terraform-null-label

Terraform module designed to generate consistent names and tags for resources. Use terraform-null-label to implement a strict naming convention.

There are 6 inputs considered "labels" or "ID elements" (because the labels are used to construct the ID):

1. namespace
2. tenant
3. environment
4. stage
5. name
6. attributes

This module generates IDs using the following convention by default: {namespace}-{environment}-{stage}-{name}-{attributes}. However, it is highly configurable. The delimiter (e.g. -) is configurable. Each label item is optional (although you must provide at least one). So if you prefer the term stage to environment and do not need tenant, you can exclude them and the label id will look like {namespace}-{stage}-{name}-{attributes}.

• The tenant label was introduced in v0.25.0. To preserve backward compatibility, it is not included by default.
• The attributes input is actually a list of strings and {attributes} expands to the list elements joined by the delimiter.
• If attributes is excluded but namespace, stage, and environment are included, id will look like {namespace}-{environment}-{stage}-{name}. Excluding attributes is discouraged, though, because attributes are the main way modules modify the ID to ensure uniqueness when provisioning the same resource types.
• If you want the label items in a different order, you can specify that, too, with the label_order list.
• You can set a maximum length for the id, and the module will create a (probably) unique name that fits within that length. (The module uses a portion of the MD5 hash of the full id to represent the missing part, so there remains a slight chance of name collision.)
• You can control the letter case of the generated labels which make up the id using var.label_value_case.
• By default, all of the non-empty labels are also exported as tags, whether they appear in the id or not. You can control which labels are exported as tags by setting labels_as_tags to the list of labels you want exported, or the empty list [] if you want no labels exported as tags at all. Tags passed in via the tags variable are always exported, and regardless of settings, empty labels are never exported as tags. You can control the case of the tag names (keys) for the labels using var.label_key_case. Unlike the tags generated from the label inputs, tags passed in via the tags input are not modified.

There is an unfortunate collision over the use of the key name. Cloud Posse uses name in this module to represent the component, such as eks or rds. AWS uses a tag with the key Name to store the full human-friendly identifier of the thing tagged, which this module outputs as id, not name. So when converting input labels to tags, the value of the Name key is set to the module id output, and there is no tag corresponding to the module name output. An empty name label will not prevent the Name tag from being exported.

It's recommended to use one terraform-null-label module for every unique resource of a given resource type. For example, if you have 10 instances, there should be 10 different labels. However, if you have multiple different kinds of resources (e.g. instances, security groups, file systems, and elastic ips), then they can all share the same label assuming they are logically related.

For most purposes, the id output is sufficient to create an ID or label for a resource, and if you want a different ID or a different format, you would instantiate another instance of null-label and configure it accordingly. However, to accomodate situations where you want all the same inputs to generate multiple descriptors, this module provides the descriptors output, which is a map of strings generated according to the format specified by the descriptor_formats input. This feature is intentionally simple and minimally configurable and will not be enhanced to add more features that are already in null-label. See examples/complete/descriptors.tf for examples.

All Cloud Posse Terraform modules use this module to ensure resources can be instantiated multiple times within an account and without conflict.

The Cloud Posse convention is to use labels as follows:

• namespace: A short (3-4 letters) abbreviation of the company name, to ensure globally unique IDs for things like S3 buckets
• tenant: (Rarely needed) When a company creates a dedicated resource per customer, tenant can be used to identify the customer the resource is dedicated to
• environment: A short abbreviation for the AWS region hosting the resource, or gbl for resources like IAM roles that have no region
• stage: The name or role of the account the resource is for, such as prod or dev
• name: The name of the component that owns the resources, such as eks or rds

NOTE: The null originally referred to the primary Terraform provider used in this module. With Terraform 0.12, this module no longer needs any provider, but the name was kept for continuity.

• Releases of this module from 0.23.0 onward only work with Terraform 0.13 or newer.
• Releases of this module from 0.12.0 through 0.22.1 support HCL2 and are compatible with Terraform 0.12 or newer.
• Releases of this module prior to 0.12.0 are compatible with earlier versions of terraform like Terraform 0.11.

[!TIP]

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Usage

Defaults

Cloud Posse Terraform modules share a common context object that is meant to be passed from module to module. The context object is a single object that contains all the input values for terraform-null-label. However, each input value can also be specified individually by name as a standard Terraform variable, and the value of those variables, when set to something other than null, will override the value in the context object. In order to allow chaining of these objects, where the context object input to one module is transformed and passed on to the next module, all the variables default to null or empty collections. The actual default values used when nothing is explicitly set are described in the documentation below.

