title: Cassandra version upgrade
body: <p>I am currently using Cassandra 1.2.19 and cqlsh 3.1.8. I want to upgrade Cassandra version to 2.1.7. Which things do I need to keep in consideration for upgrading? </p>
  
  <p>If I upgrade the version, will there occur any problem to maintain the node, add new node or remove the node? </p>
  
  <p>Will secondary index work properly after upgrading? </p>
  
  <p>What is the step by step procedure to upgrade it?</p>