Module: 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.

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

Screenshots

Example of terraform apply outputs

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
}

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")

Variables

Required Variables

availability_zones (list(string)) required

List of Availability Zones (e.g. ['us-east-1a', 'us-east-1b', 'us-east-1c'])

cidr_block (string) required

Base CIDR block which is divided into subnet CIDR blocks (e.g. 10.0.0.0/16)

vpc_id (string) required

VPC ID

Optional Variables

az_ngw_ids (map(string)) optional

Only for private subnets. Map of AZ names to NAT Gateway IDs that are used as default routes when creating private subnets.
You should either supply one NAT Gateway ID for each AZ in var.availability_zones or leave the map empty.
If empty, no default egress route will be created and you will have to create your own using aws_route.

Default value: { }

igw_id (string) optional

Internet Gateway ID that is used as a default route when creating public subnets (e.g. igw-9c26a123)

Default value: ""

ipv6_cidr_block (string) optional

Base IPv6 CIDR block which is divided into /64 subnet CIDR blocks

Default value: null

ipv6_enabled (bool) optional

Flag to enable/disable IPv6 creation in public subnets

Default value: false

max_subnets (string) optional

Maximum number of subnets that can be created. The variable is used for CIDR blocks calculation

Default value: "6"

nat_gateway_enabled (string) optional

Flag to enable/disable NAT Gateways creation in public subnets

Default value: "true"

private_network_acl_egress (list(map(string))) optional

Egress network ACL rules

Default value:

[
  {
    "action": "allow",
    "cidr_block": "0.0.0.0/0",
    "from_port": 0,
    "protocol": "-1",
    "rule_no": 100,
    "to_port": 0
  }
]

private_network_acl_id (string) optional

Network ACL ID that is added to the private subnets. If empty, a new ACL will be created

Default value: ""

private_network_acl_ingress (list(map(string))) optional

Egress network ACL rules

Default value:

[
  {
    "action": "allow",
    "cidr_block": "0.0.0.0/0",
    "from_port": 0,
    "protocol": "-1",
    "rule_no": 100,
    "to_port": 0
  }
]

public_network_acl_egress (list(map(string))) optional

Egress network ACL rules

Default value:

[
  {
    "action": "allow",
    "cidr_block": "0.0.0.0/0",
    "from_port": 0,
    "protocol": "-1",
    "rule_no": 100,
    "to_port": 0
  }
]

public_network_acl_id (string) optional

Network ACL ID that is added to the public subnets. If empty, a new ACL will be created

Default value: ""

public_network_acl_ingress (list(map(string))) optional

Egress network ACL rules

Default value:

[
  {
    "action": "allow",
    "cidr_block": "0.0.0.0/0",
    "from_port": 0,
    "protocol": "-1",
    "rule_no": 100,
    "to_port": 0
  }
]

type (string) optional

Type of subnets to create (private or public)

Default value: "private"

Context Variables

The following variables are defined in the context.tf file of this module and part of the terraform-null-label pattern.

additional_tag_map (map(string)) optional

Additional key-value pairs to add to each map in tags_as_list_of_maps. Not added to tags or id.
This is for some rare cases where resources want additional configuration of tags
and therefore take a list of maps with tag key, value, and additional configuration.

Required: No

Default value: { }

attributes (list(string)) optional

ID element. Additional attributes (e.g. workers or cluster) to add to id,
in the order they appear in the list. New attributes are appended to the
end of the list. The elements of the list are joined by the delimiter
and treated as a single ID element.

Required: No

Default value: [ ]

context (any) optional

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.

Required: No

Default value:

{
  "additional_tag_map": {},
  "attributes": [],
  "delimiter": null,
  "descriptor_formats": {},
  "enabled": true,
  "environment": null,
  "id_length_limit": null,
  "label_key_case": null,
  "label_order": [],
  "label_value_case": null,
  "labels_as_tags": [
    "unset"
  ],
  "name": null,
  "namespace": null,
  "regex_replace_chars": null,
  "stage": null,
  "tags": {},
  "tenant": null
}

delimiter (string) optional

Delimiter to be used between ID elements.
Defaults to - (hyphen). Set to "" to use no delimiter at all.

