Suspected Bug: CDK fails Network Load Balancer deployment because ip-address-type is dual-stack, except it's not dual-stack

It seems the issue is occurring because your NLB currently only supports IPv4, but you are trying to add UDP listeners which require the NLB to be in dual-stack mode to support both IPv4 and IPv6.

A few things you can try:

• Check the AWS documentation on limitations of NLB listeners to confirm UDP listeners require dual-stack mode: https://docs.aws.amazon.com/elasticloadbalancing/latest/network/load-balancer-listeners.html
• Set the IP address type of the NLB to dual-stack using the CLI:

 aws elbv2 set-ip-address-type --load-balancer-arn load-balancer-arn --ip-address-type dualstack --region region

• Remove any existing listeners on the NLB before adding the new UDP listeners.
• Deploy the CDK stack again after setting the NLB to dual-stack mode. This should resolve the error about UDP listeners requiring dual-stack.
• Verify in the AWS console that the IP address type of the NLB is now dual-stack before and after deploying the CDK changes.

Thanks for the reply, but it seems that maybe you have misunderstood the issue. The error says that the NLB is dualstack (dualstack as in IPv4 and IPv6) while it is not. This same setup used to work fine and I'm inclined to think that maybe it's a bug in the current cdk release. The solution you propose is hard to test because the setup is in production and handles running traffic and I can't just remove the listeners. Setting up a test setup would be incredibly labour-intensive as it depends on some resources outside of my organisation. I don't understand why CDK keeps complaining about the load balancer being dualstack when it is not. And even after manually configuring it to be exclusively IPv4 the issue persists.

I have tried by the way to switch it over to dualstack from the awscli, the issue is that dualstack NLBs are not compatible with UDP listeners. So even if I detached the listeners and converted the NLB to dualstack and tried re-attaching the listeners, according to the docs it wouldn't work because UDP listeners need the NLB to be in IPv4 mode.