Input variable precedence order in Terraform - Mini Project: Build & Apply

Input Variable Precedence Order in Terraform

📖 Scenario: You are setting up a Terraform configuration to deploy a simple cloud resource. You want to understand how Terraform decides which input variable value to use when multiple sources provide values.

🎯 Goal: Build a Terraform configuration that defines an input variable and demonstrates the precedence order of variable values from different sources.

📋 What You'll Learn

Define a Terraform variable with a default value

Override the variable value using a terraform.tfvars file

Override the variable value using an environment variable

Use the variable in a resource or output to confirm the final value

💡 Why This Matters

🌍 Real World

Understanding variable precedence helps avoid configuration errors and unexpected deployments in real cloud infrastructure projects.

💼 Career

Cloud engineers and DevOps professionals frequently manage Terraform variables to customize deployments across environments.

1

Define a Terraform variable with a default value

Create a Terraform variable called region with the default value us-west-1 inside a file named variables.tf.

Terraform

# Define the variable 'region' with default 'us-west-1'
# Your code here

Need a hint?

Use the variable block with default set to "us-west-1".

2

Override the variable value using a terraform.tfvars file

Create a file named terraform.tfvars and set the variable region to us-east-1 inside it.

Terraform

variable "region" {
  type    = string
  default = "us-west-1"
}

# Create terraform.tfvars file with region = "us-east-1"
# Your code here

Need a hint?

In terraform.tfvars, assign region = "us-east-1".

3

Override the variable value using an environment variable

Set the environment variable TF_VAR_region to eu-central-1 to override the variable region value.

Terraform

variable "region" {
  type    = string
  default = "us-west-1"
}

# terraform.tfvars content:
region = "us-east-1"

# Set environment variable TF_VAR_region to "eu-central-1"
# Your code here

Need a hint?

Use your shell to set TF_VAR_region to "eu-central-1" before running Terraform.

4

Use the variable in an output to confirm the final value

Create an output called final_region that outputs the value of the variable region.

Terraform

variable "region" {
  type    = string
  default = "us-west-1"
}

# terraform.tfvars content:
region = "us-east-1"

# Environment variable set outside Terraform:
# export TF_VAR_region="eu-central-1"

output "final_region" {
  # Your code here
}

Need a hint?

Use an output block with value = var.region.