title: Why do we need private subnet in VPC?
body: <p>There are <a href="http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Scenarios.html" rel="noreferrer">4 scenarios</a> in AWS VPC configure. But let's look at these two:</p>
  
  <ul>
  <li>Scenario 1: 1 public subnet. </li>
  <li>Scenario 2: 1 public subnet and 1 private subnet.</li>
  </ul>
  
  <p>Since any instance launched in public subnet does not have EIP (unless it's assigned), it is already not addressable from the Internet. Then:</p>
  
  <ul>
  <li>Why is there a need for private subnet?</li>
  <li>What exactly are the differences between private and public subnets?</li>
  </ul>