From 88fb6d25d87f5ff6e75d471809bb61463e1c5cc6 Mon Sep 17 00:00:00 2001
From: Cole Helbling <cole.helbling@determinate.systems>
Date: Thu, 15 Jul 2021 10:37:54 -0700
Subject: [PATCH] nixos/prometheus-buildkite-agent-exporter: init

---
 .../from_md/release-notes/rl-2111.section.xml |  8 +++
 .../manual/release-notes/rl-2111.section.md   |  1 +
 .../monitoring/prometheus/exporters.nix       |  1 +
 .../prometheus/exporters/buildkite-agent.nix  | 64 +++++++++++++++++++
 4 files changed, 74 insertions(+)
 create mode 100644 nixos/modules/services/monitoring/prometheus/exporters/buildkite-agent.nix

diff --git a/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml b/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
index 88d075a9a482..fc1cec16ef90 100644
--- a/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
+++ b/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
@@ -99,6 +99,14 @@
           <link linkend="opt-services.hockeypuck.enable">services.hockeypuck</link>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <link xlink:href="https://github.com/buildkite/buildkite-agent-metrics">buildkite-agent-metrics</link>,
+          a command-line tool for collecting Buildkite agent metrics,
+          now has a Prometheus exporter available as
+          <link linkend="opt-services.prometheus.exporters.buildkite-agent.enable">services.prometheus.exporters.buildkite-agent</link>.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-21.11-incompatibilities">
diff --git a/nixos/doc/manual/release-notes/rl-2111.section.md b/nixos/doc/manual/release-notes/rl-2111.section.md
index f7275480ff81..9303393aba34 100644
--- a/nixos/doc/manual/release-notes/rl-2111.section.md
+++ b/nixos/doc/manual/release-notes/rl-2111.section.md
@@ -30,6 +30,7 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - [Hockeypuck](https://github.com/hockeypuck/hockeypuck), a OpenPGP Key Server. Available as [services.hockeypuck](#opt-services.hockeypuck.enable).
 
+- [buildkite-agent-metrics](https://github.com/buildkite/buildkite-agent-metrics), a command-line tool for collecting Buildkite agent metrics, now has a Prometheus exporter available as [services.prometheus.exporters.buildkite-agent](#opt-services.prometheus.exporters.buildkite-agent.enable).
 
 ## Backward Incompatibilities {#sec-release-21.11-incompatibilities}
 
diff --git a/nixos/modules/services/monitoring/prometheus/exporters.nix b/nixos/modules/services/monitoring/prometheus/exporters.nix
index 6bd075697fa2..d648de6a4148 100644
--- a/nixos/modules/services/monitoring/prometheus/exporters.nix
+++ b/nixos/modules/services/monitoring/prometheus/exporters.nix
@@ -27,6 +27,7 @@ let
     "bird"
     "bitcoin"
     "blackbox"
+    "buildkite-agent"
     "collectd"
     "dnsmasq"
     "domain"
diff --git a/nixos/modules/services/monitoring/prometheus/exporters/buildkite-agent.nix b/nixos/modules/services/monitoring/prometheus/exporters/buildkite-agent.nix
new file mode 100644
index 000000000000..7557480ac062
--- /dev/null
+++ b/nixos/modules/services/monitoring/prometheus/exporters/buildkite-agent.nix
@@ -0,0 +1,64 @@
+{ config, lib, pkgs, options }:
+
+with lib;
+
+let
+  cfg = config.services.prometheus.exporters.buildkite-agent;
+in
+{
+  port = 9876;
+  extraOpts = {
+    tokenPath = mkOption {
+      type = types.nullOr types.path;
+      apply = final: if final == null then null else toString final;
+      description = ''
+        The token from your Buildkite "Agents" page.
+
+        A run-time path to the token file, which is supposed to be provisioned
+        outside of Nix store.
+      '';
+    };
+    interval = mkOption {
+      type = types.str;
+      default = "30s";
+      example = "1min";
+      description = ''
+        How often to update metrics.
+      '';
+    };
+    endpoint = mkOption {
+      type = types.str;
+      default = "https://agent.buildkite.com/v3";
+      description = ''
+        The Buildkite Agent API endpoint.
+      '';
+    };
+    queues = mkOption {
+      type = with types; nullOr (listOf str);
+      default = null;
+      example = literalExample ''[ "my-queue1" "my-queue2" ]'';
+      description = ''
+        Which specific queues to process.
+      '';
+    };
+  };
+  serviceOpts = {
+    script =
+      let
+        queues = concatStringsSep " " (map (q: "-queue ${q}") cfg.queues);
+      in
+      ''
+        export BUILDKITE_AGENT_TOKEN="$(cat ${toString cfg.tokenPath})"
+        exec ${pkgs.buildkite-agent-metrics}/bin/buildkite-agent-metrics \
+          -backend prometheus \
+          -interval ${cfg.interval} \
+          -endpoint ${cfg.endpoint} \
+          ${optionalString (cfg.queues != null) queues} \
+          -prometheus-addr "${cfg.listenAddress}:${toString cfg.port}" ${concatStringsSep " " cfg.extraFlags}
+      '';
+    serviceConfig = {
+      DynamicUser = false;
+      RuntimeDirectory = "buildkite-agent-metrics";
+    };
+  };
+}