Initialize http_requests_total label values

Add http method/status initilaization to the `http_requests_total`
counter. This is required to track error rates and error ratios.

For example, the ratio of 5xx requests to all requests.

    sum(rate(http_requests_total{status=~"5.."}[5m])
    /
    sum(rate(http_requests_total[5m])

Without the inialization, there would be no values for 5xx on small or
low traffic servers. This would lead to blank graphs.

https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/585Signed-off-by: Ben Kochie <bjk@gitlab.com>

changelogs/unreleased/bjk-http_requests_total_status_matrix.yml

+---
+title: Make sure the http_requests_total and http_request_duration_seconds metrics are not empty on application start
+merge_request: 45755
+author:
+type: fixed

config/initializers/7_prometheus_metrics.rb

@@ -70,7 +70,7 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
     Gitlab::Metrics.gauge(:deployments, 'GitLab Version', {}, :max).set({ version: Gitlab::VERSION }, 1)
 
     unless Gitlab::Runtime.sidekiq?
-      Gitlab::Metrics::RequestsRackMiddleware.initialize_http_request_duration_seconds
+      Gitlab::Metrics::RequestsRackMiddleware.initialize_metrics
     end
   rescue IOError => e
     Gitlab::ErrorTracking.track_exception(e)

lib/gitlab/metrics/requests_rack_middleware.rb

@@ -3,7 +3,15 @@
 module Gitlab
   module Metrics
     class RequestsRackMiddleware
-      HTTP_METHODS = %w(delete get head options patch post put).to_set.freeze
+      HTTP_METHODS = {
+        "delete" => %w(200 202 204 303 400 401 403 404 500 503),
+        "get" => %w(200 204 301 302 303 304 307 400 401 403 404 410 422 429 500 503),
+        "head" => %w(200 204 301 302 303 401 403 404 410 500),
+        "options" => %w(200 404),
+        "patch" => %w(200 202 204 400 403 404 409 416 500),
+        "post" => %w(200 201 202 204 301 302 303 304 400 401 403 404 406 409 410 412 422 429 500 503),
+        "put" => %w(200 202 204 400 401 403 404 405 406 409 410 422 500)
+      }.freeze
 
       HEALTH_ENDPOINT = /^\/-\/(liveness|readiness|health|metrics)\/?$/.freeze
 
@@ -14,8 +22,8 @@ module Gitlab
         @app = app
       end
 
-      def self.http_request_total
-        @http_request_total ||= ::Gitlab::Metrics.counter(:http_requests_total, 'Request count')
+      def self.http_requests_total
+        @http_requests_total ||= ::Gitlab::Metrics.counter(:http_requests_total, 'Request count')
       end
 
       def self.rack_uncaught_errors_count
@@ -31,15 +39,31 @@ module Gitlab
         @http_health_requests_total ||= ::Gitlab::Metrics.counter(:http_health_requests_total, 'Health endpoint request count')
       end
 
-      def self.initialize_http_request_duration_seconds
-        HTTP_METHODS.each do |method|
+      def self.initialize_metrics
+        # This initialization is done to avoid gaps in scraped metrics after
+        # restarts. It makes sure all counters/histograms are available at
+        # process start.
+        #
+        # For example `rate(http_requests_total{status="500"}[1m])` would return
+        # no data until the first 500 error would occur.
+
+        # The list of feature categories is currently not needed by the application
+        # anywhere else. So no need to keep these in memory forever.
+        # Doing it here, means we're only reading the file on boot.
+        feature_categories = YAML.load_file(Rails.root.join('config', 'feature_categories.yml')).map(&:strip).uniq << FEATURE_CATEGORY_DEFAULT
+
+        HTTP_METHODS.each do |method, statuses|
           http_request_duration_seconds.get({ method: method })
+
+          statuses.product(feature_categories) do |status, feature_category|
+            http_requests_total.get({ method: method, status: status, feature_category: feature_category })
+          end
         end
       end
 
