Add toggles for private & public subnet creation

This lets users create only private (or only public) subnets. The CIDR
range is still divided as per usual, so you can change your mind later
with minimal disruption.

private.tf

@@ -17,7 +17,7 @@ locals {
 }
 
 resource "aws_subnet" "private" {
-  count             = local.enabled ? local.availability_zones_count : 0
+  count             = local.enabled && var.create_private_subnets ? local.availability_zones_count : 0
   vpc_id            = join("", data.aws_vpc.default.*.id)
   availability_zone = element(var.availability_zones, count.index)
 

public.tf

@@ -19,7 +19,7 @@ locals {
 }
 
 resource "aws_subnet" "public" {
-  count             = local.enabled ? local.availability_zones_count : 0
+  count             = local.enabled && var.create_public_subnets ? local.availability_zones_count : 0
   vpc_id            = join("", data.aws_vpc.default.*.id)
   availability_zone = element(var.availability_zones, count.index)
 

variables.tf

@@ -136,3 +136,15 @@ variable "root_block_device_encrypted" {
   default     = true
   description = "Whether to encrypt the root block device"
 }
+
+variable "create_public_subnets" {
+  type        = bool
+  default     = true
+  description = "Set to false to prevent the module from creating public subnets. Some of your CIDR block will still be reserved, so you can change this later without disruption."
+}
+
+variable "create_private_subnets" {
+  type        = bool
+  default     = true
+  description = "Set to false to prevent the module from creating private subnets. Some of your CIDR block will still be reserved, so you can change this later without disruption."
+}