rkt: add service

nixos/modules/module-list.nix

@@ -507,6 +507,7 @@
   ./virtualisation/amazon-options.nix
   ./virtualisation/openvswitch.nix
   ./virtualisation/parallels-guest.nix
+  ./virtualisation/rkt.nix
   ./virtualisation/virtualbox-guest.nix
   ./virtualisation/virtualbox-host.nix
   ./virtualisation/vmware-guest.nix

nixos/modules/virtualisation/rkt.nix

@@ -0,0 +1,62 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.virtualisation.rkt;
+in
+{
+  options.virtualisation.rkt = {
+    enable = mkEnableOption "rkt metadata service";
+
+    gc = {
+      automatic = mkOption {
+        default = true;
+        type = types.bool;
+        description = "Automatically run the garbage collector at a specific time.";
+      };
+
+      dates = mkOption {
+        default = "03:15";
+        type = types.str;
+        description = ''
+          Specification (in the format described by
+          <citerefentry><refentrytitle>systemd.time</refentrytitle>
+          <manvolnum>5</manvolnum></citerefentry>) of the time at
+          which the garbage collector will run.
+        '';
+      };
+
+      options = mkOption {
+        default = "--grace-period=24h";
+        type = types.str;
+        description = ''
+          Options given to <filename>rkt gc</filename> when the
+          garbage collector is run automatically.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = [ pkgs.rkt ];
+
+    systemd.services.rkt = {
+      description = "rkt metadata service";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      serviceConfig = {
+        ExecStart = "${pkgs.rkt}/bin/rkt metadata-service";
+      };
+    };
+
+    systemd.services.rkt-gc = {
+      description = "rkt garbage collection";
+      startAt = optionalString cfg.gc.automatic cfg.gc.dates;
+      serviceConfig = {
+        Type = "oneshot";
+        ExecStart = "${pkgs.rkt}/bin/rkt gc ${cfg.gc.options}";
+      };
+    };
+  };
+}