prometheus module: add varnishExporter

nixos/modules/module-list.nix

@@ -308,9 +308,11 @@
   ./services/monitoring/munin.nix
   ./services/monitoring/nagios.nix
   ./services/monitoring/prometheus/default.nix
+  ./services/monitoring/prometheus/alertmanager.nix
   ./services/monitoring/prometheus/nginx-exporter.nix
   ./services/monitoring/prometheus/node-exporter.nix
-  ./services/monitoring/prometheus/alertmanager.nix
+  ./services/monitoring/prometheus/snmp-exporter.nix
+  ./services/monitoring/prometheus/varnish-exporter.nix
   ./services/monitoring/riemann.nix
   ./services/monitoring/riemann-dash.nix
   ./services/monitoring/riemann-tools.nix

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

@@ -0,0 +1,51 @@
+{ config, pkgs, lib, ... }:
+
+# Shamelessly cribbed from nginx-exporter.nix. ~ C.
+with lib;
+
+let
+  cfg = config.services.prometheus.varnishExporter;
+in {
+  options = {
+    services.prometheus.varnishExporter = {
+      enable = mkEnableOption "prometheus Varnish exporter";
+
+      port = mkOption {
+        type = types.int;
+        default = 9131;
+        description = ''
+          Port to listen on.
+        '';
+      };
+
+      extraFlags = mkOption {
+        type = types.listOf types.str;
+        default = [];
+        description = ''
+          Extra commandline options when launching the Varnish exporter.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.prometheus-varnish-exporter = {
+      description = "Prometheus exporter for Varnish metrics";
+      unitConfig.Documentation = "https://github.com/jonnenauha/prometheus_varnish_exporter";
+      wantedBy = [ "multi-user.target" ];
+      path = [ pkgs.varnish ];
+      script = ''
+        exec ${pkgs.prometheus-varnish-exporter}/bin/prometheus_varnish_exporter \
+          -web.listen-address :${toString cfg.port} \
+          ${concatStringsSep " \\\n  " cfg.extraFlags}
+      '';
+      serviceConfig = {
+        User = "nobody";
+        Restart = "always";
+        PrivateTmp = true;
+        WorkingDirectory = /tmp;
+        ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
+      };
+    };
+  };
+}