr";
    "build4.darmstadt.ccc.de".publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDu9ZsbUYaCzzZv4vn22KrKi/R9pCfOEe4aYWyLd96C1";
  };

  nix = {
    distributedBuilds = true;
    buildMachines = [{
      hostName = "build1.darmstadt.ccc.de";
      protocol = "ssh";
      sshUser = "zebreus";
      sshKey = "/var/keys/id_remotebuild";
      systems = [
        "i686-linux"
        "x86_64-linux"
      ];
      maxJobs = 4;
      speedFactor = 6;
      supportedFeatures = [
        "big-parallel"
        "kvm"
        "nixos-test"
      ];
    }
      {
        hostName = "build2.darmstadt.ccc.de";
        protocol = "ssh";
        sshUser = "zebreus";
        sshKey = "/var/keys/id_remotebuild";
        systems = [
          "i686-linux"
          "x86_64-linux"
        ];
        maxJobs = 4;
        speedFactor = 6;
        supportedFeatures = [
          "big-parallel"
          "kvm"
          "nixos-test"
        ];
      }
      {
        hostName = "build3.darmstadt.ccc.de";
        protocol = "ssh";
        sshUser = "zebreus";
        sshKey = "/var/keys/id_remotebuild";
        systems = [
          "i686-linux"
          "x86_64-linux"
        ];
        maxJobs = 4;
        speedFactor = 6;
        supportedFeatures = [
          "big-parallel"
          "kvm"
          "nixos-test"
        ];
      }
      {
        hostName = "build4.darmstadt.ccc.de";
        protocol = "ssh";
        sshUser = "zebreus";
        sshKey = "/var/keys/id_remotebuild";
        systems = [
          "i686-linux"
          "x86_64-linux"
        ];
        # this node has half the cpu of the others
        maxJobs = 2;
        speedFactor = 6;
        supportedFeatures = [
          "big-parallel"
          "kvm"
          "nixos-test"
        ];
      }];
  };
}
