availabilityMode

Specifies whether to create a zonal (single-AZ) or regional (multi-AZ) NAT gateway. Defaults to zonal.

A zonal NAT gateway is a NAT Gateway that provides redundancy and scalability within a single availability zone. A regional NAT gateway is a single NAT Gateway that works across multiple availability zones (AZs) in your VPC, providing redundancy, scalability and availability across all the AZs in a Region.

For more information, see Regional NAT gateways for automatic multi-AZ expansion in the Amazon VPC User Guide.