Required: No

Default value: null

descriptor_formats (any) optional

Describe additional descriptors to be output in the descriptors output map.
Map of maps. Keys are names of descriptors. Values are maps of the form
\{<br/> format = string<br/> labels = list(string)<br/> \}
(Type is any so the map values can later be enhanced to provide additional options.)
format is a Terraform format string to be passed to the format() function.
labels is a list of labels, in order, to pass to format() function.
Label values will be normalized before being passed to format() so they will be
identical to how they appear in id.
Default is {} (descriptors output will be empty).

Required: No

Default value: { }

enabled (bool) optional

Set to false to prevent the module from creating any resources
Required: No

Default value: null

environment (string) optional

ID element. Usually used for region e.g. 'uw2', 'us-west-2', OR role 'prod', 'staging', 'dev', 'UAT'
Required: No

Default value: null

id_length_limit (number) optional

Limit id to this many characters (minimum 6).
Set to 0 for unlimited length.
Set to null for keep the existing setting, which defaults to 0.
Does not affect id_full.

Required: No

Default value: null

label_key_case (string) optional

Controls the letter case of the tags keys (label names) for tags generated by this module.
Does not affect keys of tags passed in via the tags input.
Possible values: lower, title, upper.
Default value: title.

Required: No

Default value: null

label_order (list(string)) optional

The order in which the labels (ID elements) appear in the id.
Defaults to ["namespace", "environment", "stage", "name", "attributes"].
You can omit any of the 6 labels ("tenant" is the 6th), but at least one must be present.

Required: No

Default value: null

label_value_case (string) optional

Controls the letter case of ID elements (labels) as included in id,
set as tag values, and output by this module individually.
Does not affect values of tags passed in via the tags input.
Possible values: lower, title, upper and none (no transformation).
Set this to title and set delimiter to "" to yield Pascal Case IDs.
Default value: lower.

Required: No

Default value: null

labels_as_tags (set(string)) optional

Set of labels (ID elements) to include as tags in the tags output.
Default is to include all labels.
Tags with empty values will not be included in the tags output.
Set to [] to suppress all generated tags.
Notes:
The value of the name tag, if included, will be the id, not the name.
Unlike other null-label inputs, the initial setting of labels_as_tags cannot be
changed in later chained modules. Attempts to change it will be silently ignored.

Required: No

Default value:

[
  "default"
]

name (string) optional

ID element. Usually the component or solution name, e.g. 'app' or 'jenkins'.
This is the only ID element not also included as a tag.
The "name" tag is set to the full id string. There is no tag with the value of the name input.

Required: No

Default value: null

namespace (string) optional

ID element. Usually an abbreviation of your organization name, e.g. 'eg' or 'cp', to help ensure generated IDs are globally unique
Required: No

Default value: null

regex_replace_chars (string) optional

Terraform regular expression (regex) string.
Characters matching the regex will be removed from the ID elements.
If not set, "/[^a-zA-Z0-9-]/" is used to remove all characters other than hyphens, letters and digits.

Required: No

Default value: null

stage (string) optional

ID element. Usually used to indicate role, e.g. 'prod', 'staging', 'source', 'build', 'test', 'deploy', 'release'
Required: No

Default value: null

tags (map(string)) optional

Additional tags (e.g. {'BusinessUnit': 'XYZ'}).
Neither the tag keys nor the tag values will be modified by this module.

Required: No

Default value: { }

tenant (string) optional

ID element (Rarely used, not included by default). A customer identifier, indicating who this instance of a resource is for
Required: No

Default value: null

Outputs

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_cidr_blocks

Map of AZ names to subnet CIDR blocks

az_subnet_ids

Map of AZ names to subnet IDs

az_subnet_ipv6_cidr_blocks

Map of AZ names to subnet IPv6 CIDR blocks

az_subnet_map

Map of AZ names to map of information about subnets

Dependencies

Requirements

• terraform, version: >= 0.13.0
• aws, version: >= 3.0
• local, version: >= 1.2
• null, version: >= 2.0

Providers

• aws, version: >= 3.0

Modules

Name	Version	Source	Description
private_label	0.24.1	cloudposse/label/null	n/a
public_label	0.24.1	cloudposse/label/null	n/a
this	0.25.0	cloudposse/label/null	n/a

Resources

The following resources are used by this module:

• 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)

Data Sources

The following data sources are used by this module: