title: How to safely upgrade server OS version that running Hadoop Namenode?
body: <h1>env</h1>
  <p>hadoop 3.2.1 version</p>
  <h1>question</h1>
  <p>I'm operating a Hadoop cluster with ha configuration.<br>
  I have to upgrade my os version of namenode server. Cent 6 to 7.<br>
  zkfc, journalnode, resourcemanager and namenode daemon are located on each ha server.<br>
  After shutting down all daemons from the standby server, I want to work in a way that upgrades the os.<br>
  My scenario</p>
  <ol>
  <li>shut down hadoop daemons of standby server</li>
  <li>os upgrade</li>
  <li>recover standby server daemons</li>
  <li>haadmin failover</li>
  <li>repeat</li>
  </ol>
  <p>Are there any anticipated problems?<br>
  I wonder if there is better way other than this one.</p>