terraform-aws-multi-az-subnets

Terraform module for multi-AZ subnets provisioning.

The module creates private and public subnets in the provided Availability Zones.

The public subnets are routed to the Internet Gateway specified by var.igw_id.

nat_gateway_enabled flag controls the creation of NAT Gateways in the public subnets.

The private subnets are routed to the NAT Gateways provided in the var.az_ngw_ids map.

This project is part of our comprehensive "SweetOps" approach towards DevOps.

It's 100% Open Source and licensed under the APACHE2.

Screenshots

Example of terraform apply outputs

Usage

module "vpc" {
  source     = "git::https://github.com/cloudposse/terraform-aws-vpc.git?ref=master"
  namespace  = "${var.namespace}"
  name       = "vpc"
  stage      = "${var.stage}"
  cidr_block = "${var.cidr_block}"
}

locals {
  public_cidr_block  = "${cidrsubnet(module.vpc.vpc_cidr_block, 1, 0)}"
  private_cidr_block = "${cidrsubnet(module.vpc.vpc_cidr_block, 1, 1)}"
}

module "public_subnets" {
  source              = "git::https://github.com/cloudposse/terraform-aws-multi-az-subnets.git?ref=master"
  namespace           = "${var.namespace}"
  stage               = "${var.stage}"
  name                = "${var.name}"
  availability_zones  = ["us-east-1a", "us-east-1b", "us-east-1c"]
  vpc_id              = "${module.vpc.vpc_id}"
  cidr_block          = "${local.public_cidr_block}"
  type                = "public"
  igw_id              = "${module.vpc.igw_id}"
  nat_gateway_enabled = "true"
}

module "private_subnets" {
  source              = "git::https://github.com/cloudposse/terraform-aws-multi-az-subnets.git?ref=master"
  namespace           = "${var.namespace}"
  stage               = "${var.stage}"
  name                = "${var.name}"
  availability_zones  = ["us-east-1a", "us-east-1b", "us-east-1c"]
  vpc_id              = "${module.vpc.vpc_id}"
  cidr_block          = "${local.private_cidr_block}"
  type                = "private"

  # Map of AZ names to NAT Gateway IDs that was created in "public_subnets" module
  az_ngw_ids          = "${module.public_subnets.az_ngw_ids}"

  # Need to explicitly provide the count since Terraform currently can't use dynamic count on computed resources from different modules
  # https://github.com/hashicorp/terraform/issues/10857
  # https://github.com/hashicorp/terraform/issues/12125
  # https://github.com/hashicorp/terraform/issues/4149
  az_ngw_count = 3
}

Examples

Given the following configuration

module "vpc" {
  source     = "git::https://github.com/cloudposse/terraform-aws-vpc.git?ref=master"
  namespace  = "${var.namespace}"
  name       = "vpc"
  stage      = "${var.stage}"
  cidr_block = "${var.cidr_block}"
}

locals {
  public_cidr_block  = "${cidrsubnet(module.vpc.vpc_cidr_block, 1, 0)}"
  private_cidr_block = "${cidrsubnet(module.vpc.vpc_cidr_block, 1, 1)}"
}

module "public_subnets" {
  source              = "git::https://github.com/cloudposse/terraform-aws-multi-az-subnets.git?ref=master"
  namespace           = "${var.namespace}"
  stage               = "${var.stage}"
  name                = "${var.name}"
  availability_zones  = ["us-east-1a", "us-east-1b", "us-east-1c"]
  vpc_id              = "${module.vpc.vpc_id}"
  cidr_block          = "${local.public_cidr_block}"
  type                = "public"
  igw_id              = "${module.vpc.igw_id}"
  nat_gateway_enabled = "true"
}

module "private_subnets" {
  source              = "git::https://github.com/cloudposse/terraform-aws-multi-az-subnets.git?ref=master"
  namespace           = "${var.namespace}"
  stage               = "${var.stage}"
  name                = "${var.name}"
  availability_zones  = ["us-east-1a", "us-east-1b", "us-east-1c"]
  vpc_id              = "${module.vpc.vpc_id}"
  cidr_block          = "${local.private_cidr_block}"
  type                = "private"
  az_ngw_ids          = "${module.public_subnets.az_ngw_ids}"
  az_ngw_count        = 3
}

