nixos/prometheus-nats-exporter: new module

nixos/doc/manual/release-notes/rl-2405.section.md

@@ -163,6 +163,8 @@ The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been m
 
 - [Uni-Sync](https://github.com/EightB1ts/uni-sync), a synchronization tool for Lian Li Uni Controllers. Available as [hardware.uni-sync](#opt-hardware.uni-sync.enable)
 
+- [prometheus-nats-exporter](https://github.com/nats-io/prometheus-nats-exporter), a Prometheus exporter for NATS. Available as [services.prometheus.exporters.nats](#opt-services.prometheus.exporters.nats.enable).
+
 ## Backward Incompatibilities {#sec-release-24.05-incompatibilities}
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->

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

@@ -55,6 +55,7 @@ let
     "modemmanager"
     "mongodb"
     "mysqld"
+    "nats"
     "nextcloud"
     "nginx"
     "nginxlog"

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

@@ -0,0 +1,34 @@
+{ config, lib, pkgs, options, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.prometheus.exporters.nats;
+
+in
+{
+  port = 7777;
+
+  extraOpts = {
+    url = mkOption {
+      type = types.str;
+      default = "http://127.0.0.1:8222";
+      description = ''
+        NATS monitor endpoint to query.
+      '';
+    };
+  };
+
+  serviceOpts = {
+    serviceConfig = {
+      ExecStart = ''
+        ${pkgs.prometheus-nats-exporter}/bin/prometheus-nats-exporter \
+          -addr ${cfg.listenAddress} \
+          -port ${toString cfg.port} \
+          ${concatStringsSep " \\\n  " cfg.extraFlags} \
+          ${cfg.url}
+      '';
+    };
+  };
+}