terraform-aws-transit-gateway

Terraform module to provision:

AWS Transit Gateway
AWS Resource Access Manager (AWS RAM) Resource Share to share the Transit Gateway with the Organization or another AWS Account (configurable via the variables ram_resource_share_enabled and ram_principal)
Transit Gateway route table
Transit Gateway VPC attachments to connect multiple VPCs via the Transit Gateway
Transit Gateway route table propagations to create propagated routes and allow traffic from the Transit Gateway to the VPC attachments
Transit Gateway route table associations to allow traffic from the VPC attachments to the Transit Gateway
Transit Gateway static routes (static routes have a higher precedence than propagated routes)
Subnet routes to route traffic from the subnets in each VPC to the other Transit Gateway VPC attachments

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Introduction

This module is configurable via the variable transit_gateway_config - see usage and examples below.

The variable transit_gateway_config is a map of environment names (e.g. prod, staging, dev) to the environment configurations.

Each environment configuration contains the following fields:

vpc_id - The ID of the VPC for which to create a VPC attachment and route table associations and propagations.
vpc_cidr - VPC CIDR block.
subnet_ids - The IDs of the subnets in the VPC.
static_routes - A list of Transit Gateway static route configurations. Note that static routes have a higher precedence than propagated routes.
subnet_route_table_ids - The IDs of the subnet route tables. The route tables are used to add routes to allow traffix from the subnets in one VPC to the other VPC attachments.
route_to - A set of environment names to route traffic from the current environment to the specified environments. In the example below, in the prod environment we create subnet routes to route traffic from the prod subnets to the VPC attachments in the staging and dev environments. Specify either route_to or route_to_cidr_blocks. route_to_cidr_blocks supersedes route_to.
route_to_cidr_blocks - A set of VPC CIDR blocks to route traffic from the current environment to the specified VPC CIDR blocks. In the example below, in the staging environment we create subnet routes to route traffic from the staging subnets to the dev VPC CIDR. Specify either route_to or route_to_cidr_blocks. route_to_cidr_blocks supersedes route_to.
transit_gateway_vpc_attachment_id - An existing Transit Gateway Attachment ID. If provided, the module will use it instead of creating a new one.

You now have the option to have Terraform manage route table entries by key, whereas previously they were only managed by index. The advantage of managing them by key is that if a route table ID or destination CIDR changes, only that entry is affected, whereas when managed by index, all the entries after the first affected index may be destroyed and re-created at a different index. The reason this is left as an option, with the default being to manage the entries by index, is that if you are creating the VPC or subnets at the same time you are creating the Transit Gateway, then Terraform will not be able to generate the keys during the plan phase and the plan will fail with the error The "for_each" value depends on resource attributes that cannot be determined until apply.... We recommend setting route_keys_enabled to true unless you get this error, in which case you must leave it set to its default value of false.

NOTE: This module requires Terraform 0.13 and newer since it uses module expansion with for_each.

Security & Compliance

Security scanning is graciously provided by Bridgecrew. Bridgecrew is the leading fully hosted, cloud-native solution providing continuous Terraform security and compliance.

Benchmark	Description
	Infrastructure Security Compliance
	Center for Internet Security, KUBERNETES Compliance
	Center for Internet Security, AWS Compliance
	Center for Internet Security, AZURE Compliance
	Payment Card Industry Data Security Standards Compliance
	National Institute of Standards and Technology Compliance
	Information Security Management System, ISO/IEC 27001 Compliance
	Service Organization Control 2 Compliance
	Center for Internet Security, GCP Compliance
	Health Insurance Portability and Accountability Compliance

Usage

IMPORTANT: We do not pin modules to versions in our examples because of the difficulty of keeping the versions in the documentation in sync with the latest released versions. We highly recommend that in your code you pin the version to the exact version you are using so that your infrastructure remains stable, and update versions in a systematic way so that they do not catch you by surprise.

Also, because of a bug in the Terraform registry (hashicorp/terraform#21417), the registry shows many of our inputs as required when in fact they are optional. The table below correctly indicates which inputs are required.

Here's how to invoke this module in your projects:

locals {
  transit_gateway_config = {
    prod = {
      vpc_id                            = module.vpc_prod.vpc_id
      vpc_cidr                          = module.vpc_prod.vpc_cidr_block
      subnet_ids                        = module.subnets_prod.private_subnet_ids
      subnet_route_table_ids            = module.subnets_prod.private_route_table_ids
      route_to                          = ["staging", "dev"]
      route_to_cidr_blocks              = null
      transit_gateway_vpc_attachment_id = null

      static_routes = [
        {
          blackhole              = true
          destination_cidr_block = "0.0.0.0/0"
        },
        {
          blackhole              = false
          destination_cidr_block = "172.16.1.0/24"
        }
      ]
    },

    staging = {
      vpc_id                            = module.vpc_staging.vpc_id
      vpc_cidr                          = module.vpc_staging.vpc_cidr_block
      subnet_ids                        = module.subnets_staging.private_subnet_ids
      subnet_route_table_ids            = module.subnets_staging.private_route_table_ids
      route_to                          = null
      route_to_cidr_blocks              = [module.vpc_dev.vpc_cidr_block]
      transit_gateway_vpc_attachment_id = null

