title: Does RabbitMQ call the callback function for a consumer when it has some message for it?
body: <p>Does <a href="http://www.rabbitmq.com/getstarted.html" rel="noreferrer">RabbitMQ</a> call the callback function for a consumer when it has some message for it, or does the consumer have to poll the RabbitMQ client?</p>
  
  <p>So on the consumer side, if there is a PHP script, can RabbitMQ call it and pass the message/parameters to it. e.g. if rating is submitted on shard 1 and the aggregateRating table is on shard 2, then would RabbitMQ consumer on shard 2 trigger the script say aggRating.php and pass the parameters that were inserted in shard 1?</p>