For example, the default value of delimiter is shown as null, but if you leave it set to null, terraform-null-label will actually use the default delimiter - (hyphen).

A non-obvious but intentional consequence of this design is that once a module sets a non-default value, future modules in the chain cannot reset the value back to the original default. Instead, the new setting becomes the new default for downstream modules. Also, collections are not overwritten, they are merged, so once a tag is added, it will remain in the tag set and cannot be removed, although its value can be overwritten.

Because the purpose of labels_as_tags is primarily to prevent tags from being generated that would conflict with the AWS provider's default_tags, it is an exception to the rule that variables override the setting in the context object. The value in the context object cannot be changed, so that later modules cannot re-enable a problematic tag.

Simple Example

module "eg_prod_bastion_label" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  namespace  = "eg"
  stage      = "prod"
  name       = "bastion"
  attributes = ["public"]
  delimiter  = "-"

  tags = {
    "BusinessUnit" = "XYZ",
    "Snapshot"     = "true"
  }
}

This will create an id with the value of eg-prod-bastion-public because when generating id, the default order is namespace, environment, stage, name, attributes (you can override it by using the label_order variable, see Advanced Example 3).

Now reference the label when creating an instance:

resource "aws_instance" "eg_prod_bastion_public" {
  instance_type = "t1.micro"
  tags          = module.eg_prod_bastion_label.tags
}

Or define a security group:

resource "aws_security_group" "eg_prod_bastion_public" {
  vpc_id = var.vpc_id
  name   = module.eg_prod_bastion_label.id
  tags   = module.eg_prod_bastion_label.tags
  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

Advanced Example

Here is a more complex example with two instances using two different labels. Note how efficiently the tags are defined for both the instance and the security group.

module "eg_prod_bastion_label" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  namespace  = "eg"
  stage      = "prod"
  name       = "bastion"
  delimiter  = "-"

  tags = {
    "BusinessUnit" = "XYZ",
    "Snapshot"     = "true"
  }
}

module "eg_prod_bastion_abc_label" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  attributes = ["abc"]

  tags = {
    "BusinessUnit" = "ABC" # Override the Business Unit tag set in the base label
  }

  # Copy all other fields from the base label
  context = module.eg_prod_bastion_label.context
}

resource "aws_security_group" "eg_prod_bastion_abc" {
  name = module.eg_prod_bastion_abc_label.id
  tags = module.eg_prod_bastion_abc_label.tags
  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_instance" "eg_prod_bastion_abc" {
   instance_type          = "t1.micro"
   tags                   = module.eg_prod_bastion_abc_label.tags
   vpc_security_group_ids = [aws_security_group.eg_prod_bastion_abc.id]
}

module "eg_prod_bastion_xyz_label" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version = "x.x.x"

  attributes = ["xyz"]

  context = module.eg_prod_bastion_label.context
}

resource "aws_security_group" "eg_prod_bastion_xyz" {
  name = module.eg_prod_bastion_xyz_label.id
  tags = module.eg_prod_bastion_xyz_label.tags
  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_instance" "eg_prod_bastion_xyz" {
   instance_type          = "t1.micro"
   tags                   = module.eg_prod_bastion_xyz_label.tags
   vpc_security_group_ids = [aws_security_group.eg_prod_bastion_xyz.id]
}

Advanced Example 2

Here is a more complex example with an autoscaling group that has a different tagging schema than other resources and requires its tags to be in this format, which this module can generate via additional_tag_map and tags_as_list_of_maps:

tags = [
    {
        key = "Name",
        propagate_at_launch = true,
        value = "namespace-stage-name"
    },
    {
        key = "Namespace",
        propagate_at_launch = true,
        value = "namespace"
    },
    {
        key = "Stage",
        propagate_at_launch = true,
        value = "stage"
    }
]

################################
# terraform-null-label example #
################################
module "label" {
  source    = "../../"
  namespace = "cp"
  stage     = "prod"
  name      = "app"

  tags = {
    BusinessUnit = "Finance"
    ManagedBy    = "Terraform"
  }

  additional_tag_map = {
    propagate_at_launch = true
  }
}

#######################
# Launch template     #
#######################
resource "aws_launch_template" "default" {
  # terraform-null-label example used here: Set template name prefix
  name_prefix                           = "${module.label.id}-"
  image_id                              = data.aws_ami.amazon_linux.id
  instance_type                         = "t2.micro"
  instance_initiated_shutdown_behavior  = "terminate"

  vpc_security_group_ids                = [data.aws_security_group.default.id]

  monitoring {
    enabled                             = false
  }
  # terraform-null-label example used here: Set tags on volumes
  tag_specifications {
    resource_type                       = "volume"
    tags                                = module.label.tags
  }
}

