Merge branch 'pawel/show_empty_page_when_prometheus_metrics_are_disabled-35639' into 'master'

Make Prometheus metrics endpoint return empty response when metrics are disabled

Closes #35639

See merge request gitlab-org/gitlab-ce!14490

3 files changed, 16 insertions, 8 deletions

diff --git a/app/controllers/metrics_controller.rb b/app/controllers/metrics_controller.rb
index 37587a52eaf..d81ad135198 100644
--- a/app/controllers/metrics_controller.rb
+++ b/app/controllers/metrics_controller.rb
@@ -3,10 +3,16 @@ class MetricsController < ActionController::Base
 
   protect_from_forgery with: :exception
 
-  before_action :validate_prometheus_metrics
-
   def index
-    render text: metrics_service.metrics_text, content_type: 'text/plain; version=0.0.4'
+    response = if Gitlab::Metrics.prometheus_metrics_enabled?
+                 metrics_service.metrics_text
+               else
+                 help_page = help_page_url('administration/monitoring/prometheus/gitlab_metrics',
+                                           anchor: 'gitlab-prometheus-metrics'
+                                          )
+                 "# Metrics are disabled, see: #{help_page}\n"
+               end
+    render text: response, content_type: 'text/plain; version=0.0.4'
   end
 
   private
@@ -14,8 +20,4 @@ class MetricsController < ActionController::Base
   def metrics_service
     @metrics_service ||= MetricsService.new
   end
-
-  def validate_prometheus_metrics
-    render_404 unless Gitlab::Metrics.prometheus_metrics_enabled?
-  end
 end
diff --git a/changelogs/unreleased/pawel-show_empty_page_when_prometheus_metrics_are_disabled-35639.yml b/changelogs/unreleased/pawel-show_empty_page_when_prometheus_metrics_are_disabled-35639.yml
new file mode 100644
index 00000000000..987f7286244
--- /dev/null
+++ b/changelogs/unreleased/pawel-show_empty_page_when_prometheus_metrics_are_disabled-35639.yml
@@ -0,0 +1,5 @@
+---
+title: Make Prometheus metrics endpoint return empty response when metrics are disabled
+merge_request: 14490
+author:
+type: changed
diff --git a/spec/controllers/metrics_controller_spec.rb b/spec/controllers/metrics_controller_spec.rb
index 4aed2a25baa..9e8a37171ec 100644
--- a/spec/controllers/metrics_controller_spec.rb
+++ b/spec/controllers/metrics_controller_spec.rb
@@ -67,7 +67,8 @@ describe MetricsController do
         it 'returns proper response' do
           get :index
 
-          expect(response.status).to eq(404)
+          expect(response.status).to eq(200)
+          expect(response.body).to eq("# Metrics are disabled, see: http://test.host/help/administration/monitoring/prometheus/gitlab_metrics#gitlab-prometheus-metrics\n")
         end
       end
     end