AWS VPC Terraform module

Terraform module which creates VPC resources on AWS.

These types of resources are supported:

• VPC
• Subnet
• Route
• Route table
• Internet Gateway
• NAT Gateway
• VPN Gateway
• VPC Endpoint (S3 and DynamoDB)
• RDS DB Subnet Group
• ElastiCache Subnet Group
• Redshift Subnet Group
• DHCP Options Set
• Default VPC

Usage

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  name = "my-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  enable_nat_gateway = true
  enable_vpn_gateway = true

  tags = {
    Terraform = "true"
    Environment = "dev"
  }
}

External NAT Gateway IPs

By default this module will provision new Elastic IPs for the VPC's NAT Gateways. This means that when creating a new VPC, new IPs are allocated, and when that VPC is destroyed those IPs are released. Sometimes it is handy to keep the same IPs even after the VPC is destroyed and re-created. To that end, it is possible to assign existing IPs to the NAT Gateways. This prevents the destruction of the VPC from releasing those IPs, while making it possible that a re-created VPC uses the same IPs.

To achieve this, allocate the IPs outside the VPC module declaration.

resource "aws_eip" "nat" {
  count = 3

  vpc = true
}

Then, pass the allocated IPs as a parameter to this module.

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  # The rest of arguments are omitted for brevity

  enable_nat_gateway  = true
  single_nat_gateway  = false
  reuse_nat_ips       = true                      # <= Skip creation of EIPs for the NAT Gateways
  external_nat_ip_ids = ["${aws_eip.nat.*.id}"]   # <= IPs specified here as input to the module
}

Note that in the example we allocate 3 IPs because we will be provisioning 3 NAT Gateways (due to single_nat_gateway = false and having 3 subnets). If, on the other hand, single_nat_gateway = true, then aws_eip.nat would only need to allocate 1 IP. Passing the IPs into the module is done by setting two variables reuse_nat_ips = true and external_nat_ip_ids = ["${aws_eip.nat.*.id}"].

NAT Gateway Scenarios

This module supports three scenarios for creating NAT gateways. Each will be explained in further detail in the corresponding sections.

• One NAT Gateway per subnet (default behavior)
  • enable_nat_gateway = true
  • single_nat_gateway = false
  • one_nat_gateway_per_az = false
• Single NAT Gateway
  • enable_nat_gateway = true
  • single_nat_gateway = true
  • one_nat_gateway_per_az = false
• One NAT Gateway per availability zone
  • enable_nat_gateway = true
  • single_nat_gateway = false
  • one_nat_gateway_per_az = true

If both single_nat_gateway and one_nat_gateway_per_az are set to true, then single_nat_gateway takes precedence.

One NAT Gateway per subnet (default)

By default, the module will determine the number of NAT Gateways to create based on the the max() of the private subnet lists (database_subnets, elasticache_subnets, private_subnets, and redshift_subnets). The module does not take into account the number of intra_subnets, since the latter are designed to have no Internet access via NAT Gateway. For example, if your configuration looks like the following:

database_subnets    = ["10.0.21.0/24", "10.0.22.0/24"]
elasticache_subnets = ["10.0.31.0/24", "10.0.32.0/24"]
private_subnets     = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24", "10.0.4.0/24", "10.0.5.0/24"]
redshift_subnets    = ["10.0.41.0/24", "10.0.42.0/24"]
intra_subnets       = ["10.0.51.0/24", "10.0.52.0/24", "10.0.53.0/24"]

Then 5 NAT Gateways will be created since 5 private subnet CIDR blocks were specified.

Single NAT Gateway

If single_nat_gateway = true, then all private subnets will route their Internet traffic through this single NAT gateway. The NAT gateway will be placed in the first public subnet in your public_subnets block.

One NAT Gateway per availability zone

If one_nat_gateway_per_az = true and single_nat_gateway = false, then the module will place one NAT gateway in each availability zone you specify in var.azs. There are some requirements around using this feature flag:

• The variable var.azs must be specified.
• The number of public subnet CIDR blocks specified in public_subnets must be greater than or equal to the number of availability zones specified in var.azs. This is to ensure that each NAT Gateway has a dedicated public subnet to deploy to.

