AWS has begun charging approximately $4 per month for each public IPv4 address in AWS accounts.
This has led to an additional few hundred dollars in AWS expenses in our case. So, I spent a day
to configuring most of our EC2 instances to use IPv6.
Follow this AWS Guide
for a one-time setup per region.
At this point, your EC2 instance will have an associated IPv6 address. However, your IPv4 address will still be present.
Let's remove it.
Repeat steps 2 - 5 for all of your instances.