An Introduction to Terraform Variables: Simplify Your Infrastructure Management

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terraform variables

Are you tired of constantly modifying your Terraform code whenever you need to change a value?

A well-liked tool for organizing infrastructure as code is Terraform. In particular, Terraform variables provide a way to add parameters to your code, making it easier to manage and reuse arguments. However, managing variables can become challenging as your infrastructure grows more complex.

This article will introduce you to Terraform variables, why you should use them, and how they can help you manage your infrastructure more efficiently.

We will cover the basics of variables, how to define and use them, and best practices for working with them. You will have a firm knowledge of Terraform variables and how to apply them to your projects by the time you finish reading this article.

Table Of Content

  1. Introduction
  2. How To Declare TerraForm Variables?
  3. Set Environment Variables
  4. How to Use Terraform Variables
  5. Conclusion
  6. FAQs

What are Terraform Variables, and Why Should You Use Them

When writing Terraform code, you can directly mention literal values (such as server names) as “hardwired” strings as parameters. This greatly simplifies writing Terraform code and gets things done faster.

This approach works as long as the codebase and infrastructure remain small.

However, as the infrastructure grows and the codebase increases in complexity, we need a way to reference values in several places in the code. That’s where Terraform variables come in.

Terraform variables allow us to define a parameter once and then reference it anywhere in the code. As a result, the code is more modular and useful.

Variables in Terraform are an excellent approach to constructing centralized reusable references that are easy to read and bring write-once-use-anywhere capabilities to your Terraform code.

How To Declare TerraForm Variables

In Terraform, variables are declared inside a “variable” named block, with the following basic structure:


Note that the block starts with the keyword “variable”, followed by the variable’s name. In the code, the variable is referred to by this name. This name is used in the code to refer to the variable. Since these names are already reserved for meta arguments, a variable cannot contain the names source, version, providers, count for each lifecycle, depending on, or locals.

Syntax For Defining A Variable Block In Terraform

In practical terms, a Terraform variable block has the following structure:

variable "variable_name" {

type = data_type

default = default_value

description = "description of the variable"


Here, variable_name is the variable’s name, data_type is the variable’s data type (such as string, number, bool, list, map, or object), description is an optional variable description, and the default is the variable’s (if any) default value.

Here’s an example of Terraform variable:

variable "RS" {

description = "System environment name"

type = string

default = "support"


Let’s discuss these arguments in detail.

Default: This option gives the variable a default value. When invoking a module, this value is applied if no other value is assigned to the variable. It should be highlighted that the variable is no longer mandatory if a default value is given.

Description: This argument contains brief information about the variable.

Validation: Block of checks/conditions that is used for validation of conditions.

Sensitive: It hides confidential information the variable contains in the output.

Nullable: It determines if the variable can have a null value inside the module.

Type: The type of values that the variable can accept. A Terraform variable can have several types, including:

  • User-defined types: for instance, an object.
  • Primitive Types: Primitive Types include things like boolean, integer, and string.
  • Complex Types: such as list or map.

Let’s discuss some interesting types you can assign to Terraform variables.


Strings are frequently used to simplify and make complex values more approachable. They identify a single value for each structure.

variable “serial” {

type = string

default = "4000-3000-030070200"


String variables are simple substitutions such as the example given below :


Lists and Maps

A list is a numbered catalog of values, and a map is a collection of keys and values (in the form of strings). Each value in the list and maps may be accessed by the associated index number.

variable “company” {

type = list

default = [“manager”, “emp1", “emp2"]


The associated index number may access each value in the list and maps, as you can in the following example:



Boolean types allow you to use true or false values. For instance, you might want a variable that determines whether to retain the case. The Boolean type in this situation can handle either true or false.

variable “mytest” {

default = true


Set Environment Variables

You can use the variables to set the Terraform environment variables. For this, the environment variables are set in the TF VAR_<variable name> format.

For instance, the value of a Terraform variable called “instance” will be referred to as “TF_VAR_instance“.


How to Use Terraform Variables

Using variables in Terraform code is simple. You just use the name of the variable with the var prefix.


It is important to note that only expressions inside the module where the variable was defined can access this assigned variable value. This is known as the scope of the variable.

What are Variable Definitions Files

There are several ways to assign values to root module variables, like

  • Using the -var option in a command line to specify individual variables using terraform plan and terraform apply commands.
  • As an environment variable
  • In a variable definition file (.tfvars) in a command line when there are several variables declared.

It is a good idea to keep all of your variables in a variable definition file if you have many. This is usually a .tfvars file or a .tfvars.json file. This file is parsed automatically if named ‘terraform.tfvars’.

You can pass this file as a command line argument:

#terraform apply -var-file="redswitches.tfvars"

Additionally, if the file name contains “.auto” before “.tfvars,” as in “testfile.auto.tfvars,” the file will be imported without the need to specify the “var-file” parameter. This is the same as the file titled “terraform.tfvars.”

To prevent the exposure of any sensitive material, please note that we do not place this file in any source control system.

Also Read: Unraveling the Dynamics of Terraform vs Kubernetes


Terraform variables are a great way of simplifying the codebase and reusing values without hardcoding literal strings whenever you need to reference anything. This article covers the essential details of Terraform input variables and how you can use them to define Terraform environment variables.

Let us know how you define and use Terraform variables in your workflows.


Q-1) Is Terraform a proprietary tool?

Terraform is a free and open-source infrastructure as a service (IaaS) software platform that offers a standardized command line interface (CLI) workflow for managing hundreds of cloud services.

Q-2) What is Terraform for DevOps?

Terraform is a tool for securely and efficiently developing, modifying, and versioning infrastructure. Terraform can manage current and popular cloud service providers and unique in-house solutions.

Q-3) Is Terraform a tool or language?

DevOps developers may provide the physical resources an application needs to function dynamically using the open-source infrastructure as code (IaC) software solution Terraform.

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