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Module: 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.

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.

Click to show
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:

Click to show
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"
}
]

Autoscaling group using propagating tagging below (full example: autoscalinggroup)

################################
# 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.

Click to show
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
}

This creates label outputs like this:

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"
})

Variables

Required Variables

Optional Variables

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

additional_tag_map

The merged additional_tag_map

attributes

List of attributes

context

Merged but otherwise unmodified input to this module, to be used as context input to other modules.
Note: this version will have null values as defaults, not the values actually used as defaults.


delimiter

Delimiter between namespace, tenant, environment, stage, name and attributes

descriptors

Map of descriptors as configured by descriptor_formats

enabled

True if module is enabled, false otherwise

environment

Normalized environment

id

Disambiguated ID string restricted to id_length_limit characters in total

id_full

ID string not restricted in length

id_length_limit

The id_length_limit actually used to create the ID, with 0 meaning unlimited

label_order

The naming order actually used to create the ID

name

Normalized name

namespace

Normalized namespace

normalized_context

Normalized context of this module

regex_replace_chars

The regex_replace_chars actually used to create the ID

stage

Normalized stage

tags

Normalized Tag map

tags_as_list_of_maps

This is a list with one map for each tag. Each map contains the tag key,
value, and contents of var.additional_tag_map. Used in the rare cases
where resources need additional configuration information for each tag.


tenant

Normalized tenant

Dependencies

Requirements

  • terraform, version: >= 0.13.0