Move Prometheus presentation logic to PrometheusText

+ Use NullMetrics to mock metrics when unused
+ Use method_missing in NullMetrics mocking
+ Update prometheus gem to version that correctly uses transitive dependencies
+ Ensure correct folders are used in Multiprocess prometheus client tests.
+ rename Sessions controller's metric

3 files changed, 13 insertions, 10 deletions

diff --git a/app/controllers/metrics_controller.rb b/app/controllers/metrics_controller.rb
index 9bcd6f96b34..0e9a19c0b6f 100644
--- a/app/controllers/metrics_controller.rb
+++ b/app/controllers/metrics_controller.rb
@@ -5,10 +5,8 @@ class MetricsController < ActionController::Base
 
   before_action :validate_prometheus_metrics
 
-  def metrics
-    response = "#{metrics_service.health_metrics_text}\n#{metrics_service.prometheus_metrics_text}"
-
-    render text: response, content_type: 'text/plain; version=0.0.4'
+  def index
+    render text: metrics_service.metrics_text, content_type: 'text/plain; verssion=0.0.4'
   end
 
   private
diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index fc9de30f256..ab52b676e01 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -48,7 +48,7 @@ class SessionsController < Devise::SessionsController
   private
 
   def login_counter
-    @login_counter ||= Gitlab::Metrics.counter(:user_session_logins, 'User logins count')
+    @login_counter ||= Gitlab::Metrics.counter(:user_session_logins, 'User sign in count')
   end
 
   # Handle an "initial setup" state, where there's only one user, it's an admin,
diff --git a/app/services/metrics_service.rb b/app/services/metrics_service.rb
index 350c3639e92..0faa86a228b 100644
--- a/app/services/metrics_service.rb
+++ b/app/services/metrics_service.rb
@@ -12,18 +12,23 @@ class MetricsService
   end
 
   def health_metrics_text
-    results = CHECKS.flat_map(&:metrics)
+    metrics = CHECKS.flat_map(&:metrics)
 
-    types = results.map(&:name).uniq.map { |metric_name| "# TYPE #{metric_name} gauge" }
-    metrics = results.map(&method(:metric_to_prom_line))
+    formatter.marshal(metrics)
+  end
 
-    types.concat(metrics).join("\n")
+  def metrics_text
+    "#{health_metrics_text}\n#{prometheus_metrics_text}"
   end
 
   private
 
+  def formatter
+    @formatter ||= PrometheusText.new
+  end
+
   def multiprocess_metrics_path
-    Rails.root.join(ENV['prometheus_multiproc_dir'])
+    @multiprocess_metrics_path ||= Rails.root.join(ENV['prometheus_multiproc_dir'])
   end
 
   def metric_to_prom_line(metric)