Move initialization to master start

config/initializers/7_prometheus_metrics.rb

@@ -30,8 +30,6 @@ Gitlab::Application.configure do |config|
   config.middleware.insert(1, Gitlab::Metrics::RequestsRackMiddleware)
 end
 
-Gitlab::Metrics::RequestsRackMiddleware.initialize_http_request_duration_seconds
-
 Sidekiq.configure_server do |config|
   config.on(:startup) do
     # webserver metrics are cleaned up in config.ru: `warmup` block
@@ -56,5 +54,7 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
     elsif defined?(::Puma)
       Gitlab::Metrics::Samplers::PumaSampler.instance(Settings.monitoring.puma_sampler_interval).start
     end
+
+    Gitlab::Metrics::RequestsRackMiddleware.initialize_http_request_duration_seconds
   end
 end