Hi @tmokmss , thanks for reaching out.

The property mapPublicIpOnLaunch in CDK docs states that -

The property mapPublicIpOnLaunch controls if a public IPv4 address will be assigned. This defaults to false for dual stack VPCs to avoid inadvertant costs of having the public address. However, a public IP must be enabled (or otherwise configured with BYOIP or IPAM) in order for services that rely on the address to function.

The ipv6AssignAddressOnCreation property controls the same behavior for the IPv6 address. It defaults to true.

Using IPv6 specific properties in an IPv4 only VPC will result in errors.

As mentioned in CDK Docs, not assigning public IP when mapPublicIpOnLaunch=false, is intentional as mentioned in here -

Disabling the auto-assigning of a public IPv4 address by default can avoid the cost of public IPv4 addresses starting 2/1/2024. For use cases that need an IPv4 address, the mapPublicIpOnLaunch property in subnetConfiguration can be set to auto-assign the IPv4 address. Note that private IPv4 address allocation will not be changed.

and one can always assign public Ip addresses manually, by using Elastic IP Addresses.

AFAIU, and if my understanding is correct, this is by design to keep it disabled. Please feel free to correct me if something is misunderstood.

I would also reach out to core team and request their insights on the implementation of this concept.
Thanks

Thanks @khushail for the investigation!

this is by design to keep it disabled

I'm afraid not. Without public IP addresses, NAT instances won't work. This is a surprising behavior because users expect NatProvider.instanceV2 just works as soon as the deployment finished. Forcing users to assign public ip address manally is clearly a sub-optimal solution.

So a straightforward solution would be to expose a prop to assign a public IP address to the NAT instance when configuring NatProvider.instanceV2. In Instance construct, we have associatePublicIpAddress prop, which we can expose in NatInstanceProps and pass it when defining an Instance construct (below code).

thanks @tmokmss for the clarification there. Your solution makes sense.