The example below builds a dual-stack VPC with public and private subnets in 3 AZs. Each subnet calculates an IPv4 CIDR based on the netmask argument passed, and an IPv6 CIDR with a /64 prefix length. The public subnets build NAT gateways in each AZ but optionally can be switched to single_az. An Egress-only Internet gateway is created by using the variable
