Amazon Web Services (AWS) announces the launch of primary IPv6 address in a Virtual Private Cloud (VPC), enabling customer to make the first IPv6 address associated with their elastic network interface (ENI) immutable. Once the first IPv6 address is made primary on the ENI, the IPv6 address cannot be removed as long as the ENI is attached to an instance or until the instance is terminated, effectively making the address immutable. The primary IPv6 address can be an Amazon provided IPv6 address or a Bring your own IP (IPv6) addresses.
Source:: Amazon AWS