README.yaml

name: terraform-null-label
tags:
  - aws
  - terraform
  - terraform-modules
  - naming-convention
  - name
  - namespace
  - stage
categories:
  - terraform-modules/supported
license: APACHE2
github_repo: cloudposse/terraform-null-label
badges:
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    image: https://slack.cloudposse.com/for-the-badge.svg
    url: https://slack.cloudposse.com
description: |-
  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
  1. tenant
  1. environment
  1. stage
  1. name
  1. 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](examples/complete/descriptors.tf) for examples.

  All [Cloud Posse Terraform modules](https://github.com/cloudposse?utf8=%E2%9C%93&q=terraform-&type=&language=) 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](https://github.com/cloudposse/terraform-aws-utils/#introduction) 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](https://www.terraform.io/docs/providers/null/index.html) 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`](https://github.com/hashicorp/terraform-provider-aws/issues/19204), 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

  ```hcl
  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](#advanced-example-3)).

  Now reference the label when creating an instance:

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

  Or define a security group:

  ```hcl
  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.

  <details><summary>Click to show</summary>

  ```hcl
  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]
  }
  ```

  </details>

  ### 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`:

  <details><summary>Click to show</summary>

  ```hcl
  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](examples/autoscalinggroup/main.tf))

  ```hcl
  ################################
  # 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
  }
  ```

  </details>

  ### Advanced Example 3

  See [complete example](./examples/complete) 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.

  <details><summary>Click to show</summary>

  ```hcl
  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:

  ```hcl
  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"
  })

  ```

  </details>

include:
  - docs/targets.md
  - docs/terraform.md
contributors: []