Elastic IP

here is the information on how to do it: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/elastic-ip-addresses-eip.html#using-instance-addressing-eips-allocating

Note An Elastic IP address doesn’t incur charges as long as the following conditions are true:

The Elastic IP address is associated with an EC2 instance. The instance associated with the Elastic IP address is running. The instance has only one Elastic IP address attached to it.