Amazon Elastic Compute Cloud (EC2) : Elastic IP

Every time an Amazon EC2 instance is restarted, its public DNS name changes. If you want to use Amazon AWS to host your website, you need a way to map your domain name to an EC2 instance. That's when Amazon's Elastic IP Address comes to play. Elastic IP Address is similar to static IP address, with one key difference. A user can map an Elastic IP Address to any EC2 instance in the AWS console without having to wait for DNS to propagate the new binding.  An Elastic IP Address belongs to the account instance of an EC2 instance. To obtain an  Elastic IP Address, log into AWS management Console,  Click the EC2 tab, then click Elastic IPs link on the left panel.

Click Yes, Allocate to get a new Elastic IP.

Click the Associate Address to map the Elastic IP to an instance.

Pick up an instance from the dropdown box and click Yes, Associate button. Now your EC2 instance is associated with an Elastic IP.