Use custom config

config/initializers/prometheus_exporter.rb

@@ -1,2 +1,24 @@
-require "govuk_app_config/govuk_prometheus_exporter"
-GovukPrometheusExporter.configure
+unless Rails.env.test? || Rails.env.development?
+  require "prometheus_exporter/middleware"
+  require "prometheus_exporter/instrumentation"
+
+  # This reports stats per request like HTTP status and timings
+  Rails.application.middleware.unshift PrometheusExporter::Middleware
+  # this reports basic process stats like RSS and GC info
+  PrometheusExporter::Instrumentation::Process.start(type: "master")
+
+  if defined?(Sidekiq)
+    Sidekiq.configure_server do |config|
+      config.server_middleware do |chain|
+        chain.add PrometheusExporter::Instrumentation::Sidekiq
+      end
+      config.death_handlers << PrometheusExporter::Instrumentation::Sidekiq.death_handler
+      config.on :startup do
+        PrometheusExporter::Instrumentation::Process.start(type: "sidekiq")
+        PrometheusExporter::Instrumentation::SidekiqProcess.start
+        PrometheusExporter::Instrumentation::SidekiqQueue.start
+        PrometheusExporter::Instrumentation::SidekiqStats.start
+      end
+    end
+  end
+end