Instances that you launch into a default subnet receive both a public IP address and a private IP address. Instances in a default subnet also receive both public and private DNS hostnames. Instances that you launch into a nondefault subnet in a default VPC don't receive a public IP address or a DNShostname. You can change your subnet's default public IP addressing behavior. Reference: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/default-vpc.html