Add secondary CIDR block support (#163)

* Add secondary CIDR block support using a local variable to derive the vpc id to ensure the CIDR block operations are applied before the CIDR operations

* Add secondary cidr block outputs to module output

* Add the wonderful examples from matthiasr's PR located at https://github.com/terraform-aws-modules/terraform-aws-vpc/pull/162 all credit goes to them for this wonderful example

* From copy and paste accidentally used variable name that differed from these variables

* Resolve typo in secondary_cidr_blocks

* Fixed README formatting

* Followups for #161

* Added local.vpc_id with description

README.md

@@ -221,6 +221,7 @@ Terraform version 0.10.3 or newer is required for this module to work.
 | redshift_subnet_tags | Additional tags for the redshift subnets | string | `<map>` | no |
 | redshift_subnets | A list of redshift subnets | list | `<list>` | no |
 | reuse_nat_ips | Should be true if you don't want EIPs to be created for your NAT Gateways and will instead pass them in via the 'external_nat_ip_ids' variable | string | `false` | no |
+| secondary_cidr_blocks | List of secondary CIDR blocks to associate with the VPC to extend the IP Address pool | string | `<list>` | no |
 | single_nat_gateway | Should be true if you want to provision a single shared NAT Gateway across all of your private networks | string | `false` | no |
 | tags | A map of tags to add to all resources | string | `<map>` | no |
 | vpc_tags | Additional tags for the VPC | string | `<map>` | no |
@@ -280,6 +281,7 @@ Terraform version 0.10.3 or newer is required for this module to work.
 | vpc_id | VPC |
 | vpc_instance_tenancy | Tenancy of instances spin up within VPC |
 | vpc_main_route_table_id | The ID of the main route table associated with this VPC |
+| vpc_secondary_cidr_blocks | List of secondary CIDR blocks of the VPC |
 
 <!-- END OF PRE-COMMIT-TERRAFORM DOCS HOOK -->
 

examples/secondary-cidr-blocks/README.md

+# Simple VPC with secondary CIDR blocks
+
+Configuration in this directory creates set of VPC resources across multiple CIDR blocks.
+
+There is a public and private subnet created per availability zone in addition to single NAT Gateway shared between all 3 availability zones.
+
+## Usage
+
+To run this example you need to execute:
+
+```bash
+$ terraform init
+$ terraform plan
+$ terraform apply
+```
+
+Note that this example may create resources which can cost money (AWS Elastic IP, for example). Run `terraform destroy` when you don't need these resources.
+
+<!-- BEGINNING OF PRE-COMMIT-TERRAFORM DOCS HOOK -->
+
+## Outputs
+
+| Name | Description |
+|------|-------------|
+| nat_public_ips | NAT gateways |
+| private_subnets | Subnets |
+| public_subnets | List of IDs of public subnets |
+| vpc_cidr_block | CIDR blocks |
+| vpc_id | VPC |
+| vpc_secondary_cidr_blocks | List of secondary CIDR blocks of the VPC |
+
+ <!-- END OF PRE-COMMIT-TERRAFORM DOCS HOOK -->

examples/secondary-cidr-blocks/main.tf

+provider "aws" {
+  region = "eu-west-1"
+}
+
+module "vpc" {
+  source = "../../"
+
+  name = "secondary-cidr-blocks-example"
+
+  cidr                  = "10.0.0.0/16"
+  secondary_cidr_blocks = ["10.1.0.0/16", "10.2.0.0/16"]
+
+  azs             = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
+  private_subnets = ["10.0.1.0/24", "10.1.2.0/24", "10.2.3.0/24"]
+  public_subnets  = ["10.0.101.0/24", "10.1.102.0/24", "10.2.103.0/24"]
+
+  assign_generated_ipv6_cidr_block = true
+  enable_nat_gateway               = true
+  single_nat_gateway               = true
+
+  public_subnet_tags = {
+    Name = "overridden-name-public"
+  }
+
+  tags = {
+    Owner       = "user"
+    Environment = "dev"
+  }
+
+  vpc_tags = {
+    Name = "vpc-name"
+  }
+}

examples/secondary-cidr-blocks/outputs.tf

+# VPC
+output "vpc_id" {
+  description = "The ID of the VPC"
+  value       = "${module.vpc.vpc_id}"
+}
+
+# CIDR blocks
+output "vpc_cidr_block" {
+  description = "The CIDR block of the VPC"
+  value       = ["${module.vpc.vpc_cidr_block}"]
+}
+
+output "vpc_secondary_cidr_blocks" {
+  description = "List of secondary CIDR blocks of the VPC"
+  value       = ["${module.vpc.vpc_secondary_cidr_blocks}"]
+}
+
+# Subnets
+output "private_subnets" {
+  description = "List of IDs of private subnets"
+  value       = ["${module.vpc.private_subnets}"]
+}
+
+output "public_subnets" {
+  description = "List of IDs of public subnets"
+  value       = ["${module.vpc.public_subnets}"]
+}
+
+# NAT gateways
+output "nat_public_ips" {
+  description = "List of public Elastic IPs created for AWS NAT Gateway"
+  value       = ["${module.vpc.nat_public_ips}"]
+}

