title: Upgrade Solrcloud 4.10.2 to 5.2.1
body: <p>I have SolrCloud 4.10.2 version setup with 4 nodes running successfully in the production.Now I want to upgrade this setup to 5.2.1 version.I want to make sure that my application accessing solr is not experiencing any downtime during upgrade.</p>
  
  <p>As of now I am thinking to nodes one by one.That means I will stop one node,upgrade it by replacing solr.war &amp; start it.Now my worry is will there be any problem till I upgrade other 3 nodes to 5.2.1 as there will be version mismatch between Solr nodes?</p>
  
  <p>How solr upgrade is handled in the industry?</p>