title: Namenode with high availability vs zookeeper based leader selection
body: <p>I am reading 2 different things in Apache Hadoop documentation and cloudera's documentation.<br>
  Based on cloudera, we should set up namenode in high availability mode, i.e.: by defining primary and secondary namenode, but based on Hadoop documentation, this should automatically taken care by zookeeper and it should decide namenode among the available datanodes.</p>
  
  <p>Can anyone explain the difference and which one to use?</p>