{ pkgs,lib, ... }:
{
  boot.kernel.sysctl."net.ipv4.ip_forward" = true;
  services.gitlab-runner = {
    enable = true;
    services= {
      # runner for building in docker via host's nix-daemon
      # nix store will be readable in runner, might be insecure
      nix = with lib;{
        # File should contain at least these two variables:
        # `CI_SERVER_URL`
        # `REGISTRATION_TOKEN`
        registrationConfigFile = toString <secrets/shackspace-gitlab-ci>;
        dockerImage = "alpine";
        dockerVolumes = [
          "/nix/store:/nix/store:ro"
          "/nix/var/nix/db:/nix/var/nix/db:ro"
          "/nix/var/nix/daemon-socket:/nix/var/nix/daemon-socket:ro"
        ];
        dockerDisableCache = true;
        # TODO: use the channel from <stockholm/krebs/nixpkgs.json>
        preBuildScript = pkgs.writeScript "setup-container" ''
          mkdir -p -m 0755 /nix/var/log/nix/drvs
          mkdir -p -m 0755 /nix/var/nix/gcroots
          mkdir -p -m 0755 /nix/var/nix/profiles
          mkdir -p -m 0755 /nix/var/nix/temproots
          mkdir -p -m 0755 /nix/var/nix/userpool
          mkdir -p -m 1777 /nix/var/nix/gcroots/per-user
          mkdir -p -m 1777 /nix/var/nix/profiles/per-user
          mkdir -p -m 0755 /nix/var/nix/profiles/per-user/root
          mkdir -p -m 0700 "$HOME/.nix-defexpr"
          . ${pkgs.nix}/etc/profile.d/nix.sh
          ${pkgs.nix}/bin/nix-channel --add https://nixos.org/channels/nixos-20.09 nixpkgs
          ${pkgs.nix}/bin/nix-channel --update nixpkgs
          ${pkgs.nix}/bin/nix-env -i ${concatStringsSep " " (with pkgs; [ nix cacert git openssh ])}
        '';
        environmentVariables = {
          ENV = "/etc/profile";
          USER = "root";
          NIX_REMOTE = "daemon";
          PATH = "/nix/var/nix/profiles/default/bin:/nix/var/nix/profiles/default/sbin:/bin:/sbin:/usr/bin:/usr/sbin";
          NIX_SSL_CERT_FILE = "/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt";
        };
        tagList = [ "nix" "shacklan" ];
      };
    };
  };
  systemd.services.gitlab-runner.restartIfChanged = false;
  systemd.services.docker.restartIfChanged = false;
}