salt: Add minion service module

nixos/modules/module-list.nix

@@ -130,6 +130,7 @@
   ./security/wrappers/default.nix
   ./security/sudo.nix
   ./services/admin/salt/master.nix
+  ./services/admin/salt/minion.nix
   ./services/amqp/activemq/default.nix
   ./services/amqp/rabbitmq.nix
   ./services/audio/alsa.nix

nixos/modules/services/admin/salt/minion.nix

@@ -0,0 +1,52 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+
+  cfg  = config.services.salt.minion;
+
+  fullConfig = lib.recursiveUpdate {
+    # Provide defaults for some directories to allow an immutable config dir
+    # NOTE: the config dir being immutable prevents `minion_id` caching
+
+    # Default is equivalent to /etc/salt/minion.d/*.conf
+    default_include = "/var/lib/salt/minion.d/*.conf";
+    # Default is in /etc/salt/pki/minion
+    pki_dir = "/var/lib/salt/pki/minion";
+  } cfg.configuration;
+  configDir = pkgs.writeTextDir "minion" (builtins.toJSON fullConfig);
+
+in
+
+{
+  options = {
+    services.salt.minion = {
+      enable = mkEnableOption "Salt minion service";
+      configuration = mkOption {
+        type = types.attrs;
+        default = {};
+        description = "Salt minion configuration as Nix attribute set.";
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = with pkgs; [ salt ];
+    systemd.services.salt-minion = {
+      description = "Salt Minion";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      path = with pkgs; [
+        utillinux
+      ];
+      serviceConfig = {
+        ExecStart = "${pkgs.salt}/bin/salt-minion --config-dir=${configDir}";
+        LimitNOFILE = 8192;
+        Type = "notify";
+        NotifyAccess = "all";
+      };
+    };
+  };
+}
+