AWS EC2 renew IPv4 address by stop-wait-start instance. (no Elastic IPs needed)

ec2-renew-ip.sh

#!/bin/bash

# From AWS doc
# https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-instance-addressing.html
# We release your instance's public IP address when it is stopped or terminated. 
# Your stopped instance receives a new public IP address when it is restarted.

PATH=$HOME/.local/bin:$PATH

instace_ids="i-1348636c" #change it
sleep_time=30 #change it bigger to prevent fails                                                                        

function getip()
{
    # https://unix.stackexchange.com/a/268612/267632
    aws ec2 describe-instances --instance-ids $instace_ids | grep PublicIpAddress | awk -F ":" '{print $2}' | sed 's/[",]//g' | sed 's/ //'
}

function sleeping()
{
    echo -n "Sleeping $sleep_time seconds"
    for (( i=0; i<$sleep_time; i++ )); do
        sleep 1
        echo -n "."
    done
    echo ""
}

oldip=$(getip)
echo "{\"oldip\":$oldip}"
aws ec2 stop-instances --instance-ids $instace_ids
sleeping
aws ec2 start-instances --instance-ids $instace_ids
sleeping
sleeping
aws ec2 start-instances --instance-ids $instace_ids
sleeping
sleeping
sleeping
aws ec2 start-instances --instance-ids $instace_ids
newip=$(getip)
echo "{\"newip\":$newip}"

changed=false
if [ $oldip != $newip ]; then
    changed=true
fi
echo "{\"changed\":\"$changed\",\"newIP\":\"$newip\",\"oldIP\":\"$oldip\"}"

Example if you want dynamic dns.
sudo crontab -e then add the following:

# After rebooting.
@reboot /usr/local/bin/cf-ddns.sh >> /var/log/cf-ddns.log 2>&1