To meet the requirement of using only IPv6 for all EC2 instances while allowing outbound internet access and preventing inbound internet access, an egress-only internet gateway is the correct solution. An egress-only internet gateway allows outbound communication over IPv6 and blocks inbound communication, ensuring that the instances can access the internet but are not directly accessible from the internet.

Create an Egress-Only Internet Gateway:

Open the Amazon VPC console at Amazon VPC Console.

In the navigation pane, choose Egress-only internet gateways.

Choose Create egress-only internet gateway, and then attach it to your VPC.

Create a Custom Route Table:

In the VPC console, navigate to Route Tables.

Create a new route table or select an existing one.

Add a route with the destination set to ::/0 (which represents all IPv6 addresses) and the target set to the egress-only internet gateway.

Attach the Route Table to IPv6-Only Subnets:

Associate the route table with the IPv6-only subnets in your VPC.

This configuration ensures that your IPv6-only EC2 instances can access the internet while being protected from inbound internet traffic.

Egress-Only Internet Gateways

IPv6 Addresses