       def call(env)
         method = env['REQUEST_METHOD'].downcase
-        method = 'INVALID' unless HTTP_METHODS.include?(method)
+        method = 'INVALID' unless HTTP_METHODS.key?(method)
         started = Time.now.to_f
         health_endpoint = health_endpoint?(env['PATH_INFO'])
         status = 'undefined'
@@ -61,9 +85,13 @@ module Gitlab
           raise
         ensure
           if health_endpoint
-            RequestsRackMiddleware.http_health_requests_total.increment(status: status, method: method)
+            RequestsRackMiddleware.http_health_requests_total.increment(status: status.to_s, method: method)
           else
-            RequestsRackMiddleware.http_request_total.increment(status: status, method: method, feature_category: feature_category.presence || FEATURE_CATEGORY_DEFAULT)
+            RequestsRackMiddleware.http_requests_total.increment(
+              status: status.to_s,
+              method: method,
+              feature_category: feature_category.presence || FEATURE_CATEGORY_DEFAULT
+            )
           end
         end
       end

spec/lib/gitlab/metrics/requests_rack_middleware_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
+RSpec.describe Gitlab::Metrics::RequestsRackMiddleware, :aggregate_failures do
   let(:app) { double('app') }
 
   subject { described_class.new(app) }
@@ -21,20 +21,15 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
         allow(app).to receive(:call).and_return([200, nil, nil])
       end
 
-      it 'increments requests count' do
-        expect(described_class).to receive_message_chain(:http_request_total, :increment).with(method: 'get', status: 200, feature_category: 'unknown')
-
-        subject.call(env)
-      end
-
       RSpec::Matchers.define :a_positive_execution_time do
         match { |actual| actual > 0 }
       end
 
-      it 'measures execution time' do
+      it 'tracks request count and duration' do
+        expect(described_class).to receive_message_chain(:http_requests_total, :increment).with(method: 'get', status: '200', feature_category: 'unknown')
         expect(described_class).to receive_message_chain(:http_request_duration_seconds, :observe).with({ method: 'get' }, a_positive_execution_time)
 
-        Timecop.scale(3600) { subject.call(env) }
+        subject.call(env)
       end
 
       context 'request is a health check endpoint' do
@@ -44,15 +39,10 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
               env['PATH_INFO'] = path
             end
 
-            it 'increments health endpoint counter rather than overall counter' do
-              expect(described_class).to receive_message_chain(:http_health_requests_total, :increment).with(method: 'get', status: 200)
-              expect(described_class).not_to receive(:http_request_total)
-
-              subject.call(env)
-            end
-
-            it 'does not record the request duration' do
+            it 'increments health endpoint counter rather than overall counter and does not record duration' do
               expect(described_class).not_to receive(:http_request_duration_seconds)
+              expect(described_class).not_to receive(:http_requests_total)
+              expect(described_class).to receive_message_chain(:http_health_requests_total, :increment).with(method: 'get', status: '200')
 
               subject.call(env)
             end
@@ -67,14 +57,9 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
               env['PATH_INFO'] = path
             end
 
-            it 'increments overall counter rather than health endpoint counter' do
-              expect(described_class).to receive_message_chain(:http_request_total, :increment).with(method: 'get', status: 200, feature_category: 'unknown')
+            it 'increments regular counters and tracks duration' do
+              expect(described_class).to receive_message_chain(:http_requests_total, :increment).with(method: 'get', status: '200', feature_category: 'unknown')
               expect(described_class).not_to receive(:http_health_requests_total)
-
-              subject.call(env)
-            end
-
-            it 'records the request duration' do
               expect(described_class)
                 .to receive_message_chain(:http_request_duration_seconds, :observe)
                       .with({ method: 'get' }, a_positive_execution_time)
@@ -88,26 +73,18 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
 
     context '@app.call throws exception' do
       let(:http_request_duration_seconds) { double('http_request_duration_seconds') }
+      let(:http_requests_total) { double('http_requests_total') }
 
       before do
         allow(app).to receive(:call).and_raise(StandardError)
         allow(described_class).to receive(:http_request_duration_seconds).and_return(http_request_duration_seconds)
+        allow(described_class).to receive(:http_requests_total).and_return(http_requests_total)
       end
 
