Move CleanupMultiprocDirService out of config.ru

changelogs/unreleased/300652-fix-prom-metrics-in-puma-single.yml

+---
+title: Move CleanupMultiprocDirService out of config.ru
+merge_request: 53139
+author:
+type: other

config.ru

@@ -22,12 +22,6 @@ def master_process?
 end
 
 warmup do |app|
-  # The following is necessary to ensure stale Prometheus metrics don't accumulate over time.
-  # It needs to be done as early as here to ensure metrics files aren't deleted.
-  # After we hit our app in `warmup`, first metrics and corresponding files already being created,
-  # for example in `lib/gitlab/metrics/requests_rack_middleware.rb`.
-  Prometheus::CleanupMultiprocDirService.new.execute if master_process?
-
   client = Rack::MockRequest.new(app)
   client.get('/')
 end

config/initializers/7_prometheus_metrics.rb

@@ -39,19 +39,24 @@ Sidekiq.configure_server do |config|
 end
 
 if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
-  Gitlab::Cluster::LifecycleEvents.on_worker_start do
-    defined?(::Prometheus::Client.reinitialize_on_pid_change) && Prometheus::Client.reinitialize_on_pid_change
+  # When running Puma in a Single mode, `on_master_start` and `on_worker_start` are the same.
+  # Thus, we order these events to run `reinitialize_on_pid_change` with `force: true` first.
+  Gitlab::Cluster::LifecycleEvents.on_master_start do
+    # Ensure that stale Prometheus metrics don't accumulate over time
+    Prometheus::CleanupMultiprocDirService.new.execute
 
-    Gitlab::Metrics::Samplers::RubySampler.initialize_instance.start
-    Gitlab::Metrics::Samplers::DatabaseSampler.initialize_instance.start
-    Gitlab::Metrics::Samplers::ThreadsSampler.initialize_instance.start
+    ::Prometheus::Client.reinitialize_on_pid_change(force: true)
 
-    if Gitlab::Runtime.action_cable?
-      Gitlab::Metrics::Samplers::ActionCableSampler.instance.start
+    if Gitlab::Runtime.unicorn?
+      Gitlab::Metrics::Samplers::UnicornSampler.instance(Settings.monitoring.unicorn_sampler_interval).start
+    elsif Gitlab::Runtime.puma?
+      Gitlab::Metrics::Samplers::PumaSampler.instance.start
     end
 
-    if Gitlab.ee? && Gitlab::Runtime.sidekiq?
-      Gitlab::Metrics::Samplers::GlobalSearchSampler.instance.start
+    Gitlab::Metrics.gauge(:deployments, 'GitLab Version', {}, :max).set({ version: Gitlab::VERSION }, 1)
+
+    unless Gitlab::Runtime.sidekiq?
+      Gitlab::Metrics::RequestsRackMiddleware.initialize_metrics
     end
 
     Gitlab::Ci::Parsers.instrument!
@@ -60,19 +65,19 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
     Gitlab::Metrics.error_detected!
   end
 
-  Gitlab::Cluster::LifecycleEvents.on_master_start do
-    ::Prometheus::Client.reinitialize_on_pid_change(force: true)
+  Gitlab::Cluster::LifecycleEvents.on_worker_start do
+    defined?(::Prometheus::Client.reinitialize_on_pid_change) && Prometheus::Client.reinitialize_on_pid_change
 
-    if Gitlab::Runtime.unicorn?
-      Gitlab::Metrics::Samplers::UnicornSampler.instance(Settings.monitoring.unicorn_sampler_interval).start
-    elsif Gitlab::Runtime.puma?
-      Gitlab::Metrics::Samplers::PumaSampler.instance.start
-    end
+    Gitlab::Metrics::Samplers::RubySampler.initialize_instance.start
+    Gitlab::Metrics::Samplers::DatabaseSampler.initialize_instance.start
+    Gitlab::Metrics::Samplers::ThreadsSampler.initialize_instance.start
 
-    Gitlab::Metrics.gauge(:deployments, 'GitLab Version', {}, :max).set({ version: Gitlab::VERSION }, 1)
+    if Gitlab::Runtime.action_cable?
+      Gitlab::Metrics::Samplers::ActionCableSampler.instance.start
+    end
 
-    unless Gitlab::Runtime.sidekiq?
-      Gitlab::Metrics::RequestsRackMiddleware.initialize_metrics
+    if Gitlab.ee? && Gitlab::Runtime.sidekiq?
+      Gitlab::Metrics::Samplers::GlobalSearchSampler.instance.start
     end
 
     Gitlab::Ci::Parsers.instrument!