title: How can I create a computed field in an index in elasticsearch?
body: <p>How can I compute a new field for an existing index in Elastic Search?</p>
  
  <p>I have these requirements for the computed field: </p>
  
  <ul>
  <li>It should be computed and stored together with the other fields, not computed dynamically. </li>
  <li>It should be computed for all historic records, not just new records coming in. </li>
  </ul>