Expire application settings from cache at startup

If a DB migration occurs, there's a chance that the application settings are
loaded from the cache and provide stale values, causing Error 500s.
This ensures that at startup the settings are always refreshed.

Closes #3643

CHANGELOG

@@ -1,6 +1,7 @@
 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.3.0 (unreleased)
+  - Ensure cached application settings are refreshed at startup (Stan Hu)
   - Fix: Assignee selector is empty when 'Unassigned' is selected (Jose Corcuera)
   - Fix 500 error when update group member permission
 

app/models/application_setting.rb

@@ -73,15 +73,23 @@ class ApplicationSetting < ActiveRecord::Base
   end
 
   after_commit do
-    Rails.cache.write('application_setting.last', self)
+    Rails.cache.write(cache_key, self)
   end
 
   def self.current
-    Rails.cache.fetch('application_setting.last') do
+    Rails.cache.fetch(cache_key) do
       ApplicationSetting.last
     end
   end
 
+  def self.expire
+    Rails.cache.delete(cache_key)
+  end
+
+  def self.cache_key
+    'application_setting.last'
+  end
+
   def self.create_from_defaults
     create(
       default_projects_limit: Settings.gitlab['default_projects_limit'],

app/models/ci/application_setting.rb

@@ -14,11 +14,15 @@ module Ci
     extend Ci::Model
 
     after_commit do
-      Rails.cache.write('ci_application_setting.last', self)
+      Rails.cache.write(cache_key, self)
+    end
+
+    def self.expire
+      Rails.cache.delete(cache_key)
     end
 
     def self.current
-      Rails.cache.fetch('ci_application_setting.last') do
+      Rails.cache.fetch(cache_key) do
         Ci::ApplicationSetting.last
       end
     end
@@ -29,5 +33,9 @@ module Ci
         add_pusher: Settings.gitlab_ci['add_pusher'],
       )
     end
+
+    def self.cache_key
+      'ci_application_setting.last'
+    end
   end
 end

config/initializers/1_settings.rb

@@ -293,3 +293,7 @@ if Rails.env.test?
   Settings.gitlab['default_can_create_group'] = true
   Settings.gitlab['default_can_create_team']  = false
 end
+
+# Force a refresh of application settings at startup
+ApplicationSetting.expire
+Ci::ApplicationSetting.expire