title: Add documents to elasticsearch if it does not exists
body: <p>I transferred some data from a log generated every day to elasticsearch using logstash, and my logstash output section looks like :</p>
  
  <p><a href="https://i.stack.imgur.com/CZZ2p.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CZZ2p.png" alt="enter image description here"></a></p>
  
  <p>i keep the same id (id_ot) in both my log file and elasticsearch, but what i would like to do is : if the new coming id ( id_ot) already exists in elasticseach, so i will not insert it. How can i do that in logstash ?</p>
  
  <p>Any help would be really appriciated !</p>