title: AWS Elastic Load Balancer and multiple availability zones
body: <p>I want to understand how ELB load balances between multiple <strong><em>availability zones</em></strong>. For example, if I have 4 instances (<code>a1, a2, a3, a4</code>) in zone <code>us-east-1a</code> and a single instance <code>d1</code> in <code>us-east-1d</code> behind an ELB, how is the traffic distributed between the two availability zones? i.e., would <code>d1</code> get nearly 50% of all the traffic or <code>1/5th</code> of the traffic?</p>