terraform/website/source/docs/configuration/variables.html.md

layout	page_title	sidebar_current	description
docs	Configuring Variables	docs-config-variables	Variables define the parameterization of Terraform configurations. Variables can be overridden via the CLI. Variable usage is covered in more detail in the getting started guide. This page covers configuration syntax for variables.

Variable Configuration

Variables define the parameterization of Terraform configurations. Variables can be overridden via the CLI. Variable usage is covered in more detail in the getting started guide. This page covers configuration syntax for variables.

This page assumes you're familiar with the configuration syntax already.

Example

A variable configuration looks like the following:

variable "key" {
    type = "string"
}

variable "images" {
    type = "map"

	default = {
		us-east-1 = "image-1234"
		us-west-2 = "image-4567"
	}
}

Description

The variable block configures a single input variable for a Terraform configuration. Multiple variables blocks can be used to add multiple variables.

The name given to the variable block is the name used to set the variable via the CLI as well as reference the variable throughout the Terraform configuration.

Within the block (the { }) is configuration for the variable. These are the parameters that can be set:

• type (optional) - If set this defines the type of the variable. Valid values are string and map. In older versions of Terraform this parameter did not exist, and the type was inferred from the default value, defaulting to string if no default was set. If a type is not specified, the previous behavior is maintained. It is recommended to set variable types explicitly in preference to relying on inferrence - this allows variables of type map to be set in the terraform.tfvars file without requiring a default value to be set.

• default (optional) - If set, this sets a default value for the variable. If this isn't set, the variable is required and Terraform will error if not set. The default value can be a string or a mapping. This is covered in more detail below.

• description (optional) - A human-friendly description for the variable. This is primarily for documentation for users using your Terraform configuration. A future version of Terraform will expose these descriptions as part of some Terraform CLI command.

---

Default values can be either strings or maps, and if specified must match the declared type of the variable. If no value is supplied for a variable of type map, the values must be supplied in a terraform.tfvars file - they cannot be input via the console.

String values are simple and represent a basic key to value mapping where the key is the variable name. An example is:

variable "key" {
    type = "string"

	default = "value"
}

A map allows a key to contain a lookup table. This is useful for some values that change depending on some external pivot. A common use case for this is mapping cloud images to regions. An example:

variable "images" {
    type = "map"

	default = {
		us-east-1 = "image-1234"
		us-west-2 = "image-4567"
	}
}

The usage of maps, strings, etc. is documented fully in the interpolation syntax page.

Environment Variables

Environment variables can be used to set the value of a variable. The key of the environment variable must be TF_VAR_name and the value is the value of the variable.

For example, given the configuration below:

variable "image" {}

The variable can be set via an environment variable:

$ TF_VAR_image=foo terraform apply
...

Syntax

The full syntax is:

variable NAME {
	[type = TYPE]
	[default = DEFAULT]
	[description = DESCRIPTION]
}

where DEFAULT is:

VALUE

{
	KEY = VALUE
	...
}