An advantage of using Amazon Elastic Compute Cloud (EC2) is the ability to start, stop, create, and terminate instances at any time. However, this flexibility creates a potential challenge with IP addresses. Restarting a stopped instance (or re-creating an instance after another instance is terminated) results in a new IP address.
To avoid this problem, you can allocate an Elastic IP address for an EC2 instance. An Elastic IP provides you a single IP address that you can associate with different EC2 instances over time. If you assign an Elastic IP address to an Amazon Elastic Compute Cloud instance, and you stop or terminate the instance, you can immediately associate the Elastic IP address to a new EC2 instance that contains the same content as the old instance. Your existing applications will not break, because the applications connect using the Elastic IP address, which did not change.
You can associate an Elastic IP address with a stand-alone ArcGIS Server site that contains one EC2 instance or an ArcGIS Enterprise deployment that has all components installed on a single EC2 instance.
An Elastic IP address is not the same as an Amazon Load Balancer. An Amazon Load Balancer helps you scale out a site by associating many EC2 instances at the same time under one web address. An Elastic IP address, on the other hand, can only be associated with one EC2 instance at a time.
Follow the instructions in the AWS documentation to allocate an Elastic IP address and associate it with an AWS instance.