Variable Definitions

9min

Overview
The variable argument block is the main construct for defining variables, their values, and their relationships in a Terraform blueprint configuration. The argument configurations allow for a very wide range of expressive possibility through their various combinations.
The variable argument block supports nine arguments:
Argument
Description
Required
name
The name of the variable, must match the variable defintion in a Terraform module to override it's configuration.
Yes
display_name
A readable display name to show to the consumer, defaults to name.
No
helper_text
Descriptive text shown to the consumer in the collection form giving context and requirements for the values to be provided.
No
type
The type of the variable, must be shortText, radio, checkbox, or map.
No
value
A static value or reference value assigned to the variable.
No
options
An options block defining the options for a radio or checkbox
No
validation_rule
A validation_rule block defining validation rules for the variable.
No
required_values
A list of string values that are required for a list element.
No
conditional
A conditional block defining behavior based on the value of other variables.
No
These arguments are detailed in the sections below.
Example variable definition requesting a string input for the variable application:
Terraform
variable {
  name         = "application"
  display_name = "Application Name"
  helper_text  = "The name of the application this asset is associated with"
}
variable {
  name         = "application"
  display_name = "Application Name"
  helper_text  = "The name of the application this asset is associated with"
}
﻿
Example variable definition defining a static value namespace set to autocloud:
Terraform
variable {
  name         = "namespace"
  display_name = "Asset Namespace"
  helper_text  = "The top level namespace/brand/cost center this asset is associated with"
  value        = "autocloud"
}
variable {
  name         = "namespace"
  display_name = "Asset Namespace"
  helper_text  = "The top level namespace/brand/cost center this asset is associated with"
  value        = "autocloud"
}
﻿
Form Display
The form display arguments name, display_name and helper_text determine how the variable will be displayed to the consumer. For example, imagine this variable is defined in a module:
Terraform
variable "namespace" {
  type        = string
  default     = null
  description = "Namespace, which could be your organization name or abbreviation, e.g. 'eg' or 'cp'"
}
variable "namespace" {
  type        = string
  default     = null
  description = "Namespace, which could be your organization name or abbreviation, e.g. 'eg' or 'cp'"
}
﻿
and a blueprint configuration with this variable block:
Terraform
variable {
  name         = "namespace"
  display_name = "Namespace"
  helper_text  = "The organization namespace the assets will be deployed in"
  value        = "unstyl"
}
variable {
  name         = "namespace"
  display_name = "Namespace"
  helper_text  = "The organization namespace the assets will be deployed in"
  value        = "unstyl"
}
﻿
The consumer form will display this form element:
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Options
Some display elements such as radio buttons require multiple options for the user to choose from. To support this, the options argument block is used. The options block takes one or more option child block to define the choices available to the user. The option block supports the following arguments:
Argument
Description
Required
label
Display text for the option. If no label is provided, the value will be used.
No
value
The value of the option.
Yes
checked
A boolean indicating whether or not the option is checked by default. Only one option may have this argument set to true. Defaults to false, not checked.
No
Example radio:
Terraform
variable {
  name         = "multi_region"
  display_name = "Multi Region Key"
  helper_text  = "Whether or not the KMS key will be deployed as a multi region key"
  type         = "radio"
  options {
    option {
      label   = "Single region key"
      value   = "true"
      checked = false
    }
    option {
      label   = "Multi region key"
      value   = "false"
      checked = true
    }
  }
}
variable {
  name         = "multi_region"
  display_name = "Multi Region Key"
  helper_text  = "Whether or not the KMS key will be deployed as a multi region key"
  type         = "radio"
  options {
    option {
      label   = "Single region key"
      value   = "true"
      checked = false
    }
    option {
      label   = "Multi region key"
      value   = "false"
      checked = true
    }
  }
}
﻿
Validation Rules
Variables may have validation rules applied to them. The validation_rule argument block implements these rules. Currently, only a single rule type is supported. The argument block supports two arguments:
Argument
Description
Required
rule
Name of rule to apply. Currently, only isRequired is supported.
Yes
error_message
An error message shown to the user in the event of validation failure.
Yes
isRequired
The isRequired rule checks to ensure that a value is given for the variable. If not value is provided, validation is failed, and the message provided in the error_message argument is shown to the consumer.
Example:
Terraform
variable {
  name         = "name"
  display_name = "Name"
  helper_text  = "The name of the static site"

  type = "shortText"

  validation_rule {
    rule          = "isRequired"
    error_message = "You must provide a name for this static site."
  }
}
variable {
  name         = "name"
  display_name = "Name"
  helper_text  = "The name of the static site"

  type = "shortText"

  validation_rule {
    rule          = "isRequired"
    error_message = "You must provide a name for this static site."
  }
}
﻿
Conditionals
In many circumstances it is necessary to have the value of an input variable depend on the value of another. For example, the value of a DNS record may depend on the environment that the application is deployed in. To support these use cases, the conditional argument block is used. The block supports the following arguments:
Argument
Description
Required
source
A module variable reference on whose value the conditional will change.
Yes
condition
The value of the source variable for which the content applies.
Yes
content
The content of the variable block when the condition is met. Follows the same syntax as the normal variable block.
Yes
Example:
Terraform
variable {
  name = "cloudfront.ssl_certificate_arn"

  conditional {
    source    = "cloudfront.environment"
    condition = "nonprod"
    content {
      value = "arn:aws:acm:us-east-1:135791113151:certificate/99075784-bddb-11ed-afa1-0242ac120002"                                                               
    }
  }

  conditional {
    source    = "cloudfront.environment"
    condition = "production"
    content {
      value = "arn:aws:acm:us-east-1:246810121416:certificate/a700c172-bddb-11ed-afa1-0242ac120002"
    }
  }
}
variable {
  name = "cloudfront.ssl_certificate_arn"

  conditional {
    source    = "cloudfront.environment"
    condition = "nonprod"
    content {
      value = "arn:aws:acm:us-east-1:135791113151:certificate/99075784-bddb-11ed-afa1-0242ac120002"                                                               
    }
  }

  conditional {
    source    = "cloudfront.environment"
    condition = "production"
    content {
      value = "arn:aws:acm:us-east-1:246810121416:certificate/a700c172-bddb-11ed-afa1-0242ac120002"
    }
  }
}
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Updated 08 Mar 2023

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TABLE OF CONTENTS

Argument	Description	Required
name	The name of the variable, must match the variable defintion in a Terraform module to override it's configuration.	Yes
display_name	A readable display name to show to the consumer, defaults to name.	No
helper_text	Descriptive text shown to the consumer in the collection form giving context and requirements for the values to be provided.	No
type	The type of the variable, must be shortText, radio, checkbox, or map.	No
value	A static value or reference value assigned to the variable.	No
options	An options block defining the options for a radio or checkbox	No
validation_rule	A validation_rule block defining validation rules for the variable.	No
required_values	A list of string values that are required for a list element.	No
conditional	A conditional block defining behavior based on the value of other variables.	No