title: ElasticSearch Event Listener
body: <p>My target is to build an <em>MQTT publish/subscribe</em> like service by only exploiting Elasticsearch.</p>
  
  <p>The case study scenario I would like to implement is this:</p>
  
  <ol>
  <li><em>User A</em> create a message (document) inside the Elasticsearch index</li>
  <li><em>User B</em> is warned and updated about the new message on the index.</li>
  </ol>
  
  <p>I'm using plain java clients, since in Android I can't use the High Level Elastic search client.
  I have everything that allow me to send and read documents from the ES index, but I would like to find the best way to implement a subscription service for User B, without forcing him to poll for updates every few seconds.</p>
  
  <p>About this I don't know where to start. I didn't find any trigger/websocket service available in ES. Please help with some ideas / documentation.</p>