Gain insights into Infrastructure as Code with Terraform, sharpen your skills, and prepare for the HashiCorp Terraform Associate certification in a cloud-agnostic way.

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This course is designed to help learners obtain the Terraform Associate certification from HashiCorp. 

You’ve likely picked up this course because you dabbled in Terraform as a hobbyist or in a
development environment, and you’re excited about the possibilities of deploying Infrastructure 
as Code (IaC). It will enable you to sharpen your skills and prove your knowledge with a certification from HashiCorp. Terraform is an amazing tool to deploy Infrastructure as Code in a cloud-agnostic way. We’re excited to share our accumulated knowledge with you through this course.

HashiCorp Terraform Certified Associate Preparation Guide

Variables are defined in a Terraform configuration. We can supply values for those variables at runtime or set a default value for the variable to use. Terraform requires that we supply a default value for a variable at runtime if we haven’t already done so.. Failing to supply a value will cause the relevant command to error out.

At its most basic, a variable can be defined with a name label and without any arguments:



![](/api/collection/10370001/6444696643043328/page/6214933869494272/image/5170680164777984?page_type=collection_lesson)

Let's define some more information about our `aws_region`:


variable "aws_region" {
    type        = string
    default     = "us-east-1"
    description = "The AWS region to use for this configuration"
}

We defined what data type to expect (`string`) and what value to default to, and we gave a description for ourselves and others who might use this configuration. Providing a data type for the variable means that Terraform can do some validation to make sure the correct data type is being provided. It’s not full-blown data validation, but it’s better than nothing!

>Note: Terraform 0.13 introduced variable validation as a new feature. When using variable `validation`, we add a validation block to the `variable` block that must evaluate to `true` or `false`. A full explanation of variable validation is beyond the scope of this course, but it’s good to know that the feature exists.

We can also set a variable as `sensitive`, which means that the value stored in the variable isn’t shown in cleartext in logging, terminal output, or plan files. The sensitivity of a value can be altered using the `sensitive` and  `nonsensitive` functions. The sensitivity of a value is respected by functions that operate on the value and by any generated objects that include the value.

# Submit values for variables

Variable values are submitted at runtime through several possible means. Here’s a handy list of our options:

1. We can set environment variables with the prefix `TF_VAR_` followed by the variable name.

2. We can place a `terraform.tfvars` or `terraform.tfvars.json` file in the same directory as the configuration.

3. We can place a file ending with `.auto.tfvars` or `.auto.tfvars.json` in the same directory as the configuration.

4. We can use the `-var-file` flag with the path to a file containing the key/value pairs.

5. We can use the `-var` flag with a key/value pair (`aws_region=us-west-1`).

6. We can type the variable values in when prompted at the command line.


# Order of evaluation

There are many options to choose from, and we can mix and match at will.. Terraform does have an order of precedence for evaluating the submitted values, which corresponds to the reverse order of the list above. The latter options take precedence over earlier options, so if we define a variable value in an environment variable and submit a different value for the same variable using the `-var` flag, the value submitted with the `-var` flag takes precedence. At the command line level, the last value submitted for a value takes precedence.

With values applied to our variables, we can now use those variables by referencing them in the rest of the configuration. We’ll explore that process more when we learn about  [resource addressing](https://www.educative.io/courses/hashicorp-terraform-certified-associate-preparation-guide/resource-addressing-and-resource-parameters-to-connect-resources).


# Key takeaways

Variables are how values are submitted to a Terraform configuration. There are many ways to submit a value, and there’s an order of evaluation, with the last value taking precedence.


Learn how to define and use input variables.

Introduction to the Course

Introduction to Infrastructure as Code

Basics of Terraform

Outside the Workflow: Using the Terraform CLI

Terraform Modules

Navigate Terraform Workflow

Implement and Maintain State

Read, Generate, and Modify Configuration

Understand Terraform Enterprise Capabilities

Conclusion

Use of Input Variables

How to define input variables