prometheus module: add nodeExporter submodule

nixos/modules/module-list.nix

@@ -289,6 +289,7 @@
   ./services/monitoring/munin.nix
   ./services/monitoring/nagios.nix
   ./services/monitoring/prometheus/default.nix
+  ./services/monitoring/prometheus/node-exporter.nix
   ./services/monitoring/riemann.nix
   ./services/monitoring/riemann-dash.nix
   ./services/monitoring/riemann-tools.nix

nixos/modules/services/monitoring/prometheus/node-exporter.nix

@@ -0,0 +1,59 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.services.prometheus.nodeExporter;
+in {
+  options = {
+    services.prometheus.nodeExporter = {
+      enable = mkEnableOption "prometheus node exporter";
+
+      port = mkOption {
+        type = types.int;
+        default = 9100;
+        description = ''
+          Port to listen on.
+        '';
+      };
+
+      listenAddress = mkOption {
+        type = types.string;
+        default = "0.0.0.0";
+        description = ''
+          Address to listen on.
+        '';
+      };
+
+      enabledCollectors = mkOption {
+        type = types.listOf types.string;
+        default = [];
+        example = ''[ "systemd" ]'';
+        description = ''
+          Collectors to enable, additionally to the defaults.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    networking.firewall.allowedTCPPorts = [ cfg.port ];
+
+    systemd.services.prometheus-node-exporter = {
+      wantedBy = [ "multi-user.target" ];
+      after    = [ "network.target" ];
+      script = ''
+        ${pkgs.prometheus-node-exporter.bin}/bin/node_exporter \
+          ${optionalString (cfg.enabledCollectors != [])
+            ''-collectors.enabled ${concatStringsSep "," cfg.enabledCollectors}''} \
+          -web.listen-address ${cfg.listenAddress}:${toString cfg.port}
+      '';
+      serviceConfig = {
+        User = "nobody";
+        Restart  = "always";
+        PrivateTmp = true;
+        WorkingDirectory = /tmp;
+      };
+    };
+  };
+}