title: [[Django Celery]] Celery blocked doing IO tasks
body: <p>I use celery to do some IO tasks, such as grab remote image, sending email to users.
  But celery sometimes blocked with no logs. At this time, it won't do any task i send. I have to restart it, it begin to work where it blocked. </p>
  
  <p>It puzzles me for a very long time. What can i do ? And what is the best practice for distributing IO tasks with celery?</p>