      static_routes = [
        {
          blackhole              = false
          destination_cidr_block = "172.32.1.0/24"
        }
      ]
    },

    dev = {
      vpc_id                            = module.vpc_dev.vpc_id
      vpc_cidr                          = module.vpc_dev.vpc_cidr_block
      subnet_ids                        = module.subnets_dev.private_subnet_ids
      subnet_route_table_ids            = module.subnets_dev.private_route_table_ids
      route_to                          = null
      route_to_cidr_blocks              = null
      transit_gateway_vpc_attachment_id = null
      static_routes                     = null
    }
  }
}

module "transit_gateway" {
  source = "cloudposse/transit-gateway/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"

  ram_resource_share_enabled = false
  config                     = local.transit_gateway_config

  context = module.this.context
}

Examples

Here is a working example of using this module:

examples/complete

Here are automated tests for the complete example using bats and Terratest (which tests and deploys the example on AWS):

test

Here is an example of using this module in a multi-account environment (with the Transit Gateway in one AWS account and all the VPC attachments and routes in different AWS accounts):

examples/multi-account

Makefile Targets

Available targets:

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

Requirements

Name	Version
terraform	>= 0.13.0
aws	>= 3.0
local	>= 1.2
random	>= 2.2

Providers

Name	Version
aws	>= 3.0

Inputs

Name	Description	Type	Default	Required
additional_tag_map	Additional tags for appending to tags_as_list_of_maps. Not added to `tags`.	`map(string)`	`{}`	no
allow_external_principals	Indicates whether principals outside your organization can be associated with a resource share	`bool`	`false`	no
attributes	Additional attributes (e.g. `1`)	`list(string)`	`[]`	no
auto_accept_shared_attachments	Whether resource attachment requests are automatically accepted. Valid values: `disable`, `enable`. Default value: `disable`	`string`	`"enable"`	no
config	Configuration for VPC attachments, Transit Gateway routes, and subnet routes	map(object({ vpc_id = string vpc_cidr = string subnet_ids = set(string) subnet_route_table_ids = set(string) route_to = set(string) route_to_cidr_blocks = set(string) transit_gateway_vpc_attachment_id = string static_routes = set(object({ blackhole = bool destination_cidr_block = string })) }))	`null`	no
context	Single object for setting entire context at once. See description of individual variables for details. Leave string and numeric variables as `null` to use default value. Individual variable settings (non-null) override settings in context object, except for attributes, tags, and additional_tag_map, which are merged.	`any`	{ "additional_tag_map": {}, "attributes": [], "delimiter": null, "enabled": true, "environment": null, "id_length_limit": null, "label_key_case": null, "label_order": [], "label_value_case": null, "name": null, "namespace": null, "regex_replace_chars": null, "stage": null, "tags": {} }	no
create_transit_gateway	Whether to create a Transit Gateway. If set to `false`, an existing Transit Gateway ID must be provided in the variable `existing_transit_gateway_id`	`bool`	`true`	no
create_transit_gateway_route_table	Whether to create a Transit Gateway Route Table. If set to `false`, an existing Transit Gateway Route Table ID must be provided in the variable `existing_transit_gateway_route_table_id`	`bool`	`true`	no
create_transit_gateway_route_table_association_and_propagation	Whether to create Transit Gateway Route Table associations and propagations	`bool`	`true`	no
create_transit_gateway_vpc_attachment	Whether to create Transit Gateway VPC Attachments	`bool`	`true`	no
default_route_table_association	Whether resource attachments are automatically associated with the default association route table. Valid values: `disable`, `enable`. Default value: `enable`	`string`	`"disable"`	no
default_route_table_propagation	Whether resource attachments automatically propagate routes to the default propagation route table. Valid values: `disable`, `enable`. Default value: `enable`	`string`	`"disable"`	no
delimiter	Delimiter to be used between `namespace`, `environment`, `stage`, `name` and `attributes`. Defaults to `-` (hyphen). Set to `""` to use no delimiter at all.	`string`	`null`	no
dns_support	Whether resource attachments automatically propagate routes to the default propagation route table. Valid values: `disable`, `enable`. Default value: `enable`	`string`	`"enable"`	no
enabled	Set to false to prevent the module from creating any resources	`bool`	`null`	no
environment	Environment, e.g. 'uw2', 'us-west-2', OR 'prod', 'staging', 'dev', 'UAT'	`string`	`null`	no
existing_transit_gateway_id	Existing Transit Gateway ID. If provided, the module will not create a Transit Gateway but instead will use the existing one	`string`	`null`	no
existing_transit_gateway_route_table_id	Existing Transit Gateway Route Table ID. If provided, the module will not create a Transit Gateway Route Table but instead will use the existing one	`string`	`null`	no
id_length_limit	Limit `id` to this many characters (minimum 6). Set to `0` for unlimited length. Set to `null` for default, which is `0`. Does not affect `id_full`.	`number`	`null`	no
label_key_case	The letter case of label keys (`tag` names) (i.e. `name`, `namespace`, `environment`, `stage`, `attributes`) to use in `tags`. Possible values: `lower`, `title`, `upper`. Default value: `title`.	`string`	`null`	no
label_order	The naming order of the id output and Name tag. Defaults to ["namespace", "environment", "stage", "name", "attributes"]. You can omit any of the 5 elements, but at least one must be present.	`list(string)`	`null`	no
label_value_case	The letter case of output label values (also used in `tags` and `id`). Possible values: `lower`, `title`, `upper` and `none` (no transformation). Default value: `lower`.	`string`	`null`	no
name	Solution name, e.g. 'app' or 'jenkins'	`string`	`null`	no
namespace	Namespace, which could be your organization name or abbreviation, e.g. 'eg' or 'cp'	`string`	`null`	no
ram_principal	The principal to associate with the resource share. Possible values are an AWS account ID, an Organization ARN, or an Organization Unit ARN. If this is not provided and `ram_resource_share_enabled` is set to `true`, the Organization ARN will be used	`string`	`null`	no
ram_resource_share_enabled	Whether to enable sharing the Transit Gateway with the Organization using Resource Access Manager (RAM)	`bool`	`false`	no
regex_replace_chars	Regex to replace chars with empty string in `namespace`, `environment`, `stage` and `name`. If not set, `"/[^a-zA-Z0-9-]/"` is used to remove all characters other than hyphens, letters and digits.	`string`	`null`	no
route_keys_enabled	If true, Terraform will use keys to label routes, preventing unnecessary changes, but this requires that the VPCs and subnets already exist before using this module. If false, Terraform will use numbers to label routes, and a single change may cascade to a long list of changes because the index or order has changed, but this will work when the `true` setting generates the error `The "for_each" value depends on resource attributes...`	`bool`	`false`	no
stage	Stage, e.g. 'prod', 'staging', 'dev', OR 'source', 'build', 'test', 'deploy', 'release'	`string`	`null`	no
tags	Additional tags (e.g. `map('BusinessUnit','XYZ')`	`map(string)`	`{}`	no
vpc_attachment_dns_support	Whether resource attachments automatically propagate routes to the default propagation route table. Valid values: `disable`, `enable`. Default value: `enable`	`string`	`"enable"`	no
vpc_attachment_ipv6_support	Whether resource attachments automatically propagate routes to the default propagation route table. Valid values: `disable`, `enable`. Default value: `enable`	`string`	`"disable"`	no
vpn_ecmp_support	Whether resource attachments automatically propagate routes to the default propagation route table. Valid values: `disable`, `enable`. Default value: `enable`	`string`	`"enable"`	no

