Awesome

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.

If you are creating subnets inside a VPC, consider using cloudposse/terraform-aws-dynamic-subnets instead.

Screenshots

<img src="images/terraform-aws-multi-az-subnets.png" alt="terraform-aws-multi-az-subnets" />Example of terraform apply outputs

[!TIP]

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Usage

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

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

  namespace  = var.namespace
  stage      = var.stage
  name       = var.name
  cidr_block = var.cidr_block
}

module "public_subnets" {
  source = "cloudposse/multi-az-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  namespace           = var.namespace
  stage               = var.stage
  name                = var.name
  availability_zones  = ["us-east-2a", "us-east-2b", "us-east-2c"]
  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 = "cloudposse/multi-az-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  namespace          = var.namespace
  stage              = var.stage
  name               = var.name
  availability_zones = ["us-east-2a", "us-east-2b", "us-east-2c"]
  vpc_id             = module.vpc.vpc_id
  cidr_block         = local.private_cidr_block
  type               = "private"

  az_ngw_ids = module.public_subnets.az_ngw_ids
}

[!IMPORTANT] In Cloud Posse's examples, we avoid pinning modules to specific versions to prevent discrepancies between the documentation and the latest released versions. However, for your own projects, we strongly advise pinning each module to the exact version you're using. This practice ensures the stability of your infrastructure. Additionally, we recommend implementing a systematic approach for updating versions to avoid unexpected changes.

Examples

Given the following configuration

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

  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 = "cloudposse/multi-az-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  namespace           = var.namespace
  stage               = var.stage
  name                = var.name
  availability_zones  = ["us-east-2a", "us-east-2b", "us-east-2c"]
  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 = "cloudposse/multi-az-subnets/aws"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  namespace           = var.namespace
  stage               = var.stage
  name                = var.name
  availability_zones  = ["us-east-2a", "us-east-2b", "us-east-2c"]
  vpc_id              = module.vpc.vpc_id
  cidr_block          = local.private_cidr_block
  type                = "private"
  az_ngw_ids          = module.public_subnets.az_ngw_ids
}

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-2a = subnet-ea58d78e
  us-east-2b = subnet-556ee131
  us-east-2c = subnet-6f54db0b
}
private_az_subnet_ids = {
  us-east-2a = subnet-376de253
  us-east-2b = subnet-9e53dcfa
  us-east-2c = 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-2a"]

lookup(private_az_subnet_ids, "us-east-2b")

[!TIP]

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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
<a name="requirement_terraform"></a> terraform	>= 0.13.0
<a name="requirement_aws"></a> aws	>= 3.0
<a name="requirement_local"></a> local	>= 1.2
<a name="requirement_null"></a> null	>= 2.0

Providers

Name	Version
<a name="provider_aws"></a> aws	>= 3.0

Modules

Name	Source	Version
<a name="module_private_label"></a> private_label	cloudposse/label/null	0.24.1
<a name="module_public_label"></a> public_label	cloudposse/label/null	0.24.1
<a name="module_this"></a> this	cloudposse/label/null	0.25.0

Resources

Name	Type
aws_eip.public	resource
aws_nat_gateway.public	resource
aws_network_acl.private	resource
aws_network_acl.public	resource
aws_route.default	resource
aws_route.public	resource
aws_route.public_ipv6	resource
aws_route_table.private	resource
aws_route_table.public	resource
aws_route_table_association.private	resource
aws_route_table_association.public	resource
aws_subnet.private	resource
aws_subnet.public	resource

