title: Kafka message ordering during consumer rebalance
body: <p>How message ordering is ensured during consumer rebalance. Suppose initially we have four partitions : p1 , p2 , p3, p4  and two consumers c1 and c2 (in same Group). So each consumer gets two partitions for example c1 : p1, p2  and c2 : p3, p4.</p>
  
  <p>Now new consumers are added say c3 and c4, rebalancing happens so that each consumer gets one Partition like c1 : p1, c2:p2, c3:p3, c4:p4.</p>
  
  <p>During this time there are chances that consumer c1 might be processing the message from partition p2 (before rebalancing)</p>
  
  <p>and consumer c2 also starts processing p2 messages (after rebalancing)       </p>
  
  <p>Even though this is corner case, is this expected behaviour of message ordering ? </p>