AWS Removes NAT Gateway’s Dependence on Internet Gateway for Private Communications

You can now launch NAT Gateways in your Amazon Virtual Private Cloud (VPC) without associating an internet gateway to your VPC. Internet Gateway is required to provide internet access to the NAT Gateway. However, some customers use their NAT Gateways with Transit Gateway or virtual private gateway to communicate privately with other VPCs or on-premises environments and thus, do not need an internet gateway attached to their VPCs.

Source:: Amazon AWS