Add custom vpc_cidr_index variable to avoid VPC CIDR collisions with …

…multiple environments

terraform/locals.tf

@@ -3,5 +3,5 @@ locals {
     Application = "aws-swan-demo"
     Environment = var.environment
   }
-  namespace = "aws-swan-demo-${var.environment}"
+  namespace       = "aws-swan-demo-${var.environment}"
 }

terraform/variables.tf

@@ -1,16 +1,22 @@
 variable "aws_region" {
   default     = "us-east-1"
-  description = "The AWS region name in which the main infrastructure should be deployed"
+  description = "The AWS region name in which the main infrastructure should be deployed."
   type        = string
 }
 
 variable "aws_replication_region" {
   default     = "us-west-2"
-  description = "The AWS replication region where resources are provisioned for failover"
+  description = "The AWS replication region where resources are provisioned for failover."
   type        = string
 }
 
+variable "vpc_cidr_index" {
+  default = 0
+  description = "The number of the second CIDR IP address segment to act as an index for multiple environment support. The default CIDR range is 10.0.0.0/16, so setting this to 1 would initialize the VPC to a CIDR range of 10.1.0.0/16. This is a negotiated stopgap solution to allow for the provisioning of multiple instances of the application in one region and avoid CIDR collisions."
+  type = number
+}
+
 variable "environment" {
-  description = "Name of the provisioned environment for namespacing purposes"
+  description = "Name of the provisioned environment for namespacing purposes."
   type = string
 }

terraform/vpc.tf

@@ -1,5 +1,5 @@
 resource "aws_vpc" "vpc" {
-  cidr_block           = "10.0.0.0/16"
+  cidr_block           = "10.${var.vpc_cidr_index}.0.0/16"
   enable_dns_support   = true
   enable_dns_hostnames = true
 
@@ -11,7 +11,7 @@ resource "aws_vpc" "vpc" {
 # Public subnets
 resource "aws_subnet" "public_1" {
   availability_zone = "${var.aws_region}a"
-  cidr_block = "10.0.1.0/24"
+  cidr_block = "10.${var.vpc_cidr_index}.1.0/24"
   map_public_ip_on_launch = true
   vpc_id = aws_vpc.vpc.id
 
@@ -22,7 +22,7 @@ resource "aws_subnet" "public_1" {
 
 resource "aws_subnet" "public_2" {
   availability_zone = "${var.aws_region}b"
-  cidr_block = "10.0.2.0/24"
+  cidr_block = "10.${var.vpc_cidr_index}.2.0/24"
   map_public_ip_on_launch = true
   vpc_id = aws_vpc.vpc.id
 
@@ -34,7 +34,7 @@ resource "aws_subnet" "public_2" {
 # Private subnets
 resource "aws_subnet" "private_1" {
   availability_zone = "${var.aws_region}a"
-  cidr_block = "10.0.3.0/24"
+  cidr_block = "10.${var.vpc_cidr_index}.3.0/24"
   vpc_id = aws_vpc.vpc.id
 
   tags = {
@@ -44,7 +44,7 @@ resource "aws_subnet" "private_1" {
 
 resource "aws_subnet" "private_2" {
   availability_zone = "${var.aws_region}b"
-  cidr_block = "10.0.4.0/24"
+  cidr_block = "10.${var.vpc_cidr_index}.4.0/24"
   vpc_id = aws_vpc.vpc.id
 
   tags = {