output "private_az_subnet_ids" {
  value = "${module.private_subnets.az_subnet_ids}"
}

output "public_az_subnet_ids" {
  value = "${module.public_subnets.az_subnet_ids}"
}

the output Maps of AZ names to subnet IDs look like these

public_az_subnet_ids = {
  us-east-1a = subnet-ea58d78e
  us-east-1b = subnet-556ee131
  us-east-1c = subnet-6f54db0b
}
private_az_subnet_ids = {
  us-east-1a = subnet-376de253
  us-east-1b = subnet-9e53dcfa
  us-east-1c = subnet-a86fe0cc
}

and the created subnet IDs could be found by the AZ names using map["key"] or lookup(map, key, [default]),

for example:

public_az_subnet_ids["us-east-1a"]

lookup(private_az_subnet_ids, "us-east-1b")

Makefile Targets

Available targets:

  help                                Help screen
  help/all                            Display help for all targets
  help/short                          This help short screen
  lint                                Lint terraform code

Inputs

Name	Description	Type	Default	Required
attributes	Additional attributes (e.g. `policy` or `role`)	list	`<list>`	no
availability_zones	List of Availability Zones (e.g. `['us-east-1a', 'us-east-1b', 'us-east-1c']`)	list	`<list>`	no
az_ngw_count	Count of items in the `az_ngw_ids` map. Needs to be explicitly provided since Terraform currently can't use dynamic count on computed resources from different modules. hashicorp/terraform#10857	string	`0`	no
az_ngw_ids	Only for private subnets. Map of AZ names to NAT Gateway IDs that are used as default routes when creating private subnets	map	`<map>`	no
cidr_block	Base CIDR block which is divided into subnet CIDR blocks (e.g. `10.0.0.0/16`)	string	-	yes
delimiter	Delimiter to be used between `namespace`, `stage`, `name` and `attributes`	string	`-`	no
enabled	Set to false to prevent the module from creating any resources	string	`true`	no
igw_id	Internet Gateway ID that is used as a default route when creating public subnets (e.g. `igw-9c26a123`)	string	``	no
max_subnets	Maximum number of subnets that can be created. The variable is used for CIDR blocks calculation	string	`6`	no
name	Application or solution name	string	-	yes
namespace	Namespace (e.g. `cp` or `cloudposse`)	string	-	yes
nat_gateway_enabled	Flag to enable/disable NAT Gateways creation in public subnets	string	`true`	no
private_network_acl_egress	Egress network ACL rules	list	`<list>`	no
private_network_acl_id	Network ACL ID that is added to the private subnets. If empty, a new ACL will be created	string	``	no
private_network_acl_ingress	Egress network ACL rules	list	`<list>`	no
public_network_acl_egress	Egress network ACL rules	list	`<list>`	no
public_network_acl_id	Network ACL ID that is added to the public subnets. If empty, a new ACL will be created	string	``	no
public_network_acl_ingress	Egress network ACL rules	list	`<list>`	no
stage	Stage (e.g. `prod`, `dev`, `staging`)	string	-	yes
tags	Additional tags (e.g. map(`BusinessUnit`,`XYZ`)	map	`<map>`	no
type	Type of subnets to create (`private` or `public`)	string	`private`	no
vpc_id	VPC ID	string	-	yes

Outputs

Name	Description
az_ngw_ids	Map of AZ names to NAT Gateway IDs (only for public subnets)
az_route_table_ids	Map of AZ names to Route Table IDs
az_subnet_arns	Map of AZ names to subnet ARNs
az_subnet_ids	Map of AZ names to subnet IDs

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Related Projects

Check out these related projects.

terraform-aws-named-subnets - Terraform module for named subnets provisioning.
terraform-aws-dynamic-subnets - Terraform module for public and private subnets provisioning in existing VPC
terraform-aws-vpc - Terraform Module that defines a VPC with public/private subnets across multiple AZs with Internet Gateways
terraform-aws-cloudwatch-flow-logs - Terraform module for enabling flow logs for vpc and subnets.

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Licensed to the Apache Software Foundation (ASF) under one
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Contributors

Andriy Knysh

cameroncooper/terraform-aws-multi-az-subnets