Issue #2: Full solution

variables-2.tf

variable "cidr_ab" {
    type = map
    default = {
        development     = "172.22"
        qa              = "172.24"
        staging         = "172.26"
        production      = "172.28"
    }
}

locals {
    private_subnets         = [
        "${lookup(var.cidr_ab, var.environment)}.1.0/24",
        "${lookup(var.cidr_ab, var.environment)}.2.0/24",
        "${lookup(var.cidr_ab, var.environment)}.3.0/24"
    ]

    database_subnets        = [
        "${lookup(var.cidr_ab, var.environment)}.11.0/24",
        "${lookup(var.cidr_ab, var.environment)}.12.0/24",
        "${lookup(var.cidr_ab, var.environment)}.13.0/24"
    ]

    public_subnets          = [
        "${lookup(var.cidr_ab, var.environment)}.64.0/24",
        "${lookup(var.cidr_ab, var.environment)}.65.0/24",
        "${lookup(var.cidr_ab, var.environment)}.66.0/24"
    ]
}

data "aws_availability_zones" "available" {
    state = "available"
}

locals {
    availability_zones = data.aws_availability_zones.available.names
}

variable "environment" {
    type = string
    description = "Options: development, qa, staging, production"
}