The Elastic IP address
As discussed in the earlier section, public IP addresses assigned to the EC2 instance can change when an EC2 instance is stopped and started. An Elastic IP address is a static IP address specifically designed for the dynamic nature of cloud computing. Public IPs and Elastic IP addresses are both public, and they both allow an EC2 instance to communicate over the internet. The Elastic IP address and public IP addresses differ in how long they are associated with the specific EC2 instance. When you stop an EC2 instance, the public IP address is released back to the Amazon public pool, and when you restart an instance, you get a new public IP address for your EC2 instance from the Amazon pool. The Elastic IP address is allocated in the AWS account and associated with an EC2 instance until it's disassociated from it. AWS will charge you for an Elastic IP address if it is associated with an instance that is not running.
A common reason to use an Elastic IP address is the...