Only load usage ping cron schedule for Sidekiq

Previously the initializer always loaded the `application_settings`
table in the initializer, even for Rake tasks (e.g. `rake
db:setup). This was done because the usage ping worker needed to load
the UUID of theins instance from the database to calculate the usage
ping schedule. However, cron schedules are only needed by Sidekiq, so we
can defer the calculation of this value in the Sidekiq initializer.

When loading application settings from the database, this should make it
possible for us to raise errors when the connection is not present since
this appears to be the only setting that is actually needed at init
time.

This came out of a discussion in
https://gitlab.com/gitlab-org/gitlab/issues/205640.

changelogs/unreleased/sh-avoid-current-settings-rake-task.yml

+---
+title: Only load usage ping cron schedule for Sidekiq
+merge_request: 25325
+author:
+type: other

config/initializers/1_settings.rb

@@ -446,7 +446,7 @@ Settings.cron_jobs['stuck_import_jobs_worker'] ||= Settingslogic.new({})
 Settings.cron_jobs['stuck_import_jobs_worker']['cron'] ||= '15 * * * *'
 Settings.cron_jobs['stuck_import_jobs_worker']['job_class'] = 'StuckImportJobsWorker'
 Settings.cron_jobs['gitlab_usage_ping_worker'] ||= Settingslogic.new({})
-Settings.cron_jobs['gitlab_usage_ping_worker']['cron'] ||= Settings.__send__(:cron_for_usage_ping)
+Settings.cron_jobs['gitlab_usage_ping_worker']['cron'] ||= nil # This is dynamically loaded in the sidekiq initializer
 Settings.cron_jobs['gitlab_usage_ping_worker']['job_class'] = 'GitlabUsagePingWorker'
 Settings.cron_jobs['stuck_merge_jobs_worker'] ||= Settingslogic.new({})
 Settings.cron_jobs['stuck_merge_jobs_worker']['cron'] ||= '0 */2 * * *'

config/initializers/sidekiq.rb

+# frozen_string_literal: true
+
 require 'sidekiq/web'
 
 def enable_reliable_fetch?
@@ -71,6 +73,8 @@ Sidekiq.configure_server do |config|
     Sidekiq::ReliableFetch.setup_reliable_fetch!(config)
   end
 
+  Gitlab.config.load_dynamic_cron_schedules!
+
   # Sidekiq-cron: load recurring jobs from gitlab.yml
   # UGLY Hack to get nested hash from settingslogic
   cron_jobs = JSON.parse(Gitlab.config.cron_jobs.to_json)

config/settings.rb

+# frozen_string_literal: true
+
 require 'settingslogic'
 require 'digest/md5'
 
@@ -143,6 +145,10 @@ class Settings < Settingslogic
       Gitlab::Application.secrets.db_key_base
     end
 
+    def load_dynamic_cron_schedules!
+      cron_jobs['gitlab_usage_ping_worker']['cron'] ||= cron_for_usage_ping
+    end
+
     private
 
     def base_url(config)

spec/config/settings_spec.rb

@@ -9,6 +9,12 @@ describe Settings do
     end
   end
 
+  describe '.load_dynamic_cron_schedules!' do
+    it 'generates a valid cron schedule' do
+      expect(Fugit::Cron.parse(described_class.load_dynamic_cron_schedules!)).to be_a(Fugit::Cron)
+    end
+  end
+
   describe '.attr_encrypted_db_key_base_truncated' do
     it 'is a string with maximum 32 bytes size' do
       expect(described_class.attr_encrypted_db_key_base_truncated.bytesize)