Simple proof of concept for how to do other types of services

nixos/modules/module-list.nix

···
   ./security/rtkit.nix
   ./security/wrappers/default.nix
   ./security/sudo.nix
+  ./service-managers/docker.nix
+  ./service-managers/trivial.nix
   ./services/admin/salt/master.nix
   ./services/admin/salt/minion.nix
   ./services/amqp/activemq/default.nix

nixos/modules/service-managers/docker.nix

···
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.docker-containers;
+
+  containerModule = {
+    script = mkOption {
+      type = types.lines;
+      description = "Shell commands executed as the service's main process.";
+    };
+  };
+
+  toContainer = name: value: pkgs.dockerTools.buildImage {
+    inherit name;
+    config = {
+      Cmd = [ value.script ];
+    };
+  };
+in {
+  options.docker-containers = mkOption {
+    default = {};
+    type = with types; attrsOf (types.submodule containerModule);
+    description = "Definition of docker containers";
+  };
+
+  config.system.build.toplevel-docker = lib.mapAttrs toContainer cfg;
+}

nixos/modules/service-managers/trivial.nix

···
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.trivial-services;
+
+  serviceModule.options = {
+    script = mkOption {
+      type = types.lines;
+      description = "Shell commands executed as the service's main process.";
+    };
+
+    environment = mkOption {
+      default = {};
+      type = types.attrs; # FIXME
+      example = { PATH = "/foo/bar/bin"; LANG = "nl_NL.UTF-8"; };
+      description = "Environment variables passed to the service's processes.";
+    };
+  };
+
+  launcher = name: value: pkgs.writeScript name ''
+    #!${pkgs.stdenv.shell} -eu
+
+    ${pkgs.writeScript "${name}-entry" value.script}
+  '';
+in {
+  options.trivial-services = mkOption {
+    default = {};
+    type = with types; attrsOf (types.submodule serviceModule);
+    description = "Definition of trivial services";
+  };
+
+  config.system.build.toplevel-trivial = lib.mapAttrs launcher cfg;
+}

nixos/modules/services/security/hologram-server.nix

···
     stats  = cfg.statsAddress;
     listen = cfg.listenAddress;
   });
+
+  script = "${pkgs.hologram.bin}/bin/hologram-server --debug --conf ${cfgFile}";
 in {
   options = {
     services.hologram-server = {
···
       after       = [ "network.target" ];
       wantedBy    = [ "multi-user.target" ];
 
-      serviceConfig = {
-        ExecStart = "${pkgs.hologram.bin}/bin/hologram-server --debug --conf ${cfgFile}";
-      };
+      inherit script;
+    };
+
+    docker-containers.hologram-server = {
+      inherit script;
+    };
+
+    trivial-services.hologram-server = {
+      inherit script;
     };
   };
 }