Private Versus Intra Subnets

By default, if NAT Gateways are enabled, private subnets will be configured with routes for Internet traffic that point at the NAT Gateways configured by use of the above options. If you need private subnets that should have no Internet routing (in the sense of RFC1918 Category 1 subnets), intra_subnets are available. An example use case is configuration of Lambda functions within a VPC, where the Lambda functions only need to pass traffic to internal resources or VPC endpoints for AWS services. Since Lambda functions allocate Elastic Network Interfaces in proportion to the traffic received, it can be useful to allocate a large private subnet for such allocations, while keeping the traffic they generate entirely internal to the VPC. You can add additional tags with intra_subnet_tags as with other subnet types.

Conditional creation

Sometimes you need to have a way to create VPC resources conditionally but Terraform does not allow to use count inside module block, so the solution is to specify argument create_vpc.

# This VPC will not be created
module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  create_vpc = false
  # ... omitted
}

Terraform version

Terraform version 0.10.3 or newer is required for this module to work.

Examples

• Simple VPC
• Complete VPC
• Manage Default VPC
• Few tests and edge cases examples: #46, #44, #108

Inputs

Name	Description	Type	Default	Required
azs	A list of availability zones in the region	string	<list>	no
cidr	The CIDR block for the VPC. Default value is a valid CIDR, but not acceptable by AWS and should be overriden	string	0.0.0.0/0	no
create_database_subnet_group	Controls if database subnet group should be created	string	true	no
create_vpc	Controls if VPC should be created (it affects almost all resources)	string	true	no
database_subnet_tags	Additional tags for the database subnets	string	<map>	no
database_subnets	A list of database subnets	list	<list>	no
default_route_table_tags	Additional tags for the default route table	string	<map>	no
default_vpc_enable_classiclink	Should be true to enable ClassicLink in the Default VPC	string	false	no
default_vpc_enable_dns_hostnames	Should be true to enable DNS hostnames in the Default VPC	string	false	no
default_vpc_enable_dns_support	Should be true to enable DNS support in the Default VPC	string	true	no
default_vpc_name	Name to be used on the Default VPC	string	``	no
default_vpc_tags	Additional tags for the Default VPC	string	<map>	no
dhcp_options_domain_name	Specifies DNS name for DHCP options set	string	``	no
dhcp_options_domain_name_servers	Specify a list of DNS server addresses for DHCP options set, default to AWS provided	list	<list>	no
dhcp_options_netbios_name_servers	Specify a list of netbios servers for DHCP options set	list	<list>	no
dhcp_options_netbios_node_type	Specify netbios node_type for DHCP options set	string	``	no
dhcp_options_ntp_servers	Specify a list of NTP servers for DHCP options set	list	<list>	no
dhcp_options_tags	Additional tags for the DHCP option set	string	<map>	no
elasticache_subnet_tags	Additional tags for the elasticache subnets	string	<map>	no
elasticache_subnets	A list of elasticache subnets	list	<list>	no
enable_dhcp_options	Should be true if you want to specify a DHCP options set with a custom domain name, DNS servers, NTP servers, netbios servers, and/or netbios server type	string	false	no
enable_dns_hostnames	Should be true to enable DNS hostnames in the VPC	string	false	no
enable_dns_support	Should be true to enable DNS support in the VPC	string	true	no
enable_dynamodb_endpoint	Should be true if you want to provision a DynamoDB endpoint to the VPC	string	false	no
enable_nat_gateway	Should be true if you want to provision NAT Gateways for each of your private networks	string	false	no
enable_s3_endpoint	Should be true if you want to provision an S3 endpoint to the VPC	string	false	no
enable_vpn_gateway	Should be true if you want to create a new VPN Gateway resource and attach it to the VPC	string	false	no
external_nat_ip_ids	List of EIP IDs to be assigned to the NAT Gateways (used in combination with reuse_nat_ips)	list	<list>	no
instance_tenancy	A tenancy option for instances launched into the VPC	string	default	no
intra_subnet_tags	Additional tags for the intra subnets	string	<map>	no
intra_subnets	A list of intra subnets	list	<list>	no
manage_default_vpc	Should be true to adopt and manage Default VPC	string	false	no
map_public_ip_on_launch	Should be false if you do not want to auto-assign public IP on launch	string	true	no
name	Name to be used on all the resources as identifier	string	``	no
one_nat_gateway_per_az	Should be true if you want only one NAT Gateway per availability zone. Requires var.azs to be set, and the number of public_subnets created to be greater than or equal to the number of availability zones specified in var.azs.	string	false	no
private_route_table_tags	Additional tags for the private route tables	string	<map>	no
private_subnet_tags	Additional tags for the private subnets	string	<map>	no
private_subnets	A list of private subnets inside the VPC	string	<list>	no
propagate_private_route_tables_vgw	Should be true if you want route table propagation	string	false	no
propagate_public_route_tables_vgw	Should be true if you want route table propagation	string	false	no
public_route_table_tags	Additional tags for the public route tables	string	<map>	no
public_subnet_tags	Additional tags for the public subnets	string	<map>	no
public_subnets	A list of public subnets inside the VPC	string	<list>	no
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
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
vpn_gateway_id	ID of VPN Gateway to attach to the VPC	string	``	no

