nixos/prometheus: add unbound exporter

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

@@ -59,6 +59,7 @@ let
     "surfboard"
     "systemd"
     "tor"
+    "unbound"
     "unifi"
     "unifi-poller"
     "varnish"

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

@@ -0,0 +1,59 @@
+{ config, lib, pkgs, options }:
+
+with lib;
+
+let
+  cfg = config.services.prometheus.exporters.unbound;
+in
+{
+  port = 9167;
+  extraOpts = {
+    fetchType = mkOption {
+      # TODO: add shm when upstream implemented it
+      type = types.enum [ "tcp" "uds" ];
+      default = "uds";
+      description = ''
+        Which methods the exporter uses to get the information from unbound.
+      '';
+    };
+
+    telemetryPath = mkOption {
+      type = types.str;
+      default = "/metrics";
+      description = ''
+        Path under which to expose metrics.
+      '';
+    };
+
+    controlInterface = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      example = "/run/unbound/unbound.socket";
+      description = ''
+        Path to the unbound socket for uds mode or the control interface port for tcp mode.
+
+        Example:
+          uds-mode: /run/unbound/unbound.socket
+          tcp-mode: 127.0.0.1:8953
+      '';
+    };
+  };
+
+  serviceOpts = mkMerge ([{
+    serviceConfig = {
+      ExecStart = ''
+        ${pkgs.prometheus-unbound-exporter}/bin/unbound-telemetry \
+          ${cfg.fetchType} \
+          --bind ${cfg.listenAddress}:${toString cfg.port} \
+          --path ${cfg.telemetryPath} \
+          ${optionalString (cfg.controlInterface != null) "--control-interface ${cfg.controlInterface}"} \
+          ${toString cfg.extraFlags}
+      '';
+    };
+  }] ++ [
+    (mkIf config.services.unbound.enable {
+      after = [ "unbound.service" ];
+      requires = [ "unbound.service" ];
+    })
+  ]);
+}