Drop prometheus_initializer_refactor FF

This was enabled by default.

config/feature_flags/development/prometheus_initializer_refactor.yml

----
-name: prometheus_initializer_refactor
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/81133
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/353446
-milestone: '14.9'
-type: development
-group: group::memory
-default_enabled: true

config/initializers/7_prometheus_metrics.rb

 # frozen_string_literal: true
 
-return if Feature.feature_flags_available? && Feature.enabled?(:prometheus_initializer_refactor, default_enabled: :yaml)
-
 # Keep separate directories for separate processes
 def prometheus_default_multiproc_dir
   return unless Rails.env.development? || Rails.env.test?
@@ -18,8 +16,6 @@ end
 ::Prometheus::Client.configure do |config|
   config.logger = Gitlab::AppLogger
 
-  config.initial_mmap_file_size = 4 * 1024
-
   config.multiprocess_files_dir = ENV['prometheus_multiproc_dir'] || prometheus_default_multiproc_dir
 
   config.pid_provider = ::Prometheus::PidProvider.method(:worker_id)
@@ -30,6 +26,10 @@ Gitlab::Application.configure do |config|
   config.middleware.insert_after(Labkit::Middleware::Rack, Gitlab::Metrics::RequestsRackMiddleware)
 end
 
+# Any actions beyond this check should only execute outside of tests, when running in an application
+# context (i.e. not in the Rails console or rspec) and when users have enabled metrics.
+return if Rails.env.test? || !Gitlab::Runtime.application? || !Gitlab::Metrics.prometheus_metrics_enabled?
+
 if Gitlab::Runtime.sidekiq? && (!ENV['SIDEKIQ_WORKER_ID'] || ENV['SIDEKIQ_WORKER_ID'] == '0')
   # The single worker outside of a sidekiq-cluster, or the first worker (sidekiq_0)
   # in a cluster of processes, is responsible for serving health checks.
@@ -48,29 +48,29 @@ if Gitlab::Runtime.sidekiq? && (!ENV['SIDEKIQ_WORKER_ID'] || ENV['SIDEKIQ_WORKER
   end
 end
 
-if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
+Gitlab::Cluster::LifecycleEvents.on_master_start do
   # 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
   ::Prometheus::Client.reinitialize_on_pid_change(force: true)
 
-    if Gitlab::Runtime.puma?
-      Gitlab::Metrics::Samplers::PumaSampler.instance.start
-    end
-
   Gitlab::Metrics.gauge(:deployments, 'GitLab Version', {}, :max).set({ version: Gitlab::VERSION, revision: Gitlab.revision }, 1)
 
   if Gitlab::Runtime.puma?
     Gitlab::Metrics::RequestsRackMiddleware.initialize_metrics
+
+    Gitlab::Metrics::Samplers::PumaSampler.instance.start
+
+    # Starts a metrics server to export metrics from the Puma primary.
+    Gitlab::Metrics::Exporter::WebExporter.instance.start
   end
 
   Gitlab::Ci::Parsers.instrument!
-  rescue IOError => e
+rescue IOError => e
   Gitlab::ErrorTracking.track_exception(e)
   Gitlab::Metrics.error_detected!
-  end
+end
 
-  Gitlab::Cluster::LifecycleEvents.on_worker_start do
+Gitlab::Cluster::LifecycleEvents.on_worker_start do
   defined?(::Prometheus::Client.reinitialize_on_pid_change) && ::Prometheus::Client.reinitialize_on_pid_change
   logger = Gitlab::AppLogger
   Gitlab::Metrics::Samplers::RubySampler.initialize_instance(logger: logger).start
@@ -78,6 +78,12 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
   Gitlab::Metrics::Samplers::ThreadsSampler.initialize_instance(logger: logger).start
 
   if Gitlab::Runtime.puma?
+    # Since we are running a metrics server on the Puma primary, we would inherit
+    # this thread after forking into workers, so we need to explicitly stop it here.
+    # NOTE: This will not be necessary anymore after moving to an external server
+    # process via https://gitlab.com/gitlab-org/gitlab/-/issues/350548
+    Gitlab::Metrics::Exporter::WebExporter.instance.stop
+
     Gitlab::Metrics::Samplers::ActionCableSampler.instance(logger: logger).start
   end
 
@@ -86,17 +92,12 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
   end
 
   Gitlab::Ci::Parsers.instrument!
-  rescue IOError => e
+rescue IOError => e
   Gitlab::ErrorTracking.track_exception(e)
   Gitlab::Metrics.error_detected!
-  end
 end
 
 if Gitlab::Runtime.puma?
-  Gitlab::Cluster::LifecycleEvents.on_master_start do
-    Gitlab::Metrics::Exporter::WebExporter.instance.start
-  end
-
   Gitlab::Cluster::LifecycleEvents.on_before_graceful_shutdown do
     # We need to ensure that before we re-exec or shutdown server
     # we do stop the exporter
@@ -111,12 +112,4 @@ if Gitlab::Runtime.puma?
     # but it should not be needed
     Gitlab::Metrics::Exporter::WebExporter.instance.stop
   end
-
-  Gitlab::Cluster::LifecycleEvents.on_worker_start do
-    # The `#close_on_exec=` takes effect only on `execve`
-    # but this does not happen for Ruby fork
-    #
-    # This does stop server, as it is running on master.
-    Gitlab::Metrics::Exporter::WebExporter.instance.stop
-  end
 end