main.tf

@@ -5,6 +5,9 @@ terraform {
 locals {
   max_subnet_length = "${max(length(var.private_subnets), length(var.elasticache_subnets), length(var.database_subnets), length(var.redshift_subnets))}"
   nat_gateway_count = "${var.single_nat_gateway ? 1 : (var.one_nat_gateway_per_az ? length(var.azs) : local.max_subnet_length)}"
+
+  # Use `local.vpc_id` to give a hint to Terraform that subnets should be deleted before secondary CIDR blocks can be free!
+  vpc_id = "${element(concat(aws_vpc_ipv4_cidr_block_association.this.*.vpc_id, aws_vpc.this.*.id, list("")), 0)}"
 }
 
 ######
@@ -22,6 +25,14 @@ resource "aws_vpc" "this" {
   tags = "${merge(map("Name", format("%s", var.name)), var.vpc_tags, var.tags)}"
 }
 
+resource "aws_vpc_ipv4_cidr_block_association" "this" {
+  count = "${var.create_vpc && length(var.secondary_cidr_blocks) > 0 ? length(var.secondary_cidr_blocks) : 0}"
+
+  vpc_id = "${aws_vpc.this.id}"
+
+  cidr_block = "${element(var.secondary_cidr_blocks, count.index)}"
+}
+
 ###################
 # DHCP Options Set
 ###################
@@ -43,7 +54,7 @@ resource "aws_vpc_dhcp_options" "this" {
 resource "aws_vpc_dhcp_options_association" "this" {
   count = "${var.create_vpc && var.enable_dhcp_options ? 1 : 0}"
 
-  vpc_id          = "${aws_vpc.this.id}"
+  vpc_id          = "${local.vpc_id}"
   dhcp_options_id = "${aws_vpc_dhcp_options.this.id}"
 }
 
@@ -53,7 +64,7 @@ resource "aws_vpc_dhcp_options_association" "this" {
 resource "aws_internet_gateway" "this" {
   count = "${var.create_vpc && length(var.public_subnets) > 0 ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(map("Name", format("%s", var.name)), var.igw_tags, var.tags)}"
 }
@@ -64,7 +75,7 @@ resource "aws_internet_gateway" "this" {
 resource "aws_route_table" "public" {
   count = "${var.create_vpc && length(var.public_subnets) > 0 ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(map("Name", format("%s-public", var.name)), var.public_route_table_tags, var.tags)}"
 }
@@ -88,7 +99,7 @@ resource "aws_route" "public_internet_gateway" {
 resource "aws_route_table" "private" {
   count = "${var.create_vpc && local.max_subnet_length > 0 ? local.nat_gateway_count : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(map("Name", (var.single_nat_gateway ? "${var.name}-private" : format("%s-private-%s", var.name, element(var.azs, count.index)))), var.private_route_table_tags, var.tags)}"
 
@@ -105,7 +116,7 @@ resource "aws_route_table" "private" {
 resource "aws_route_table" "database" {
   count = "${var.create_vpc && var.create_database_subnet_route_table && length(var.database_subnets) > 0 ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(var.tags, var.database_route_table_tags, map("Name", "${var.name}-database"))}"
 }
@@ -116,7 +127,7 @@ resource "aws_route_table" "database" {
 resource "aws_route_table" "redshift" {
   count = "${var.create_vpc && var.create_redshift_subnet_route_table && length(var.redshift_subnets) > 0 ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(var.tags, var.redshift_route_table_tags, map("Name", "${var.name}-redshift"))}"
 }
@@ -127,7 +138,7 @@ resource "aws_route_table" "redshift" {
 resource "aws_route_table" "elasticache" {
   count = "${var.create_vpc && var.create_elasticache_subnet_route_table && length(var.elasticache_subnets) > 0 ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(var.tags, var.elasticache_route_table_tags, map("Name", "${var.name}-elasticache"))}"
 }
@@ -138,7 +149,7 @@ resource "aws_route_table" "elasticache" {
 resource "aws_route_table" "intra" {
   count = "${var.create_vpc && length(var.intra_subnets) > 0 ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(map("Name", "${var.name}-intra"), var.intra_route_table_tags, var.tags)}"
 }
@@ -149,7 +160,7 @@ resource "aws_route_table" "intra" {
 resource "aws_subnet" "public" {
   count = "${var.create_vpc && length(var.public_subnets) > 0 && (!var.one_nat_gateway_per_az || length(var.public_subnets) >= length(var.azs)) ? length(var.public_subnets) : 0}"
 
-  vpc_id                  = "${aws_vpc.this.id}"
+  vpc_id                  = "${local.vpc_id}"
   cidr_block              = "${var.public_subnets[count.index]}"
   availability_zone       = "${element(var.azs, count.index)}"
   map_public_ip_on_launch = "${var.map_public_ip_on_launch}"
@@ -163,7 +174,7 @@ resource "aws_subnet" "public" {
 resource "aws_subnet" "private" {
   count = "${var.create_vpc && length(var.private_subnets) > 0 ? length(var.private_subnets) : 0}"
 
