Disable Sidekiq Exporter logs by default

These logs generate a lot of data, and they generally aren't that useful
in production.

Relates to
https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/11362

changelogs/unreleased/sh-disable-sidekiq-exporter-logs.yml

+---
+title: Disable Sidekiq Exporter logs by default
+merge_request: 42267
+author:
+type: changed

config/gitlab.yml.example

@@ -1136,6 +1136,7 @@ production: &base
     # Sidekiq exporter is webserver built in to Sidekiq to expose Prometheus metrics
     sidekiq_exporter:
     #  enabled: true
+    #  log_enabled: false
     #  address: localhost
     #  port: 8082
 

config/initializers/1_settings.rb

@@ -784,6 +784,7 @@ Settings.monitoring['ip_whitelist'] ||= ['127.0.0.1/8']
 Settings.monitoring['unicorn_sampler_interval'] ||= 10
 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
 Settings.monitoring['web_exporter'] ||= Settingslogic.new({})

doc/administration/logs.md

@@ -723,10 +723,15 @@ was initiated, such as `1509705644.log`
 
 ## `sidekiq_exporter.log` and `web_exporter.log`
 
-If Prometheus metrics and the Sidekiq Exporter are both enabled, Sidekiq will
-start a Web server and listen to the defined port (default: `8082`). Access logs
-will be generated in `/var/log/gitlab/gitlab-rails/sidekiq_exporter.log` for
-Omnibus GitLab packages or in `/home/git/gitlab/log/sidekiq_exporter.log` for
+If Prometheus metrics and the Sidekiq Exporter are both enabled, Sidekiq
+will start a Web server and listen to the defined port (default:
+`8082`). By default, Sidekiq Exporter access logs are disabled but can
+be enabled via the `sidekiq['exporter_log_enabled'] = true` option in `/etc/gitlab/gitlab.rb`
+for Omnibus installations, or via the `sidekiq_exporter.log_enabled` option
+in `gitlab.yml` for installations from source. When enabled,
+access logs will be generated in
+`/var/log/gitlab/gitlab-rails/sidekiq_exporter.log` for Omnibus GitLab
+packages or in `/home/git/gitlab/log/sidekiq_exporter.log` for
 installations from source.
 
 If Prometheus metrics and the Web Exporter are both enabled, Puma/Unicorn will

lib/gitlab/metrics/exporter/sidekiq_exporter.rb

@@ -12,7 +12,11 @@ module Gitlab
         end
 
         def log_filename
-          File.join(Rails.root, 'log', 'sidekiq_exporter.log')
+          if settings['log_enabled']
+            File.join(Rails.root, 'log', 'sidekiq_exporter.log')
+          else
+            File::NULL
+          end
         end
 
         private

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

@@ -15,6 +15,7 @@ RSpec.describe Gitlab::Metrics::Exporter::SidekiqExporter do
         monitoring: {
           sidekiq_exporter: {
             enabled: true,
+            log_enabled: false,
             port: 0,
             address: '127.0.0.1'
           }
@@ -25,6 +26,29 @@ RSpec.describe Gitlab::Metrics::Exporter::SidekiqExporter do
     it 'does start thread' do
       expect(exporter.start).not_to be_nil
     end
+
+    it 'does not enable logging by default' do
+      expect(exporter.log_filename).to eq(File::NULL)
+    end
+  end
+
+  context 'with logging enabled' do
+    before do
+      stub_config(
+        monitoring: {
+          sidekiq_exporter: {
+            enabled: true,
+            log_enabled: true,
+            port: 0,
+            address: '127.0.0.1'
+          }
+        }
+      )
+    end
+
+    it 'returns a valid log filename' do
+      expect(exporter.log_filename).to end_with('sidekiq_exporter.log')
+    end
   end
 
   context 'when port is already taken' do