config/initializers/7_prometheus_metrics_new.rb

-# frozen_string_literal: true
-
-return unless Feature.feature_flags_available? && Feature.enabled?(:prometheus_initializer_refactor, default_enabled: :yaml)
-
-# Keep separate directories for separate processes
-def prometheus_default_multiproc_dir
-  return unless Rails.env.development? || Rails.env.test?
-
-  if Gitlab::Runtime.sidekiq?
-    Rails.root.join('tmp/prometheus_multiproc_dir/sidekiq')
-  elsif Gitlab::Runtime.puma?
-    Rails.root.join('tmp/prometheus_multiproc_dir/puma')
-  else
-    Rails.root.join('tmp/prometheus_multiproc_dir')
-  end
-end
-
-::Prometheus::Client.configure do |config|
-  config.logger = Gitlab::AppLogger
-
-  config.multiprocess_files_dir = ENV['prometheus_multiproc_dir'] || prometheus_default_multiproc_dir
-
-  config.pid_provider = ::Prometheus::PidProvider.method(:worker_id)
-end
-
-Gitlab::Application.configure do |config|
-  # 0 should be Sentry to catch errors in this middleware
-  config.middleware.insert_after(Labkit::Middleware::Rack, Gitlab::Metrics::RequestsRackMiddleware)
-end
-
-# Any actions beyond this check should only execute outside of tests, when running in an application
-# context (i.e. not in the Rails console or rspec) and when users have enabled metrics.
-return if Rails.env.test? || !Gitlab::Runtime.application? || !Gitlab::Metrics.prometheus_metrics_enabled?
-
-if Gitlab::Runtime.sidekiq? && (!ENV['SIDEKIQ_WORKER_ID'] || ENV['SIDEKIQ_WORKER_ID'] == '0')
-  # The single worker outside of a sidekiq-cluster, or the first worker (sidekiq_0)
-  # in a cluster of processes, is responsible for serving health checks.
-  #
-  # Do not clean the metrics directory here - the supervisor script should
-  # have already taken care of that.
-  Sidekiq.configure_server do |config|
-    config.on(:startup) do
-      # In https://gitlab.com/gitlab-org/gitlab/-/issues/345804 we are looking to
-      # only serve health-checks from a worker process; for backwards compatibility
-      # we still go through the metrics exporter server, but start to configure it
-      # with the new settings keys.
-      exporter_settings = Settings.monitoring.sidekiq_health_checks
-      Gitlab::Metrics::Exporter::SidekiqExporter.instance(exporter_settings).start
-    end
-  end
-end
-
-Gitlab::Cluster::LifecycleEvents.on_master_start do
-  # 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.
-  ::Prometheus::Client.reinitialize_on_pid_change(force: true)
-
-  Gitlab::Metrics.gauge(:deployments, 'GitLab Version', {}, :max).set({ version: Gitlab::VERSION, revision: Gitlab.revision }, 1)
-
-  if Gitlab::Runtime.puma?
-    Gitlab::Metrics::RequestsRackMiddleware.initialize_metrics
-
-    Gitlab::Metrics::Samplers::PumaSampler.instance.start
-
-    # Starts a metrics server to export metrics from the Puma primary.
-    Gitlab::Metrics::Exporter::WebExporter.instance.start
-  end
-
-  Gitlab::Ci::Parsers.instrument!
-rescue IOError => e
-  Gitlab::ErrorTracking.track_exception(e)
-  Gitlab::Metrics.error_detected!
-end
-
-Gitlab::Cluster::LifecycleEvents.on_worker_start do
-  defined?(::Prometheus::Client.reinitialize_on_pid_change) && ::Prometheus::Client.reinitialize_on_pid_change
-  logger = Gitlab::AppLogger
-  Gitlab::Metrics::Samplers::RubySampler.initialize_instance(logger: logger).start
-  Gitlab::Metrics::Samplers::DatabaseSampler.initialize_instance(logger: logger).start
-  Gitlab::Metrics::Samplers::ThreadsSampler.initialize_instance(logger: logger).start
-
-  if Gitlab::Runtime.puma?
-    # Since we are running a metrics server on the Puma primary, we would inherit
-    # this thread after forking into workers, so we need to explicitly stop it here.
-    # NOTE: This will not be necessary anymore after moving to an external server
-    # process via https://gitlab.com/gitlab-org/gitlab/-/issues/350548
-    Gitlab::Metrics::Exporter::WebExporter.instance.stop
-
-    Gitlab::Metrics::Samplers::ActionCableSampler.instance(logger: logger).start
-  end
-
-  if Gitlab.ee? && Gitlab::Runtime.sidekiq?
-    Gitlab::Metrics::Samplers::GlobalSearchSampler.instance(logger: logger).start
-  end
-
-  Gitlab::Ci::Parsers.instrument!
-rescue IOError => e
-  Gitlab::ErrorTracking.track_exception(e)
-  Gitlab::Metrics.error_detected!
-end
-
-if Gitlab::Runtime.puma?
-  Gitlab::Cluster::LifecycleEvents.on_before_graceful_shutdown do
-    # We need to ensure that before we re-exec or shutdown server
-    # we do stop the exporter
-    Gitlab::Metrics::Exporter::WebExporter.instance.stop
-  end
-
-  Gitlab::Cluster::LifecycleEvents.on_before_master_restart do
-    # We need to ensure that before we re-exec server
-    # we do stop the exporter
-    #
-    # We do it again, for being extra safe,
-    # but it should not be needed
-    Gitlab::Metrics::Exporter::WebExporter.instance.stop
-  end
-end