{ ... }: {

  ####################################################################
  #
  #  NixOS's Configuration for Remote Building / Distributed Building
  #
  #  Related Docs:
  #    1. https://github.com/NixOS/nix/issues/7380
  #    2. https://nixos.wiki/wiki/Distributed_build
  ####################################################################

  # set local's max-job to 0 to force remote building(disable local building)
  # nix.settings.max-jobs = 0;
  nix.distributedBuilds = true;
  nix.buildMachines = 
    let
      sshUser = "ryan";
      # ssh key's path on local machine
      sshKey = "/home/ryan/.ssh/ai-idols";
      systems = [
        # native arch
        "x86_64-linux"

        # emulated arch using binfmt_misc and qemu-user
        "aarch64-linux"
        "riscv64-linux"
      ];
      # all available system features are poorly documentd here:
      #  https://github.com/NixOS/nix/blob/e503ead/src/libstore/globals.hh#L673-L687
      supportedFeatures = [
        "benchmark"
        "big-parallel"
        "kvm"
      ];
    in
      [
        {
          # some of my remote builders are running NixOS
          # and has the same sshUser, sshKey, systems, etc.
          inherit sshUser sshKey systems supportedFeatures;

          # the hostName should be:
          #   1. a hostname that can be resolved by DNS
          #   2. the ip address of the remote builder
          #   3. a host alias defined globally in /etc/ssh/ssh_config
          hostName = "aquamarine";
          # remote builder's max-job
          maxJobs = 4;
          # speedFactor's a signed integer
          # nix seems always try to build on the machine with the highest speedFactor
          speedFactor = 1;
        }
        {
          inherit sshUser sshKey systems supportedFeatures;
          hostName = "ruby";
          maxJobs = 2;
          speedFactor = 1;
        }
        {
          inherit sshUser sshKey systems supportedFeatures;
          hostName = "kana";
          maxJobs = 2;
          speedFactor = 1;
        }
      ];
  # optional, useful when the builder has a faster internet connection than yours
	nix.extraOptions = ''
		builders-use-substitutes = true
	'';

  # define the host alias for remote builders
  # this config will be written to /etc/ssh/ssh_config
  programs.ssh.extraConfig = ''
    Host ai
      HostName 192.168.5.100
      Port 22
    
    Host aquamarine
      HostName 192.168.5.101
      Port 22
    
    Host ruby
      HostName 192.168.5.102
      Port 22

    Host kana
      HostName 192.168.5.103
      Port 22
  '';

  # define the host key for remote builders so that nix can verify all the remote builders
  # this config will be written to /etc/ssh/ssh_known_hosts
  programs.ssh.knownHosts = {
    # 星野 愛久愛海, Hoshino Aquamarine
    aquamarine = {
      hostNames = [ "aquamarine" "192.168.5.101" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDnCQXlllHoLX5EvU+t6yP/npsmuxKt0skHVeJashizE";
    };

    # 星野 瑠美衣, Hoshino Rubii
    ruby = {
      hostNames = [ "ruby" "192.168.5.102" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICoIvsorGgnYpyunNrJfZ6Nyue7wBTx6LsyMOMrpgHJ/";
    };

    # 有馬 かな, Arima Kana
    kana = {
      hostNames = [ "kana" "192.168.5.103" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIEuoNB0OSjCFyS022e+ZQCIsb/nhkw/XcWjksqK3sh5x";
    };
  };
}