Schedule jobs

* Stalled jobs are checked every 5 minutes
* Failed jobs are retried every hour
* Old preview jobs are cleaned up daily

config/initializers/scheduler.rb

@@ -0,0 +1,18 @@
+require 'rufus-scheduler'
+
+# Don't schedule jobs in test environment or when running rake tasks
+unless defined?(Rails::Console) || Rails.env.test? || File.split($0).last == 'rake'
+  scheduler = Rufus::Scheduler.new
+
+  scheduler.every '5m' do
+    PreviewGenerationMonitor.check_stalled_jobs
+  end
+
+  scheduler.every '1h' do
+    PreviewGenerationMonitor.retry_failed
+  end
+
+  scheduler.every '1d' do
+    PreviewGenerationMonitor.cleanup_old_previews
+  end
+end