-  vpc_id            = "${aws_vpc.this.id}"
+  vpc_id            = "${local.vpc_id}"
   cidr_block        = "${var.private_subnets[count.index]}"
   availability_zone = "${element(var.azs, count.index)}"
 
@@ -176,7 +187,7 @@ resource "aws_subnet" "private" {
 resource "aws_subnet" "database" {
   count = "${var.create_vpc && length(var.database_subnets) > 0 ? length(var.database_subnets) : 0}"
 
-  vpc_id            = "${aws_vpc.this.id}"
+  vpc_id            = "${local.vpc_id}"
   cidr_block        = "${var.database_subnets[count.index]}"
   availability_zone = "${element(var.azs, count.index)}"
 
@@ -199,7 +210,7 @@ resource "aws_db_subnet_group" "database" {
 resource "aws_subnet" "redshift" {
   count = "${var.create_vpc && length(var.redshift_subnets) > 0 ? length(var.redshift_subnets) : 0}"
 
-  vpc_id            = "${aws_vpc.this.id}"
+  vpc_id            = "${local.vpc_id}"
   cidr_block        = "${var.redshift_subnets[count.index]}"
   availability_zone = "${element(var.azs, count.index)}"
 
@@ -222,7 +233,7 @@ resource "aws_redshift_subnet_group" "redshift" {
 resource "aws_subnet" "elasticache" {
   count = "${var.create_vpc && length(var.elasticache_subnets) > 0 ? length(var.elasticache_subnets) : 0}"
 
-  vpc_id            = "${aws_vpc.this.id}"
+  vpc_id            = "${local.vpc_id}"
   cidr_block        = "${var.elasticache_subnets[count.index]}"
   availability_zone = "${element(var.azs, count.index)}"
 
@@ -243,7 +254,7 @@ resource "aws_elasticache_subnet_group" "elasticache" {
 resource "aws_subnet" "intra" {
   count = "${var.create_vpc && length(var.intra_subnets) > 0 ? length(var.intra_subnets) : 0}"
 
-  vpc_id            = "${aws_vpc.this.id}"
+  vpc_id            = "${local.vpc_id}"
   cidr_block        = "${var.intra_subnets[count.index]}"
   availability_zone = "${element(var.azs, count.index)}"
 
@@ -308,7 +319,7 @@ data "aws_vpc_endpoint_service" "s3" {
 resource "aws_vpc_endpoint" "s3" {
   count = "${var.create_vpc && var.enable_s3_endpoint ? 1 : 0}"
 
-  vpc_id       = "${aws_vpc.this.id}"
+  vpc_id       = "${local.vpc_id}"
   service_name = "${data.aws_vpc_endpoint_service.s3.service_name}"
 }
 
@@ -345,7 +356,7 @@ data "aws_vpc_endpoint_service" "dynamodb" {
 resource "aws_vpc_endpoint" "dynamodb" {
   count = "${var.create_vpc && var.enable_dynamodb_endpoint ? 1 : 0}"
 
-  vpc_id       = "${aws_vpc.this.id}"
+  vpc_id       = "${local.vpc_id}"
   service_name = "${data.aws_vpc_endpoint_service.dynamodb.service_name}"
 }
 
@@ -421,7 +432,7 @@ resource "aws_route_table_association" "public" {
 resource "aws_vpn_gateway" "this" {
   count = "${var.create_vpc && var.enable_vpn_gateway ? 1 : 0}"
 
-  vpc_id = "${aws_vpc.this.id}"
+  vpc_id = "${local.vpc_id}"
 
   tags = "${merge(map("Name", format("%s", var.name)), var.vpn_gateway_tags, var.tags)}"
 }
@@ -429,7 +440,7 @@ resource "aws_vpn_gateway" "this" {
 resource "aws_vpn_gateway_attachment" "this" {
   count = "${var.vpn_gateway_id != "" ? 1 : 0}"
 
-  vpc_id         = "${aws_vpc.this.id}"
+  vpc_id         = "${local.vpc_id}"
   vpn_gateway_id = "${var.vpn_gateway_id}"
 }
 

outputs.tf

@@ -59,6 +59,11 @@ output "vpc_main_route_table_id" {
 //  value       = "${element(concat(aws_vpc.this.*.ipv6_cidr_block, list("")), 0)}"
 //}
 
+output "vpc_secondary_cidr_blocks" {
+  description = "List of secondary CIDR blocks of the VPC"
+  value       = ["${aws_vpc_ipv4_cidr_block_association.this.*.cidr_block}"]
+}
+
 # Subnets
 output "private_subnets" {
   description = "List of IDs of private subnets"

variables.tf

@@ -18,6 +18,11 @@ variable "assign_generated_ipv6_cidr_block" {
   default     = false
 }
 
+variable "secondary_cidr_blocks" {
+  description = "List of secondary CIDR blocks to associate with the VPC to extend the IP Address pool"
+  default     = []
+}
+
 variable "instance_tenancy" {
   description = "A tenancy option for instances launched into the VPC"
   default     = "default"