use availability zones to determine subnets cidr blocks

Author: nerahou

main.tf

@@ -14,6 +14,7 @@
  * limitations under the License.
 */
 
+data "aws_region" "current" {}
 
 # VPC
 resource "aws_vpc" "quortex" {
@@ -38,13 +39,22 @@ resource "aws_default_security_group" "quortex" {
 }
 
 resource "aws_vpc_ipv4_cidr_block_association" "secondary" {
-  for_each   = var.vpc_secondary_cidrs
+  for_each   = toset([for index, az in var.availability_zones : cidrsubnet(var.vpc_secondary_cidr, 2, index)])
   vpc_id     = aws_vpc.quortex.id
   cidr_block = each.value
 }
 
 resource "aws_subnet" "quortex" {
-  for_each = var.subnets
+  for_each = merge([
+    for key, subnet in var.subnets : {
+      for index, az in var.availability_zones : "${key}-${data.aws_region.current.name}${az}" => {
+        "availability_zone" = "${data.aws_region.current.name}${az}",
+        "cidr"              = cidrsubnet(subnet.cidr, 2, index),
+        "public"            = subnet.public,
+        "tags"              = subnet.tags,
+      }
+    }
+  ]...)
 
   vpc_id                  = aws_vpc.quortex.id
   availability_zone       = each.value.availability_zone

variables.tf

@@ -20,12 +20,6 @@ variable "vpc_name" {
   default     = "quortex"
 }
 
-variable "vpc_secondary_cidrs" {
-  type        = set(string)
-  description = "IPv4 secondary CIDRs to add to the VPC."
-  default     = []
-}
-
 variable "cluster_name" {
   type        = string
   description = "The name of the EKS cluster. Will be used to set the kubernetes.io/cluster/<cluster-name> tag on the VPC and subnets. It is required for Kubernetes to discover them."
@@ -71,10 +65,10 @@ variable "vpc_cidr_block" {
 }
 
 variable "subnets" {
-  type        = map(object({ availability_zone = string, cidr = string, public = bool, tags = optional(map(string), {}) }))
+  type        = map(object({ cidr = string, public = bool, tags = optional(map(string), {}) }))
   description = <<EOT
 A map representing the subnets that need to be created. Each item should
-specify the subnet's Availability Zone, cidr block, whether the subnet
+specify the subnet's cidr block, whether the subnet
 should be public or not and optionally extra tags to add.
 EOT
 }
@@ -96,3 +90,14 @@ variable "tags" {
   description = "The tags (a map of key/value pairs) to be applied to created resources."
   default     = {}
 }
+
+variable "vpc_secondary_cidr" {
+  type        = string
+  description = "IPv4 secondary CIDR to add to the VPC."
+  default     = "100.64.0.0/16"
+}
+
+variable "availability_zones" {
+  type        = list(string)
+  description = "The availability zones to use."
+}