Outputs

Name	Description
subnet_route_ids	Subnet route identifiers combined with destinations
transit_gateway_arn	Transit Gateway ARN
transit_gateway_association_default_route_table_id	Transit Gateway association default route table ID
transit_gateway_id	Transit Gateway ID
transit_gateway_propagation_default_route_table_id	Transit Gateway propagation default route table ID
transit_gateway_route_ids	Transit Gateway route identifiers combined with destinations
transit_gateway_route_table_id	Transit Gateway route table ID
transit_gateway_vpc_attachment_ids	Transit Gateway VPC attachment IDs

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Related Projects

Check out these related projects.

terraform-null-label - Terraform module designed to generate consistent names and tags for resources. Use terraform-null-label to implement a strict naming convention
terraform-aws-vpc - Terraform Module that defines a VPC with public/private subnets across multiple AZs with Internet Gateways
terraform-aws-vpc-peering - Terraform module to create a peering connection between two VPCs
terraform-aws-kops-vpc-peering - Terraform module to create a peering connection between a backing services VPC and a VPC created by Kops
terraform-aws-dynamic-subnets - Terraform module for public and private subnets provisioning in an existing VPC
terraform-aws-multi-az-subnets - Terraform module for multi-AZ public and private subnets provisioning
terraform-aws-named-subnets - Terraform module for named subnets provisioning

References

For additional context, refer to some of these links.

Terraform Standard Module Structure - HashiCorp's standard module structure is a file and directory layout we recommend for reusable modules distributed in separate repositories.
Terraform Module Requirements - HashiCorp's guidance on all the requirements for publishing a module. Meeting the requirements for publishing a module is extremely easy.
Terraform random_integer Resource - The resource random_integer generates random values from a given range, described by the min and max attributes of a given resource.
Terraform Version Pinning - The required_version setting can be used to constrain which versions of the Terraform CLI can be used with your configuration

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Copyrights

License

See LICENSE for full details.

Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
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Contributors

Erik Osterman	Andriy Knysh

Name		Name	Last commit message	Last commit date
Latest commit History 8 Commits
.github		.github
docs		docs
examples		examples
modules		modules
test		test
.editorconfig		.editorconfig
.gitignore		.gitignore
LICENSE		LICENSE
Makefile		Makefile
README.md		README.md
README.yaml		README.yaml
context.tf		context.tf
main.tf		main.tf
outputs.tf		outputs.tf
ram.tf		ram.tf
variables.tf		variables.tf
versions.tf		versions.tf

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