Allow instantiating SidekiqExporter with settings

Going forward, we will be running several instances
of this server in separate processes, with different
sets of configuration (most notably, different ports)

This change merely prepares the code base for this;
since we default the new settings to the existing
exporter settings, it should be a no-op.

config/gitlab.yml.example

@@ -1260,6 +1260,12 @@ production: &base
     #  address: localhost
     #  port: 8082
 
+    sidekiq_health_checks:
+    #  enabled: true
+    #  log_enabled: false
+    #  address: localhost
+    #  port: 8082
+
     # Web exporter is a dedicated Rack server running alongside Puma to expose Prometheus metrics
     # It runs alongside the `/metrics` endpoints to ease the publish of metrics
     web_exporter:

config/initializers/1_settings.rb

@@ -919,11 +919,23 @@ Settings.webpack.dev_server['https']   ||= false
 #
 Settings['monitoring'] ||= Settingslogic.new({})
 Settings.monitoring['ip_whitelist'] ||= ['127.0.0.1/8']
+
 Settings.monitoring['sidekiq_exporter'] ||= Settingslogic.new({})
 Settings.monitoring.sidekiq_exporter['enabled'] ||= false
 Settings.monitoring.sidekiq_exporter['log_enabled'] ||= false
 Settings.monitoring.sidekiq_exporter['address'] ||= 'localhost'
 Settings.monitoring.sidekiq_exporter['port'] ||= 8082
+
+# TODO: Once we split out health checks from SidekiqExporter, we
+# should not let this default to the same settings anymore; we only
+# do this for back-compat currently.
+# https://gitlab.com/gitlab-org/gitlab/-/issues/345804
+Settings.monitoring['sidekiq_health_checks'] ||= Settingslogic.new({})
+Settings.monitoring.sidekiq_health_checks['enabled'] ||= Settings.monitoring.sidekiq_exporter['enabled']
+Settings.monitoring.sidekiq_health_checks['log_enabled'] ||= Settings.monitoring.sidekiq_exporter['log_enabled']
+Settings.monitoring.sidekiq_health_checks['address'] ||= Settings.monitoring.sidekiq_exporter['address']
+Settings.monitoring.sidekiq_health_checks['port'] ||= Settings.monitoring.sidekiq_exporter['port']
+
 Settings.monitoring['web_exporter'] ||= Settingslogic.new({})
 Settings.monitoring.web_exporter['enabled'] ||= false
 Settings.monitoring.web_exporter['address'] ||= 'localhost'

config/initializers/7_prometheus_metrics.rb

@@ -31,11 +31,17 @@ end
 if Gitlab::Runtime.sidekiq? && (!ENV['SIDEKIQ_WORKER_ID'] || ENV['SIDEKIQ_WORKER_ID'] == '0')
   # The single worker outside of a sidekiq-cluster, or the first worker (sidekiq_0)
   # in a cluster of processes, is responsible for serving health checks.
+  #
+  # Do not clean the metrics directory here - the supervisor script should
+  # have already taken care of that.
   Sidekiq.configure_server do |config|
     config.on(:startup) do
-      # Do not clean the metrics directory here - the supervisor script should
-      # have already taken care of that
-      Gitlab::Metrics::Exporter::SidekiqExporter.instance.start
+      # In https://gitlab.com/gitlab-org/gitlab/-/issues/345804 we are looking to
+      # only serve health-checks from a worker process; for backwards compatibility
+      # we still go through the metrics exporter server, but start to configure it
+      # with the new settings keys.
+      exporter_settings = Settings.monitoring.sidekiq_health_checks
+      Gitlab::Metrics::Exporter::SidekiqExporter.instance(exporter_settings).start
     end
   end
 end

lib/gitlab/metrics/exporter/base_exporter.rb

@@ -11,12 +11,14 @@ module Gitlab
 
         attr_accessor :readiness_checks
 
-        def enabled?
-          settings.enabled
+        def initialize(settings, **options)
+          super(**options)
+
+          @settings = settings
         end
 
-        def settings
-          raise NotImplementedError
+        def enabled?
+          settings.enabled
         end
 
         def log_filename
@@ -25,6 +27,8 @@ module Gitlab
 
         private
 
+        attr_reader :settings
+
         def start_working
           logger = WEBrick::Log.new(log_filename)
           logger.time_format = "[%Y-%m-%dT%H:%M:%S.%L%z]"

lib/gitlab/metrics/exporter/sidekiq_exporter.rb

@@ -4,10 +4,6 @@ module Gitlab
   module Metrics
     module Exporter
       class SidekiqExporter < BaseExporter
-        def settings
-          Settings.monitoring.sidekiq_exporter
-        end
-
         def log_filename
           if settings['log_enabled']
             File.join(Rails.root, 'log', 'sidekiq_exporter.log')

lib/gitlab/metrics/exporter/web_exporter.rb

@@ -27,7 +27,7 @@ module Gitlab
 
         # This exporter is always run on master process
         def initialize
-          super
+          super(Settings.monitoring.web_exporter)
 
           # DEPRECATED:
           # these `readiness_checks` are deprecated
@@ -39,10 +39,6 @@ module Gitlab
           ]
         end
 
-        def settings
-          Gitlab.config.monitoring.web_exporter
-        end
-
         def log_filename
           File.join(Rails.root, 'log', 'web_exporter.log')
         end

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

@@ -3,9 +3,9 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Metrics::Exporter::BaseExporter do
-  let(:exporter) { described_class.new }
-  let(:log_filename) { File.join(Rails.root, 'log', 'sidekiq_exporter.log') }
   let(:settings) { double('settings') }
+  let(:exporter) { described_class.new(settings) }
+  let(:log_filename) { File.join(Rails.root, 'log', 'sidekiq_exporter.log') }
 
   before do
     allow_any_instance_of(described_class).to receive(:log_filename).and_return(log_filename)

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

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Metrics::Exporter::SidekiqExporter do
-  let(:exporter) { described_class.new }
+  let(:exporter) { described_class.new(Settings.monitoring.sidekiq_exporter) }
 
   after do
     exporter.stop