Start local prometheus_exporter server only in puma/sidekiq startup (#35005)

config/initializers/prometheus_exporter.rb

@@ -5,16 +5,12 @@ if ENV['MASTODON_PROMETHEUS_EXPORTER_ENABLED'] == 'true'
   require 'prometheus_exporter/middleware'
 
   if ENV['MASTODON_PROMETHEUS_EXPORTER_LOCAL'] == 'true'
-    require 'prometheus_exporter/server'
-    require 'prometheus_exporter/client'
+    require 'mastodon/prometheus_exporter/local_server'
 
     # bind is the address, on which the webserver will listen
     # port is the port that will provide the /metrics route
-    server = PrometheusExporter::Server::WebServer.new bind: ENV.fetch('MASTODON_PROMETHEUS_EXPORTER_HOST', 'localhost'), port: ENV.fetch('MASTODON_PROMETHEUS_EXPORTER_PORT', '9394').to_i
-    server.start
-
-    # wire up a default local client
-    PrometheusExporter::Client.default = PrometheusExporter::LocalClient.new(collector: server.collector)
+    Mastodon::PrometheusExporter::LocalServer.bind = ENV.fetch('MASTODON_PROMETHEUS_EXPORTER_HOST', 'localhost')
+    Mastodon::PrometheusExporter::LocalServer.port = ENV.fetch('MASTODON_PROMETHEUS_EXPORTER_PORT', '9394').to_i
   end
 
   if ENV['MASTODON_PROMETHEUS_EXPORTER_WEB_DETAILED_METRICS'] == 'true'

config/initializers/sidekiq.rb

@@ -26,6 +26,12 @@ Sidekiq.configure_server do |config|
     require 'prometheus_exporter'
     require 'prometheus_exporter/instrumentation'
 
+    if ENV['MASTODON_PROMETHEUS_EXPORTER_LOCAL'] == 'true'
+      config.on :startup do
+        Mastodon::PrometheusExporter::LocalServer.setup!
+      end
+    end
+
     config.on :startup do
       # Ruby process metrics (memory, GC, etc)
       PrometheusExporter::Instrumentation::Process.start type: 'sidekiq'

config/puma.rb

@@ -21,6 +21,12 @@ if ENV['MASTODON_PROMETHEUS_EXPORTER_ENABLED'] == 'true'
   require 'prometheus_exporter'
   require 'prometheus_exporter/instrumentation'
 
+  if ENV['MASTODON_PROMETHEUS_EXPORTER_LOCAL'] == 'true'
+    before_fork do
+      Mastodon::PrometheusExporter::LocalServer.setup!
+    end
+  end
+
   on_worker_boot do
     # Ruby process metrics (memory, GC, etc)
     PrometheusExporter::Instrumentation::Process.start(type: 'puma')

lib/mastodon/prometheus_exporter/local_server.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require 'prometheus_exporter/server'
+require 'prometheus_exporter/client'
+
+module Mastodon::PrometheusExporter
+  module LocalServer
+    mattr_accessor :bind, :port
+
+    def self.setup!
+      server = PrometheusExporter::Server::WebServer.new(bind:, port:)
+      server.start
+
+      # wire up a default local client
+      PrometheusExporter::Client.default = PrometheusExporter::LocalClient.new(collector: server.collector)
+    end
+  end
+end