nixos/prometheus-elasticsearch-exporter: init

Add a `services.prometheus.exporters.elasticsearch` module wrapping
`pkgs.prometheus-elasticsearch-exporter`, which also supports OpenSearch.

Credentials are kept out of the process arguments and the store via an
`environmentFile` carrying `ES_USERNAME`/`ES_PASSWORD` or `ES_API_KEY`,
which override any auth embedded in `--es.uri`. Collector toggles go
through the framework's `extraFlags`.

A NixOS test exercises the exporter against a single-node OpenSearch
instance.

Assisted-by: claude-code: claude-opus-4-8
(cherry picked from commit 7195e583ce)

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

@@ -62,6 +62,7 @@ let
         "domain"
         "dovecot"
         "ebpf"
+        "elasticsearch"
         "fail2ban"
         "fastly"
         "flow"

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

@@ -0,0 +1,62 @@
+{
+  config,
+  lib,
+  pkgs,
+  utils,
+  ...
+}:
+
+let
+  inherit (lib)
+    mkIf
+    mkOption
+    types
+    ;
+
+  inherit (utils) escapeSystemdExecArgs;
+
+  cfg = config.services.prometheus.exporters.elasticsearch;
+in
+{
+  port = 9114;
+  extraOpts = {
+    package = lib.mkPackageOption pkgs "prometheus-elasticsearch-exporter" { };
+
+    url = mkOption {
+      type = types.str;
+      default = "http://localhost:9200";
+      example = "https://localhost:9200";
+      description = ''
+        URI of the Elasticsearch (or OpenSearch) node to scrape, passed as
+        `--es.uri`. Any credentials embedded here are overridden by the
+        `ES_USERNAME`/`ES_PASSWORD` or `ES_API_KEY` environment variables when
+        {option}`environmentFile` is set.
+      '';
+    };
+
+    environmentFile = mkOption {
+      type = types.nullOr types.path;
+      default = null;
+      example = "/run/secrets/elasticsearch-exporter.env";
+      description = ''
+        Path to an environment file, as defined in {manpage}`systemd.exec(5)`,
+        used to pass credentials to the exporter without exposing them in the
+        process arguments. It should contain either `ES_USERNAME` and
+        `ES_PASSWORD`, or `ES_API_KEY`.
+      '';
+    };
+  };
+  serviceOpts = {
+    serviceConfig = {
+      EnvironmentFile = mkIf (cfg.environmentFile != null) cfg.environmentFile;
+      ExecStart = escapeSystemdExecArgs (
+        [
+          (lib.getExe cfg.package)
+          "--web.listen-address=${cfg.listenAddress}:${toString cfg.port}"
+          "--es.uri=${cfg.url}"
+        ]
+        ++ cfg.extraFlags
+      );
+    };
+  };
+}

nixos/tests/prometheus-exporters.nix

@@ -436,6 +436,30 @@ let
         '';
       };
 
+    elasticsearch =
+      { ... }:
+      {
+        exporterConfig = {
+          enable = true;
+          url = "http://localhost:9200";
+        };
+        metricProvider = {
+          # `services.elasticsearch` is unmaintained; OpenSearch is the same
+          # engine class and is explicitly supported by the exporter.
+          services.opensearch.enable = true;
+          virtualisation.memorySize = 2048;
+        };
+        exporterTest = ''
+          wait_for_unit("opensearch.service")
+          wait_for_open_port(9200)
+          wait_for_unit("prometheus-elasticsearch-exporter.service")
+          wait_for_open_port(9114)
+          succeed(
+              "curl -sSf localhost:9114/metrics | grep 'elasticsearch_cluster_health_status'"
+          )
+        '';
+      };
+
     fail2ban =
       { ... }:
       {

pkgs/by-name/pr/prometheus-elasticsearch-exporter/package.nix

@@ -2,6 +2,7 @@
   lib,
   buildGoModule,
   fetchFromGitHub,
+  nixosTests,
 }:
 buildGoModule (finalAttrs: {
   pname = "elasticsearch_exporter";
@@ -16,6 +17,8 @@ buildGoModule (finalAttrs: {
 
   vendorHash = "sha256-8y0M1b34eJpuHOuXPemhB5kKwBSgU7cMFxOaIZFS/bo=";
 
+  passthru.tests = { inherit (nixosTests.prometheus-exporters) elasticsearch; };
+
   meta = {
     description = "Elasticsearch stats exporter for Prometheus";
     mainProgram = "elasticsearch_exporter";