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

1 files changed, 10 insertions, 2 deletions

diff --git a/app/models/application_setting.rb b/app/models/application_setting.rb
index b2d5fe1558f..3df8135acf1 100644
--- a/app/models/application_setting.rb
+++ b/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'],