Merge branch 'mk-front-load-rails-slis' into 'master'

Move Rails SLI initialization to boot path

See merge request gitlab-org/gitlab!80059

app/controllers/metrics_controller.rb

@@ -7,7 +7,6 @@ class MetricsController < ActionController::Base
 
   def index
     response = if Gitlab::Metrics.prometheus_metrics_enabled?
-                 Gitlab::Metrics::RailsSlis.initialize_request_slis_if_needed!
                  metrics_service.metrics_text
                else
                  help_page = help_page_url('administration/monitoring/prometheus/gitlab_metrics',

doc/development/application_slis/index.md

@@ -57,31 +57,10 @@ Gitlab::Metrics::Sli.initialize_sli(:received_email, [
 ])
 ```
 
-Metrics must be initialized before they get
-scraped for the first time. This could be done at the start time of the
-process that will emit them, in which case we need to pay attention
-not to increase application's boot time too much. This is preferable
-if possible.
-
-Alternatively, if initializing would take too long, this can be done
-during the first scrape. We need to make sure we don't do it for every
-scrape. This can be done as follows:
-
-```ruby
-def initialize_request_slis_if_needed!
-  return if Gitlab::Metrics::Sli.initialized?(:rails_request_apdex)
-  Gitlab::Metrics::Sli.initialize_sli(:rails_request_apdex, possible_request_labels)
-end
-```
-
-Also pay attention to do it for the different metrics
-endpoints we have. Currently the
-[`WebExporter`](https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/metrics/exporter/web_exporter.rb)
-and the
-[`HealthController`](https://gitlab.com/gitlab-org/gitlab/blob/master/app/controllers/health_controller.rb)
-for Rails and
-[`SidekiqExporter`](https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/metrics/exporter/sidekiq_exporter.rb)
-for Sidekiq.
+Metrics must be initialized before they get scraped for the first time.
+This currently happens during the `on_master_start` [life-cycle event](https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/cluster/lifecycle_events.rb).
+Since this delays application readiness until metrics initialization returns, make sure the overhead
+this adds is understood and acceptable.
 
 ## Tracking operations for an SLI
 

lib/gitlab/metrics/exporter/web_exporter.rb

@@ -4,29 +4,10 @@ module Gitlab
   module Metrics
     module Exporter
       class WebExporter < BaseExporter
-        RailsMetricsInitializer = Struct.new(:app) do
-          def call(env)
-            Gitlab::Metrics::RailsSlis.initialize_request_slis_if_needed!
-
-            app.call(env)
-          end
-        end
-
         # This exporter is always run on master process
         def initialize(**options)
           super(Settings.monitoring.web_exporter, log_enabled: true, log_file: 'web_exporter.log', **options)
         end
-
-        private
-
-        def rack_app
-          app = super
-
-          Rack::Builder.app do
-            use RailsMetricsInitializer
-            run app
-          end
-        end
       end
     end
   end

lib/gitlab/metrics/rails_slis.rb

@@ -4,7 +4,7 @@ module Gitlab
   module Metrics
     module RailsSlis
       class << self
-        def initialize_request_slis_if_needed!
+        def initialize_request_slis!
           Gitlab::Metrics::Sli.initialize_sli(:rails_request_apdex, possible_request_labels) unless Gitlab::Metrics::Sli.initialized?(:rails_request_apdex)
           Gitlab::Metrics::Sli.initialize_sli(:graphql_query_apdex, possible_graphql_query_labels) unless Gitlab::Metrics::Sli.initialized?(:graphql_query_apdex)
         end

lib/gitlab/metrics/requests_rack_middleware.rb

@@ -62,6 +62,8 @@ module Gitlab
             http_requests_total.get({ method: method, status: status, feature_category: feature_category })
           end
         end
+
+        Gitlab::Metrics::RailsSlis.initialize_request_slis!
       end
 
       def call(env)

spec/controllers/metrics_controller_spec.rb

@@ -67,12 +67,6 @@ RSpec.describe MetricsController, :request_store do
         expect(response.body).to match(/^prometheus_counter 1$/)
       end
 
-      it 'initializes the rails request SLIs' do
-        expect(Gitlab::Metrics::RailsSlis).to receive(:initialize_request_slis_if_needed!).and_call_original
-
-        get :index
-      end
-
       context 'prometheus metrics are disabled' do
         before do
           allow(Gitlab::Metrics).to receive(:prometheus_metrics_enabled?).and_return(false)

spec/lib/gitlab/metrics/exporter/web_exporter_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-
-RSpec.describe Gitlab::Metrics::Exporter::WebExporter do
-  let(:exporter) { described_class.new }
-
-  before do
-    stub_config(
-      monitoring: {
-        web_exporter: {
-          enabled: true,
-          port: 0,
-          address: '127.0.0.1'
-        }
-      }
-    )
-
-    exporter.start
-  end
-
-  after do
-    exporter.stop
-  end
-
-  context 'when running server', :prometheus do
-    it 'initializes request metrics' do
-      expect(Gitlab::Metrics::RailsSlis).to receive(:initialize_request_slis_if_needed!).and_call_original
-
-      http = Net::HTTP.new(exporter.server.config[:BindAddress], exporter.server.config[:Port])
-      response = http.request(Net::HTTP::Get.new('/metrics'))
-
-      expect(response.body).to include('gitlab_sli:rails_request_apdex')
-    end
-  end
-end

spec/lib/gitlab/metrics/rails_slis_spec.rb

@@ -13,7 +13,7 @@ RSpec.describe Gitlab::Metrics::RailsSlis do
     allow(Gitlab::Graphql::KnownOperations).to receive(:default).and_return(Gitlab::Graphql::KnownOperations.new(%w(foo bar)))
   end
 
-  describe '.initialize_request_slis_if_needed!' do
+  describe '.initialize_request_slis!' do
     it "initializes the SLI for all possible endpoints if they weren't", :aggregate_failures do
       possible_labels = [
         {
@@ -41,7 +41,7 @@ RSpec.describe Gitlab::Metrics::RailsSlis do
       expect(Gitlab::Metrics::Sli).to receive(:initialize_sli).with(:rails_request_apdex, array_including(*possible_labels)).and_call_original
       expect(Gitlab::Metrics::Sli).to receive(:initialize_sli).with(:graphql_query_apdex, array_including(*possible_graphql_labels)).and_call_original
 
-      described_class.initialize_request_slis_if_needed!
+      described_class.initialize_request_slis!
     end
 
     it 'does not initialize the SLI if they were initialized already', :aggregate_failures do
@@ -49,13 +49,13 @@ RSpec.describe Gitlab::Metrics::RailsSlis do
       expect(Gitlab::Metrics::Sli).to receive(:initialized?).with(:graphql_query_apdex) { true }
       expect(Gitlab::Metrics::Sli).not_to receive(:initialize_sli)
 
-      described_class.initialize_request_slis_if_needed!
+      described_class.initialize_request_slis!
     end
   end
 
   describe '.request_apdex' do
     it 'returns the initialized request apdex SLI object' do
-      described_class.initialize_request_slis_if_needed!
+      described_class.initialize_request_slis!
 
       expect(described_class.request_apdex).to be_initialized
     end
@@ -63,7 +63,7 @@ RSpec.describe Gitlab::Metrics::RailsSlis do
 
   describe '.graphql_query_apdex' do
     it 'returns the initialized request apdex SLI object' do
-      described_class.initialize_request_slis_if_needed!
+      described_class.initialize_request_slis!
 
       expect(described_class.graphql_query_apdex).to be_initialized
     end