Backend for allowing sample metrics to be toggled from ui

app/controllers/projects/environments_controller.rb

@@ -222,8 +222,8 @@ class Projects::EnvironmentsController < Projects::ApplicationController
 
   def metrics_dashboard_params
     params
-      .permit(:embedded, :group, :title, :y_label, :dashboard_path, :environment)
-      .merge(dashboard_path: params[:dashboard], environment: environment)
+      .permit(:embedded, :group, :title, :y_label, :dashboard_path, :environment, :sample_metrics)
+      .merge(dashboard_path: params[:dashboard], environment: environment, sample_metrics: params[:sample_metrics])
   end
 
   def include_all_dashboards?

config/routes/project.rb

@@ -242,7 +242,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
 
             get '/prometheus/api/v1/*proxy_path', to: 'environments/prometheus_api#proxy', as: :prometheus_api
 
-            get '/sample_metrics', to: 'environments/sample_metrics#query' if ENV['USE_SAMPLE_METRICS']
+            get '/sample_metrics', to: 'environments/sample_metrics#query'
           end
 
           collection do

lib/gitlab/metrics/dashboard/stages/endpoint_inserter.rb

@@ -16,7 +16,7 @@ module Gitlab
           private
 
           def endpoint_for_metric(metric)
-            if ENV['USE_SAMPLE_METRICS']
+            if params[:sample_metrics]
               Gitlab::Routing.url_helpers.sample_metrics_project_environment_path(
                 project,
                 params[:environment],

spec/lib/gitlab/metrics/dashboard/processor_spec.rb

@@ -86,6 +86,16 @@ describe Gitlab::Metrics::Dashboard::Processor do
           expect(metrics).to eq %w(metric_b metric_a2 metric_a1)
         end
       end
+
+      context 'when sample metrics are present' do
+        let(:process_params) { [project, dashboard_yml, sequence, { environment: environment, sample_metrics: true }] }
+
+        it 'includes a sample metrics path for the prometheus endpoint with each metric' do
+          expect(all_metrics).to satisfy_all do |metric|
+            metric[:prometheus_endpoint_path] == sample_metrics_path(metric[:id])
+          end
+        end
+      end
     end
 
     shared_examples_for 'errors with message' do |expected_message|
@@ -147,4 +157,12 @@ describe Gitlab::Metrics::Dashboard::Processor do
       query: query
     )
   end
+
+  def sample_metrics_path(metric)
+    Gitlab::Routing.url_helpers.sample_metrics_project_environment_path(
+      project,
+      environment,
+      identifier: metric
+    )
+  end
 end