This assumes you have already configured the aws command line tool. If not, check out my article on Getting Started with the AWS CLI.

An Elastic IP address is a static public IP address that is typically associated with one of your EC2 instances as a way to have a static public IP address that can be used to route traffic into your Amazon Web Services cluster. Typically, you will create a DNS A record to bind a hostname such as www.example.com to the elastic IP address. The DNS can be done using Amazon Web Services Route 53.

The aws ec2 describe-addresses command can be used to list the Elastic IP addresses you have associated to your EC2 instances. In this example, the Elastic IP address is 154.19.50.198.

~]$ aws ec2 describe-addresses
{
    "Addresses": [
        {
            "InstanceId": "i-09e2e375cf14807b2",
            "PublicIp": "154.19.50.198",
            "AllocationId": "eipalloc-0a5c72c343bc546b0",
            "AssociationId": "eipassoc-0b12eaaacc74f9e24",
            "Domain": "vpc",
            "NetworkInterfaceId": "eni-004a4335b85583ae2",
            "NetworkInterfaceOwnerId": "123456789012",
            "PrivateIpAddress": "172.31.19.227",
            "Tags": [
                {
                    "Key": "Name",
                    "Value": "haproxy-ip"
                }
            ],
            "PublicIpv4Pool": "amazon",
            "NetworkBorderGroup": "us-east-1"
        }
    ]
}

And here is an example of how to limit the output using the --query option.

aws ec2 describe-addresses --query 'Addresses[?PublicIp==`154.19.50.198`]'

And here is an example of how to limit the output using the --filters option. This will only work if the Elastic IP has Tags.

aws ec2 describe-addresses --filters "Name=tag-value,Values=haproxy-ip"

The aws route53 list-resource-record-sets command can be used to determine if there are any A records pointing to the Elastic IP address.

~]$ aws route53 list-resource-record-sets --hosted-zone-id Z056866DJM1OE9C45GH42
{
    "ResourceRecordSets": [
        {
            "Name": "example.com.",
            "Type": "NS",
            "TTL": 172800,
            "ResourceRecords": [
                {
                    "Value": "ns-550.awsdns-04.net."
                },
                {
                    "Value": "ns-499.awsdns-62.com."
                },
                {
                    "Value": "ns-1687.awsdns-18.co.uk."
                },
                {
                    "Value": "ns-1193.awsdns-21.org."
                }
            ]
        },
        {
            "Name": "example.com.",
            "Type": "SOA",
            "TTL": 900,
            "ResourceRecords": [
                {
                    "Value": "ns-550.awsdns-04.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400"
                }
            ]
        },
        {
            "Name": "foo.example.com.",
            "Type": "A",
            "TTL": 300,
            "ResourceRecords": [
                {
                    "Value": "154.19.50.198"
                }
            ]
        }
    ]
}