title: is it atomic stack-update in aws cloudformation?
body: <p>Let's say I have a stack consisting of </p>
  
  <ol>
  <li>ec2 instances as an application server</li>
  <li>one ELB as a load balancer</li>
  <li>two Elasticsearch nodes</li>
  </ol>
  
  <p>Then, if I update the stack for any reason, maybe to increase the number of the application servers, are all the new components made ready in parallel to my current stack and my current stack is replaced with the new one at once, like atomic operations in database systems?</p>
  
  <p>Because this reduction involves de-sharding the existing data in Elasticsearch, does the same procedure applies even if I reduce the number of Elasticsearch nodes? </p>