Inputs

Name	Description	Type	Default	Required
<a name="input_additional_tag_map"></a> additional_tag_map	Additional key-value pairs to add to each map in `tags_as_list_of_maps`. Not added to `tags` or `id`.<br/>This is for some rare cases where resources want additional configuration of tags<br/>and therefore take a list of maps with tag key, value, and additional configuration.	`map(string)`	`{}`	no
<a name="input_attributes"></a> attributes	ID element. Additional attributes (e.g. `workers` or `cluster`) to add to `id`,<br/>in the order they appear in the list. New attributes are appended to the<br/>end of the list. The elements of the list are joined by the `delimiter`<br/>and treated as a single ID element.	`list(string)`	`[]`	no
<a name="input_availability_zones"></a> availability_zones	List of Availability Zones (e.g. `['us-east-1a', 'us-east-1b', 'us-east-1c']`)	`list(string)`	n/a	yes
<a name="input_az_ngw_ids"></a> 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.<br/>You should either supply one NAT Gateway ID for each AZ in `var.availability_zones` or leave the map empty.<br/>If empty, no default egress route will be created and you will have to create your own using `aws_route`.	`map(string)`	`{}`	no
<a name="input_cidr_block"></a> cidr_block	Base CIDR block which is divided into subnet CIDR blocks (e.g. `10.0.0.0/16`)	`string`	n/a	yes
<a name="input_context"></a> context	Single object for setting entire context at once.<br/>See description of individual variables for details.<br/>Leave string and numeric variables as `null` to use default value.<br/>Individual variable settings (non-null) override settings in context object,<br/>except for attributes, tags, and additional_tag_map, which are merged.	`any`	<pre>{<br/> "additional_tag_map": {},<br/> "attributes": [],<br/> "delimiter": null,<br/> "descriptor_formats": {},<br/> "enabled": true,<br/> "environment": null,<br/> "id_length_limit": null,<br/> "label_key_case": null,<br/> "label_order": [],<br/> "label_value_case": null,<br/> "labels_as_tags": [<br/> "unset"<br/> ],<br/> "name": null,<br/> "namespace": null,<br/> "regex_replace_chars": null,<br/> "stage": null,<br/> "tags": {},<br/> "tenant": null<br/>}</pre>	no
<a name="input_delimiter"></a> delimiter	Delimiter to be used between ID elements.<br/>Defaults to `-` (hyphen). Set to `""` to use no delimiter at all.	`string`	`null`	no
<a name="input_descriptor_formats"></a> descriptor_formats	Describe additional descriptors to be output in the `descriptors` output map.<br/>Map of maps. Keys are names of descriptors. Values are maps of the form<br/>`{<br/> format = string<br/> labels = list(string)<br/>}`<br/>(Type is `any` so the map values can later be enhanced to provide additional options.)<br/>`format` is a Terraform format string to be passed to the `format()` function.<br/>`labels` is a list of labels, in order, to pass to `format()` function.<br/>Label values will be normalized before being passed to `format()` so they will be<br/>identical to how they appear in `id`.<br/>Default is `{}` (`descriptors` output will be empty).	`any`	`{}`	no
<a name="input_enabled"></a> enabled	Set to false to prevent the module from creating any resources	`bool`	`null`	no
<a name="input_environment"></a> environment	ID element. Usually used for region e.g. 'uw2', 'us-west-2', OR role 'prod', 'staging', 'dev', 'UAT'	`string`	`null`	no
<a name="input_id_length_limit"></a> id_length_limit	Limit `id` to this many characters (minimum 6).<br/>Set to `0` for unlimited length.<br/>Set to `null` for keep the existing setting, which defaults to `0`.<br/>Does not affect `id_full`.	`number`	`null`	no
<a name="input_igw_id"></a> igw_id	Internet Gateway ID that is used as a default route when creating public subnets (e.g. `igw-9c26a123`)	`string`	`""`	no
<a name="input_ipv6_cidr_block"></a> ipv6_cidr_block	Base IPv6 CIDR block which is divided into /64 subnet CIDR blocks	`string`	`null`	no
<a name="input_ipv6_enabled"></a> ipv6_enabled	Flag to enable/disable IPv6 creation in public subnets	`bool`	`false`	no
<a name="input_label_key_case"></a> label_key_case	Controls the letter case of the `tags` keys (label names) for tags generated by this module.<br/>Does not affect keys of tags passed in via the `tags` input.<br/>Possible values: `lower`, `title`, `upper`.<br/>Default value: `title`.	`string`	`null`	no
<a name="input_label_order"></a> label_order	The order in which the labels (ID elements) appear in the `id`.<br/>Defaults to ["namespace", "environment", "stage", "name", "attributes"].<br/>You can omit any of the 6 labels ("tenant" is the 6th), but at least one must be present.	`list(string)`	`null`	no
<a name="input_label_value_case"></a> label_value_case	Controls the letter case of ID elements (labels) as included in `id`,<br/>set as tag values, and output by this module individually.<br/>Does not affect values of tags passed in via the `tags` input.<br/>Possible values: `lower`, `title`, `upper` and `none` (no transformation).<br/>Set this to `title` and set `delimiter` to `""` to yield Pascal Case IDs.<br/>Default value: `lower`.	`string`	`null`	no
<a name="input_labels_as_tags"></a> labels_as_tags	Set of labels (ID elements) to include as tags in the `tags` output.<br/>Default is to include all labels.<br/>Tags with empty values will not be included in the `tags` output.<br/>Set to `[]` to suppress all generated tags.<br/>Notes:<br/> The value of the `name` tag, if included, will be the `id`, not the `name`.<br/> Unlike other `null-label` inputs, the initial setting of `labels_as_tags` cannot be<br/> changed in later chained modules. Attempts to change it will be silently ignored.	`set(string)`	<pre>[<br/> "default"<br/>]</pre>	no
<a name="input_max_subnets"></a> max_subnets	Maximum number of subnets that can be created. The variable is used for CIDR blocks calculation	`string`	`"6"`	no
<a name="input_name"></a> name	ID element. Usually the component or solution name, e.g. 'app' or 'jenkins'.<br/>This is the only ID element not also included as a `tag`.<br/>The "name" tag is set to the full `id` string. There is no tag with the value of the `name` input.	`string`	`null`	no
<a name="input_namespace"></a> namespace	ID element. Usually an abbreviation of your organization name, e.g. 'eg' or 'cp', to help ensure generated IDs are globally unique	`string`	`null`	no
<a name="input_nat_gateway_enabled"></a> nat_gateway_enabled	Flag to enable/disable NAT Gateways creation in public subnets	`string`	`"true"`	no
<a name="input_private_network_acl_egress"></a> private_network_acl_egress	Egress network ACL rules	`list(map(string))`	<pre>[<br/> {<br/> "action": "allow",<br/> "cidr_block": "0.0.0.0/0",<br/> "from_port": 0,<br/> "protocol": "-1",<br/> "rule_no": 100,<br/> "to_port": 0<br/> }<br/>]</pre>	no
<a name="input_private_network_acl_id"></a> private_network_acl_id	Network ACL ID that is added to the private subnets. If empty, a new ACL will be created	`string`	`""`	no
<a name="input_private_network_acl_ingress"></a> private_network_acl_ingress	Egress network ACL rules	`list(map(string))`	<pre>[<br/> {<br/> "action": "allow",<br/> "cidr_block": "0.0.0.0/0",<br/> "from_port": 0,<br/> "protocol": "-1",<br/> "rule_no": 100,<br/> "to_port": 0<br/> }<br/>]</pre>	no
<a name="input_public_network_acl_egress"></a> public_network_acl_egress	Egress network ACL rules	`list(map(string))`	<pre>[<br/> {<br/> "action": "allow",<br/> "cidr_block": "0.0.0.0/0",<br/> "from_port": 0,<br/> "protocol": "-1",<br/> "rule_no": 100,<br/> "to_port": 0<br/> }<br/>]</pre>	no
<a name="input_public_network_acl_id"></a> public_network_acl_id	Network ACL ID that is added to the public subnets. If empty, a new ACL will be created	`string`	`""`	no
<a name="input_public_network_acl_ingress"></a> public_network_acl_ingress	Egress network ACL rules	`list(map(string))`	<pre>[<br/> {<br/> "action": "allow",<br/> "cidr_block": "0.0.0.0/0",<br/> "from_port": 0,<br/> "protocol": "-1",<br/> "rule_no": 100,<br/> "to_port": 0<br/> }<br/>]</pre>	no
<a name="input_regex_replace_chars"></a> regex_replace_chars	Terraform regular expression (regex) string.<br/>Characters matching the regex will be removed from the ID elements.<br/>If not set, `"/[^a-zA-Z0-9-]/"` is used to remove all characters other than hyphens, letters and digits.	`string`	`null`	no
<a name="input_stage"></a> stage	ID element. Usually used to indicate role, e.g. 'prod', 'staging', 'source', 'build', 'test', 'deploy', 'release'	`string`	`null`	no
<a name="input_tags"></a> tags	Additional tags (e.g. `{'BusinessUnit': 'XYZ'}`).<br/>Neither the tag keys nor the tag values will be modified by this module.	`map(string)`	`{}`	no
<a name="input_tenant"></a> tenant	ID element _(Rarely used, not included by default)_. A customer identifier, indicating who this instance of a resource is for	`string`	`null`	no
<a name="input_type"></a> type	Type of subnets to create (`private` or `public`)	`string`	`"private"`	no
<a name="input_vpc_id"></a> vpc_id	VPC ID	`string`	n/a	yes

