Add prometheus-nut-exporter module

nixos/modules/services/monitoring/prometheus/exporters.nix

@@ -51,6 +51,7 @@ let
     "nginx"
     "nginxlog"
     "node"
+    "nut"
     "openldap"
     "openvpn"
     "pihole"

nixos/modules/services/monitoring/prometheus/exporters/nut.nix

@@ -0,0 +1,50 @@
+{ config, lib, pkgs, options }:
+
+with lib;
+
+let
+  cfg = config.services.prometheus.exporters.nut;
+in
+{
+  port = 9199;
+  extraOpts = {
+    nutServer = mkOption {
+      type = types.str;
+      default = "127.0.0.1";
+      description = lib.mdDoc ''
+        Hostname or address of the NUT server
+      '';
+    };
+    nutUser = mkOption {
+      type = types.str;
+      default = "";
+      example = "nut";
+      description = lib.mdDoc ''
+        The user to log in into NUT server. If set, passwordPath should
+        also be set.
+
+        Default NUT configs usually permit reading variables without
+        authentication.
+      '';
+    };
+    passwordPath = mkOption {
+      type = types.nullOr types.path;
+      default = null;
+      apply = final: if final == null then null else toString final;
+      description = lib.mdDoc ''
+        A run-time path to the nutUser password file, which should be
+        provisioned outside of Nix store.
+      '';
+    };
+  };
+  serviceOpts = {
+    script = ''
+      ${optionalString (cfg.passwordPath != null)
+      "export NUT_EXPORTER_PASSWORD=$(cat ${toString cfg.passwordPath})"}
+      ${pkgs.prometheus-nut-exporter}/bin/nut_exporter \
+        --nut.server=${cfg.nutServer} \
+        --web.listen-address="${cfg.listenAddress}:${toString cfg.port}" \
+        ${optionalString (cfg.nutUser != "") "--nut.username=${cfg.nutUser}"}
+    '';
+  };
+}