Explanation: In the EC2-Classic platform, when you associate an Elastic IP Address (EIP) with an instance, theinstance's current public IP address is released to the EC2-Classic public IP address pool. If youdisassociate an EIP from the instance, the instance is automatically assigned a new public IP addresswithin a few minutes. In addition, stopping the instance also disassociates the EIP from it. But in theEC2-VPC platform, when you associate an EIP with an instance in a default Virtual Private Cloud(VPC), or an instance in which you assigned a public IP to the eth0 network interface during launch,its current public IP address is released to the EC2-VPC public IP address pool. If you disassociate anEIP from the instance, the instance is automatically assigned a new public IP address within a fewminutes. However, if you have attached a second network interface to the instance, the instance isnot automatically assigned a new public IP address; you'll have to associate an EIP with it manually.The EIP remains associated with the instance when you stop it. Reference: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/elastic-ip-addresses-eip.html