FIX: previously, 2 subnets are created regardless of number of AZs

vpc-subnets/vpc.tf

@@ -8,6 +8,34 @@ module "random" {
   source = "./m.random"
 }
 
+module "public-subnets" {
+  source = "hashicorp/subnets/cidr"
+
+  base_cidr_block = local.subnet_start[0]
+
+  networks = [
+    for az in data.aws_availability_zones.available.names :
+    {
+      name     = az
+      new_bits = 4
+    }
+  ]
+}
+
+module "private-subnets" {
+  source = "hashicorp/subnets/cidr"
+
+  base_cidr_block = local.subnet_start[1]
+
+  networks = [
+    for az in data.aws_availability_zones.available.names :
+    {
+      name     = az
+      new_bits = 4
+    }
+  ]
+}
+
 module "vpc01" {
   source  = "terraform-aws-modules/vpc/aws"
   version = "2.47.0"
@@ -15,8 +43,8 @@ module "vpc01" {
   name                 = "demo-vpc-${module.random.number}"
   cidr                 = var.vpc-cidr
   azs                  = data.aws_availability_zones.available.names
-  private_subnets      = cidrsubnets(local.subnet_start[0], 4, 4)
-  public_subnets       = cidrsubnets(local.subnet_start[1], 4, 4)
+  private_subnets      = values(module.public-subnets.network_cidr_blocks)
+  public_subnets       = values(module.private-subnets.network_cidr_blocks)
   enable_nat_gateway   = false
   single_nat_gateway   = true
   enable_dns_hostnames = true