Each EC2 instance you create has two IP addresses: Amazon’s private internal IP address, and the external IP address that Internet users will use to access the EC2 instance. By default, the IP addresses are dynamic, which means that each time the EC2 instance is stopped and restarted, the IP addresses for the EC2 instance change.

You can obtain static, or elastic, external IP addresses and associate them with EC2 instances. For example, if you are hosting My webMethods on an EC2 instance, you would associate an elastic IP address with the instance so users can connect to My webMethods. Conversely, if you are running your products in Amazon EC2 and a webMethods Broker is installed for the sole purpose of coordinating messaging among EC2 instances, you would typically not associate an elastic IP address with the webMethods Broker host EC2 instance.

Go to the NETWORK & SECURITY > Elastic IPs page, allocate a new elastic IP address, and then associate the address with an EC2 instance.

You can change the association of an elastic IP address from one EC2 instance to another. If you stop and start the associated EC2 instance from the AWS Management Console, you will have to associate the elastic IP address with the EC2 instance again. Any time you associate or re-associate an elastic IP address with an EC2 instance, you must update your DNS server with the IP address and the corresponding host name.