Outputs

Name	Description
database_subnet_group	ID of database subnet group
database_subnets	List of IDs of database subnets
database_subnets_cidr_blocks	List of cidr_blocks of database subnets
default_network_acl_id	The ID of the default network ACL
default_route_table_id	The ID of the default route table
default_security_group_id	The ID of the security group created by default on VPC creation
default_vpc_cidr_block	The CIDR block of the VPC
default_vpc_default_network_acl_id	The ID of the default network ACL
default_vpc_default_route_table_id	The ID of the default route table
default_vpc_default_security_group_id	The ID of the security group created by default on VPC creation
default_vpc_enable_dns_hostnames	Whether or not the VPC has DNS hostname support
default_vpc_enable_dns_support	Whether or not the VPC has DNS support
default_vpc_id	Default VPC
default_vpc_instance_tenancy	Tenancy of instances spin up within VPC
default_vpc_main_route_table_id	The ID of the main route table associated with this VPC
elasticache_subnet_group	ID of elasticache subnet group
elasticache_subnet_group_name	Name of elasticache subnet group
elasticache_subnets	List of IDs of elasticache subnets
elasticache_subnets_cidr_blocks	List of cidr_blocks of elasticache subnets
igw_id	Internet Gateway
intra_subnets	List of IDs of intra subnets
intra_subnets_cidr_blocks	List of cidr_blocks of intra subnets
nat_ids	List of allocation ID of Elastic IPs created for AWS NAT Gateway
nat_public_ips	List of public Elastic IPs created for AWS NAT Gateway
natgw_ids	List of NAT Gateway IDs
private_route_table_ids	List of IDs of private route tables
private_subnets	Subnets
private_subnets_cidr_blocks	List of cidr_blocks of private subnets
public_route_table_ids	Route tables
public_subnets	List of IDs of public subnets
public_subnets_cidr_blocks	List of cidr_blocks of public subnets
redshift_subnet_group	ID of redshift subnet group
redshift_subnets	List of IDs of redshift subnets
redshift_subnets_cidr_blocks	List of cidr_blocks of redshift subnets
vgw_id	VPN Gateway
vpc_cidr_block	The CIDR block of the VPC
vpc_enable_dns_hostnames	Whether or not the VPC has DNS hostname support
vpc_enable_dns_support	Whether or not the VPC has DNS support
vpc_endpoint_dynamodb_id	The ID of VPC endpoint for DynamoDB
vpc_endpoint_dynamodb_pl_id	The prefix list for the DynamoDB VPC endpoint.
vpc_endpoint_s3_id	VPC Endpoints
vpc_endpoint_s3_pl_id	The prefix list for the S3 VPC endpoint.
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

Tests

This module has been packaged with awspec tests through test kitchen. To run them:

1. Install rvm and the ruby version specified in the Gemfile.
2. Install bundler and the gems from our Gemfile:

gem install bundler; bundle install

3. Test using bundle exec kitchen test from the root of the repo.

Authors

Module is maintained by Anton Babenko with help from these awesome contributors.

License

Apache 2 Licensed. See LICENSE for full details.