Outputs

Name	Description
<a name="output_az_ngw_ids"></a> az_ngw_ids	Map of AZ names to NAT Gateway IDs (only for public subnets)
<a name="output_az_route_table_ids"></a> az_route_table_ids	Map of AZ names to Route Table IDs
<a name="output_az_subnet_arns"></a> az_subnet_arns	Map of AZ names to subnet ARNs
<a name="output_az_subnet_cidr_blocks"></a> az_subnet_cidr_blocks	Map of AZ names to subnet CIDR blocks
<a name="output_az_subnet_ids"></a> az_subnet_ids	Map of AZ names to subnet IDs
<a name="output_az_subnet_ipv6_cidr_blocks"></a> az_subnet_ipv6_cidr_blocks	Map of AZ names to subnet IPv6 CIDR blocks
<a name="output_az_subnet_map"></a> az_subnet_map	Map of AZ names to map of information about subnets

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.

✨ Contributing

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Many thanks to our outstanding contributors:

For 🐛 bug reports & feature requests, please use the issue tracker.

In general, PRs are welcome. We follow the typical "fork-and-pull" Git workflow.

Review our Code of Conduct and Contributor Guidelines.
Fork the repo on GitHub
Clone the project to your own machine
Commit changes to your own branch
Push your work back up to your fork
Submit a Pull Request so that we can review your changes

NOTE: Be sure to merge the latest changes from "upstream" before making a pull request!

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Complete license is available in the LICENSE file.

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