Bash script rotates the public IP address of an Amazon EC2 instance.

ec2-ip-rotate.sh

#!/usr/bin/env bash

function error_exit
{
    echo "$1" 1>&2
    exit 1
}

case $1 in
    'start')
        SCHEDULE='*/10 * * * *' # every ten minutes
        (crontab -l 2> /dev/null; echo "$SCHEDULE $(pwd)/$(basename $0)") | crontab - ;;
    'stop')
        crontab -l | grep -v $(basename $0) | crontab - ;;
    *)
        INSTANCE=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
        OLD_IP=$(curl -s http://169.254.169.254/latest/meta-data/public-ipv4)
        OLD_ALLOCATION=$(aws ec2 describe-addresses --public-ips $OLD_IP --query Addresses[0].AllocationId --output text)

        if [ $? -ne 0 ]; then
            error_exit "Failed to retrieve the old allocation ID. Aborting."
        fi

        NEW_IP=$(aws ec2 allocate-address --query PublicIp --output text)

        if [ $? -ne 0 ]; then
            error_exit "Failed to allocate a new address. Aborting."
        fi

        echo ''
        echo "Old IP: $OLD_IP"
        echo "New IP: $NEW_IP"
        echo ''
        echo 'Associating new IP...'

        aws ec2 associate-address --instance-id $INSTANCE --public-ip $NEW_IP

        if [ $? -ne 0 ]; then
            aws ec2 release-address --public-ip $NEW_IP
            error_exit "Failed to associate the new IP address. Released the new IP and aborting."
        fi

        echo 'Releasing old IP...'

        aws ec2 release-address --allocation-id $OLD_ALLOCATION

        if [ $? -ne 0 ]; then
            error_exit "Failed to release the old IP address. Manual intervention required."
        fi
esac

# The EC2 instance needs an IAM role with the following policy attached:
# {
#     "Version": "2012-10-17",
#     "Statement": [
#         {
#             "Effect": "Allow",
#             "Action": [
#                 "ec2:DescribeAddresses",
#                 "ec2:AllocateAddress",
#                 "ec2:AssociateAddress",
#                 "ec2:ReleaseAddress"
#             ],
#             "Resource": "*"
#         }
#     ]
# }
# Remember to replace "*" with the ARNs of specific resources if necessary.