Reinitialize samplers on restart

config/initializers/7_prometheus_metrics.rb

@@ -48,9 +48,9 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
 
   Gitlab::Cluster::LifecycleEvents.on_master_start do
     if defined?(::Unicorn)
-      Gitlab::Metrics::Samplers::UnicornSampler.initialize_instance(Settings.monitoring.unicorn_sampler_interval).start
+      Gitlab::Metrics::Samplers::UnicornSampler.reinitialize_instance(Settings.monitoring.unicorn_sampler_interval).start
     elsif defined?(::Puma)
-      Gitlab::Metrics::Samplers::PumaSampler.initialize_instance(Settings.monitoring.puma_sampler_interval).start
+      Gitlab::Metrics::Samplers::PumaSampler.reinitialize_instance(Settings.monitoring.puma_sampler_interval).start
     end
   end
 end

lib/gitlab/daemon.rb

@@ -10,6 +10,14 @@ module Gitlab
       @instance
     end
 
+    def self.reinitialize_instance(*args)
+      @instance.stop if @instance
+
+      @instance = new(*args)
+      Kernel.at_exit(&@instance.method(:stop))
+      @instance
+    end
+
     def self.instance
       @instance ||= initialize_instance
     end