-      it 'increments exceptions count' do
+      it 'tracks the correct metrics' do
         expect(described_class).to receive_message_chain(:rack_uncaught_errors_count, :increment)
-
-        expect { subject.call(env) }.to raise_error(StandardError)
-      end
-
-      it 'increments requests count' do
-        expect(described_class).to receive_message_chain(:http_request_total, :increment).with(method: 'get', status: 'undefined', feature_category: 'unknown')
-
-        expect { subject.call(env) }.to raise_error(StandardError)
-      end
-
-      it "does't measure request execution time" do
-        expect(described_class.http_request_duration_seconds).not_to receive(:increment)
+        expect(described_class).to receive_message_chain(:http_requests_total, :increment).with(method: 'get', status: 'undefined', feature_category: 'unknown')
+        expect(described_class.http_request_duration_seconds).not_to receive(:observe)
 
         expect { subject.call(env) }.to raise_error(StandardError)
       end
@@ -119,8 +96,9 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
           allow(app).to receive(:call).and_return([200, { described_class::FEATURE_CATEGORY_HEADER => 'issue_tracking' }, nil])
         end
 
-        it 'adds the feature category to the labels for http_request_total' do
-          expect(described_class).to receive_message_chain(:http_request_total, :increment).with(method: 'get', status: 200, feature_category: 'issue_tracking')
+        it 'adds the feature category to the labels for http_requests_total' do
+          expect(described_class).to receive_message_chain(:http_requests_total, :increment).with(method: 'get', status: '200', feature_category: 'issue_tracking')
+          expect(described_class).not_to receive(:http_health_requests_total)
 
           subject.call(env)
         end
@@ -128,8 +106,8 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
         it 'does not record a feature category for health check endpoints' do
           env['PATH_INFO'] = '/-/liveness'
 
-          expect(described_class).to receive_message_chain(:http_health_requests_total, :increment).with(method: 'get', status: 200)
-          expect(described_class).not_to receive(:http_request_total)
+          expect(described_class).to receive_message_chain(:http_health_requests_total, :increment).with(method: 'get', status: '200')
+          expect(described_class).not_to receive(:http_requests_total)
 
           subject.call(env)
         end
@@ -141,21 +119,37 @@ RSpec.describe Gitlab::Metrics::RequestsRackMiddleware do
         end
 
         it 'sets the feature category to unknown' do
-          expect(described_class).to receive_message_chain(:http_request_total, :increment).with(method: 'get', status: 200, feature_category: 'unknown')
+          expect(described_class).to receive_message_chain(:http_requests_total, :increment).with(method: 'get', status: '200', feature_category: 'unknown')
+          expect(described_class).not_to receive(:http_health_requests_total)
 
           subject.call(env)
         end
       end
     end
 
-    describe '.initialize_http_request_duration_seconds' do
-      it "sets labels" do
+    describe '.initialize_metrics', :prometheus do
+      it "sets labels for http_requests_total" do
+        feature_categories = YAML.load_file(Rails.root.join('config', 'feature_categories.yml')).map(&:strip) << described_class::FEATURE_CATEGORY_DEFAULT
         expected_labels = []
-        described_class::HTTP_METHODS.each do |method|
-          expected_labels << { method: method }
+
+        described_class::HTTP_METHODS.each do |method, statuses|
+          statuses.each do |status|
+            feature_categories.each do |feature_category|
+              expected_labels << { method: method.to_s, status: status.to_s, feature_category: feature_category.to_s }
             end
+          end
+        end
+
+        described_class.initialize_metrics
+
+        expect(described_class.http_requests_total.values.keys).to contain_exactly(*expected_labels)
+      end
+
+      it 'sets labels for http_request_duration_seconds' do
+        expected_labels = described_class::HTTP_METHODS.keys.map { |method| { method: method } }
+
+        described_class.initialize_metrics
 
-        described_class.initialize_http_request_duration_seconds
         expect(described_class.http_request_duration_seconds.values.keys).to include(*expected_labels)
       end
     end