Module: named-subnets

Terraform module for named subnets provisioning.

Usage

Simple example, with private and public subnets in one Availability Zone:

module "vpc" {
  source = "cloudposse/vpc/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace  = "eg"
  name       = "vpc"
  stage      = "dev"
  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 = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["web1", "web2", "web3"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.public_cidr_block
  type              = "public"
  igw_id            = module.vpc.igw_id
  availability_zone = "us-east-1a"
}

module "private_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "database"
  subnet_names      = ["kafka", "cassandra", "zookeeper"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.private_cidr_block
  type              = "private"
  availability_zone = "us-east-1a"
  ngw_id            = module.public_subnets.ngw_id
}

Simple example, with ENI as default route gateway for private subnets

resource "aws_network_interface" "default" {
  subnet_id         = module.us_east_1b_public_subnets.subnet_ids[0]
  source_dest_check = false
  tags              = module.network_interface_label.id
}

module "us_east_1b_private_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["charlie", "echo", "bravo"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.us_east_1b_private_cidr_block
  type              = "private"
  availability_zone = "us-east-1b"
  eni_id            = aws_network_interface.default.id
  attributes        = ["us-east-1b"]
}

Full example, with private and public subnets in two Availability Zones for High Availability:

module "vpc" {
  source = "cloudposse/vpc/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace  = "eg"
  name       = "vpc"
  stage      = "dev"
  cidr_block = var.cidr_block
}

locals {
  us_east_1a_public_cidr_block  = cidrsubnet(module.vpc.vpc_cidr_block, 2, 0)
  us_east_1a_private_cidr_block = cidrsubnet(module.vpc.vpc_cidr_block, 2, 1)
  us_east_1b_public_cidr_block  = cidrsubnet(module.vpc.vpc_cidr_block, 2, 2)
  us_east_1b_private_cidr_block = cidrsubnet(module.vpc.vpc_cidr_block, 2, 3)
}

module "us_east_1a_public_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["apples", "oranges", "grapes"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.us_east_1a_public_cidr_block
  type              = "public"
  igw_id            = module.vpc.igw_id
  availability_zone = "us-east-1a"
  attributes        = ["us-east-1a"]
}

module "us_east_1a_private_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["charlie", "echo", "bravo"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.us_east_1a_private_cidr_block
  type              = "private"
  availability_zone = "us-east-1a"
  ngw_id            = module.us_east_1a_public_subnets.ngw_id
  attributes        = ["us-east-1a"]
}

module "us_east_1b_public_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["apples", "oranges", "grapes"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.us_east_1b_public_cidr_block
  type              = "public"
  igw_id            = module.vpc.igw_id
  availability_zone = "us-east-1b"
  attributes        = ["us-east-1b"]
}

module "us_east_1b_private_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["charlie", "echo", "bravo"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.us_east_1b_private_cidr_block
  type              = "private"
  availability_zone = "us-east-1b"
  ngw_id            = module.us_east_1b_public_subnets.ngw_id
  attributes        = ["us-east-1b"]
}

resource "aws_network_interface" "default" {
  subnet_id         = module.us_east_1b_public_subnets.subnet_ids[0]
  source_dest_check = false
  tags              = module.network_interface_label.id
}

module "us_east_1b_private_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["charlie", "echo", "bravo"]
  vpc_id            = module.vpc.vpc_id
  cidr_block        = local.us_east_1b_private_cidr_block
  type              = "private"
  availability_zone = "us-east-1b"
  eni_id            = aws_network_interface.default.id
  attributes        = ["us-east-1b"]
}

Caveat

You must use only one type of device for a default route gateway per route table. ENI or NGW

Given the following configuration (see the Simple example above)

locals {
  public_cidr_block  = cidrsubnet(var.vpc_cidr, 1, 0)
  private_cidr_block = cidrsubnet(var.vpc_cidr, 1, 1)
}

module "public_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "app"
  subnet_names      = ["web1", "web2", "web3"]
  vpc_id            = var.vpc_id
  cidr_block        = local.public_cidr_block
  type              = "public"
  availability_zone = "us-east-1a"
  igw_id            = var.igw_id
}

module "private_subnets" {
  source = "cloudposse/named-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"
  namespace         = "eg"
  stage             = "dev"
  name              = "database"
  subnet_names      = ["kafka", "cassandra", "zookeeper"]
  vpc_id            = var.vpc_id
  cidr_block        = local.private_cidr_block
  type              = "private"
  availability_zone = "us-east-1a"
  ngw_id            = module.public_subnets.ngw_id
}

output "private_named_subnet_ids" {
  value = module.private_subnets.named_subnet_ids
}

output "public_named_subnet_ids" {
  value = module.public_subnets.named_subnet_ids
}

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

public_named_subnet_ids = {
  web1 = subnet-ea58d78e
  web2 = subnet-556ee131
  web3 = subnet-6f54db0b
}
private_named_subnet_ids = {
  cassandra = subnet-376de253
  kafka = subnet-9e53dcfa
  zookeeper = subnet-a86fe0cc
}

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

for example:

public_named_subnet_ids["web1"]

lookup(private_named_subnet_ids, "kafka")