title: Clarification of nginx and load balancing needed
body: <p>I'm now reading design of Instagram and I found such a description of their load balancing system.</p>
  
  <blockquote>
    <p>Every request to Instagram servers goes through load balancing machines; we used to run 2 nginx machines and DNS Round-Robin between them. The downside of this approach is the time it takes for DNS to update in case one of the machines needs to get decomissioned. Recently, we moved to using Amazon’s Elastic Load Balancer, with 3 NGINX instances behind it that can be swapped in and out (and are automatically taken out of rotation if they fail a health check). We also terminate our SSL at the ELB level, which lessens the CPU load on nginx. We use Amazon’s Route53 for DNS, which they’ve recently added a pretty good GUI tool for in the AWS console.</p>
  </blockquote>
  
  <p>The question is. Am I right that for now they have a DNS Server which uses RR to decide on which nginx server to send the request. And each of this nginx servers at their turn resends the request to a cluster?</p>
  
  <p>And the second question is. What the difference between nginx and load balancer. Why cannot we use nginx instead?</p>