aws_availability_zone

variable "${region_number}" {
   # Arbitrary mapping of region name to number to use in
   # a VPC's CIDR prefix.
   default = {
       us-east-1      = 1
       us-west-2      = 3
       us-west-1      = 2
       eu-central-1   = 4
       ap-northeast-1 = 5
   }
}

variable "${az_number}" {
   # Assign a number to each AZ letter used in our configuration
   default = {
       a = 1
       b = 2
       c = 3
       d = 4
       e = 5
       f = 6
   }
}

# Retrieve the AZ where we want to create network resources
# This must be in the region selected on the AWS provider.
data "aws_availability_zone" "${example}" {
   name = "eu-central-1a"
}

# Create a VPC for the region associated with the AZ
resource "aws_vpc" "${example}" {
   cidr_block = "\${cidrsubnet("10.0.0.0/8", 4, var.${region_number}[data.aws_availability_zone.${example}.region])}"
}

# Create a subnet for the AZ within the regional VPC
resource "aws_subnet" "${example}" {
   vpc_id     = "${aws_vpc.${example}.id}"
   cidr_block = "$\{cidrsubnet(aws_vpc.${example}.cidr_block, 4, var.${az_number}[data.aws_availability_zone.name_suffix])}"
}