title: How does AWS know which instance i´m SSH:ing into?
body: <p>When I SSH into an Amazon instance without an elastic IP I use the public DNS name that is typically of the form ec2-79-125-100-3.eu-west-1.compute.amazonaws.com.</p>
  
  <p>Is that DNS name always resolved into the same IP? I assume not, because otherwise there would be no point in buying elastic IP:s. But then what is then the point of including the IP address in the DNS name?</p>
  
  <p>Also, since the IP that the DNS name resolves into is shared by many instances, how does Amazon know exactly which of those instances I'm ssh:ing into?</p>