######################
# Autoscaling group  #
######################
resource "aws_autoscaling_group" "default" {
  # terraform-null-label example used here: Set ASG name prefix
  name_prefix                           = "${module.label.id}-"
  vpc_zone_identifier                   = data.aws_subnet_ids.all.ids
  max_size                              = 1
  min_size                              = 1
  desired_capacity                      = 1

  launch_template = {
    id                                  = aws_launch_template.default.id
    version                             = "$$Latest"
  }

  # terraform-null-label example used here: Set tags on ASG and EC2 Servers
  tags                                  = module.label.tags_as_list_of_maps
}

Advanced Example 3

See complete example for even more examples.

This example shows how you can pass the context output of one label module to the next label_module, allowing you to create one label that has the base set of values, and then creating every extra label as a derivative of that.

module "label1" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"

  namespace   = "CloudPosse"
  tenant      = "H.R.H"
  environment = "UAT"
  stage       = "build"
  name        = "Winston Churchroom"
  attributes  = ["fire", "water", "earth", "air"]

  label_order = ["name", "tenant", "environment", "stage", "attributes"]

  tags = {
    "City"        = "Dublin"
    "Environment" = "Private"
  }
}

module "label2" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"

  name      = "Charlie"
  tenant    = "" # setting to `null` would have no effect
  stage     = "test"
  delimiter = "+"
  regex_replace_chars = "/[^a-zA-Z0-9-+]/"

  additional_tag_map = {
    propagate_at_launch = true
    additional_tag      = "yes"
  }

  tags = {
    "City"        = "London"
    "Environment" = "Public"
  }

  context   = module.label1.context
}

module "label3" {
  source   = "cloudposse/label/null"
  # Cloud Posse recommends pinning every module to a specific version
  # version     = "x.x.x"

  name      = "Starfish"
  stage     = "release"
  delimiter = "."
  regex_replace_chars = "/[^-a-zA-Z0-9.]/"

  tags = {
    "Eat"    = "Carrot"
    "Animal" = "Rabbit"
  }

  context   = module.label1.context
}

label1 = {
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "-"
  "id" = "winstonchurchroom-hrh-uat-build-fire-water-earth-air"
  "name" = "winstonchurchroom"
  "namespace" = "cloudposse"
  "stage" = "build"
  "tenant" = "hrh"
}
label1_context = {
  "additional_tag_map" = {}
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = tostring(null)
  "enabled" = true
  "environment" = "UAT"
  "id_length_limit" = tonumber(null)
  "label_key_case" = tostring(null)
  "label_order" = tolist([
    "name",
    "tenant",
    "environment",
    "stage",
    "attributes",
  ])
  "label_value_case" = tostring(null)
  "name" = "Winston Churchroom"
  "namespace" = "CloudPosse"
  "regex_replace_chars" = tostring(null)
  "stage" = "build"
  "tags" = {
    "City" = "Dublin"
    "Environment" = "Private"
  }
  "tenant" = "H.R.H"
}
label1_normalized_context = {
  "additional_tag_map" = {}
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "-"
  "enabled" = true
  "environment" = "uat"
  "id_length_limit" = 0
  "label_key_case" = "title"
  "label_order" = tolist([
    "name",
    "tenant",
    "environment",
    "stage",
    "attributes",
  ])
  "label_value_case" = "lower"
  "name" = "winstonchurchroom"
  "namespace" = "cloudposse"
  "regex_replace_chars" = "/[^-a-zA-Z0-9]/"
  "stage" = "build"
  "tags" = {
    "Attributes" = "fire-water-earth-air"
    "City" = "Dublin"
    "Environment" = "Private"
    "Name" = "winstonchurchroom-hrh-uat-build-fire-water-earth-air"
    "Namespace" = "cloudposse"
    "Stage" = "build"
    "Tenant" = "hrh"
  }
  "tenant" = "hrh"
}
label1_tags = tomap({
  "Attributes" = "fire-water-earth-air"
  "City" = "Dublin"
  "Environment" = "Private"
  "Name" = "winstonchurchroom-hrh-uat-build-fire-water-earth-air"
  "Namespace" = "cloudposse"
  "Stage" = "build"
  "Tenant" = "hrh"
})
label2 = {
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "+"
  "id" = "charlie+uat+test+fire+water+earth+air"
  "name" = "charlie"
  "namespace" = "cloudposse"
  "stage" = "test"
  "tenant" = ""
}
label2_context = {
  "additional_tag_map" = {
    "additional_tag" = "yes"
    "propagate_at_launch" = "true"
  }
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "+"
  "enabled" = true
  "environment" = "UAT"
  "id_length_limit" = tonumber(null)
  "label_key_case" = tostring(null)
  "label_order" = tolist([
    "name",
    "tenant",
    "environment",
    "stage",
    "attributes",
  ])
  "label_value_case" = tostring(null)
  "name" = "Charlie"
  "namespace" = "CloudPosse"
  "regex_replace_chars" = "/[^a-zA-Z0-9-+]/"
  "stage" = "test"
  "tags" = {
    "City" = "London"
    "Environment" = "Public"
  }
  "tenant" = ""
}
label2_tags = tomap({
  "Attributes" = "fire+water+earth+air"
  "City" = "London"
  "Environment" = "Public"
  "Name" = "charlie+uat+test+fire+water+earth+air"
  "Namespace" = "cloudposse"
  "Stage" = "test"
})
label2_tags_as_list_of_maps = [
  {
    "additional_tag" = "yes"
    "key" = "Attributes"
    "propagate_at_launch" = "true"
    "value" = "fire+water+earth+air"
  },
  {
    "additional_tag" = "yes"
    "key" = "City"
    "propagate_at_launch" = "true"
    "value" = "London"
  },
  {
    "additional_tag" = "yes"
    "key" = "Environment"
    "propagate_at_launch" = "true"
    "value" = "Public"
  },
  {
    "additional_tag" = "yes"
    "key" = "Name"
    "propagate_at_launch" = "true"
    "value" = "charlie+uat+test+fire+water+earth+air"
  },
  {
    "additional_tag" = "yes"
    "key" = "Namespace"
    "propagate_at_launch" = "true"
    "value" = "cloudposse"
  },
  {
    "additional_tag" = "yes"
    "key" = "Stage"
    "propagate_at_launch" = "true"
    "value" = "test"
  },
]
label3 = {
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "."
  "id" = "starfish.h.r.h.uat.release.fire.water.earth.air"
  "name" = "starfish"
  "namespace" = "cloudposse"
  "stage" = "release"
  "tenant" = "h.r.h"
}
label3_context = {
  "additional_tag_map" = {}
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "."
  "enabled" = true
  "environment" = "UAT"
  "id_length_limit" = tonumber(null)
  "label_key_case" = tostring(null)
  "label_order" = tolist([
    "name",
    "tenant",
    "environment",
    "stage",
    "attributes",
  ])
  "label_value_case" = tostring(null)
  "name" = "Starfish"
  "namespace" = "CloudPosse"
  "regex_replace_chars" = "/[^-a-zA-Z0-9.]/"
  "stage" = "release"
  "tags" = {
    "Animal" = "Rabbit"
    "City" = "Dublin"
    "Eat" = "Carrot"
    "Environment" = "Private"
  }
  "tenant" = "H.R.H"
}
label3_normalized_context = {
  "additional_tag_map" = {}
  "attributes" = tolist([
    "fire",
    "water",
    "earth",
    "air",
  ])
  "delimiter" = "."
  "enabled" = true
  "environment" = "uat"
  "id_length_limit" = 0
  "label_key_case" = "title"
  "label_order" = tolist([
    "name",
    "tenant",
    "environment",
    "stage",
    "attributes",
  ])
  "label_value_case" = "lower"
  "name" = "starfish"
  "namespace" = "cloudposse"
  "regex_replace_chars" = "/[^-a-zA-Z0-9.]/"
  "stage" = "release"
  "tags" = {
    "Animal" = "Rabbit"
    "Attributes" = "fire.water.earth.air"
    "City" = "Dublin"
    "Eat" = "Carrot"
    "Environment" = "Private"
    "Name" = "starfish.h.r.h.uat.release.fire.water.earth.air"
    "Namespace" = "cloudposse"
    "Stage" = "release"
    "Tenant" = "h.r.h"
  }
  "tenant" = "h.r.h"
}
label3_tags = tomap({
  "Animal" = "Rabbit"
  "Attributes" = "fire.water.earth.air"
  "City" = "Dublin"
  "Eat" = "Carrot"
  "Environment" = "Private"
  "Name" = "starfish.h.r.h.uat.release.fire.water.earth.air"
  "Namespace" = "cloudposse"
  "Stage" = "release"
  "Tenant" = "h.r.h"
})

[!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.

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

Providers

No providers.

Modules

No modules.

Resources

No resources.

Inputs

{
  "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
}

[
  "default"
]

Outputs

[!TIP]

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