Environment variables (TF_VAR_) in Terraform - Mini Project: Build & Apply

Using Environment Variables (TF_VAR_) in Terraform

📖 Scenario: You are setting up a Terraform configuration to create a cloud resource. To keep your configuration flexible and secure, you want to use environment variables to pass values into Terraform variables.

🎯 Goal: Build a Terraform configuration that uses environment variables prefixed with TF_VAR_ to set variable values without hardcoding them in the configuration files.

📋 What You'll Learn

Create a Terraform variable named region with a default value

Set an environment variable named TF_VAR_region to override the default

Use the region variable in a Terraform resource configuration

Apply the configuration to verify the environment variable is used

💡 Why This Matters

🌍 Real World

Using environment variables to configure Terraform variables allows teams to keep sensitive or environment-specific data out of code files, making deployments safer and more flexible.

💼 Career

Cloud engineers and DevOps professionals often use environment variables to manage infrastructure configurations securely and efficiently across different environments.

1

Define a Terraform variable region

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

Terraform

# Your code here

Hint

This variable block defines a string variable named region with a default value.

2

Set the environment variable TF_VAR_region

Set an environment variable named TF_VAR_region with the value us-east-2 in your shell before running Terraform. Write this exact command for a Unix-like shell:

Terraform

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

# Your code here

Hint

Use export TF_VAR_region="us-east-2" to set the environment variable in bash or similar shells.

3

Use the region variable in a Terraform provider block

In a file called main.tf, write a Terraform provider block for AWS that uses the variable region for its region attribute. Use this exact syntax:

Terraform

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

# Set environment variable in Unix shell
export TF_VAR_region="us-east-2"

# Your code here

Hint

The provider block tells Terraform which AWS region to use, referencing the variable region.

4

Add a simple AWS S3 bucket resource using the region variable

In main.tf, add a resource block to create an AWS S3 bucket named my-tf-bucket with the bucket name my-tf-bucket-12345. Use the region variable indirectly by relying on the provider configuration. Write exactly this resource block:

Terraform

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

# Set environment variable in Unix shell
export TF_VAR_region="us-east-2"

provider "aws" {
  region = var.region
}

# Your code here

Hint

This resource creates a private S3 bucket. The region is set by the provider using the variable.

Practice

1. What is the purpose of using environment variables with the TF_VAR_ prefix in Terraform?

easy

A. To set Terraform input variables without hardcoding them in configuration files

B. To define backend storage for Terraform state files

C. To specify the Terraform provider version

D. To enable debugging output during Terraform runs

Solution

1. Step 1: Understand Terraform variable usage

   Terraform variables allow customization of configurations without changing code files.

2. Step 2: Role of TF_VAR_ prefix

   Environment variables prefixed with TF_VAR_ automatically set Terraform input variables, keeping code clean and secure.

3. Final Answer:

   To set Terraform input variables without hardcoding them in configuration files -> Option A

4. Quick Check:

   Environment variables with TF_VAR_ prefix set variables [OK]

Hint: TF_VAR_ prefix sets Terraform variables via environment [OK]

Common Mistakes:

• Confusing TF_VAR_ with backend configuration
• Using TF_VAR_ to set provider versions
• Expecting TF_VAR_ to enable debug logs

2. Which of the following is the correct way to set a Terraform variable named region using an environment variable?

easy

A. TF_VARregion=us-west-2

B. set TF_VAR-region=us-west-2

C. export TF_VAR_region=us-west-2

D. terraform var region=us-west-2

Solution

1. Step 1: Identify correct environment variable syntax

   Terraform expects environment variables for variables to be prefixed with TF_VAR_ followed by the variable name.

2. Step 2: Correct shell export command

   In Unix-like shells, export TF_VAR_region=us-west-2 correctly sets the variable.

3. Final Answer:

   export TF_VAR_region=us-west-2 -> Option C

4. Quick Check:

   Use export TF_VAR_variable=value [OK]

Hint: Use export TF_VAR_variable=value to set variables [OK]

Common Mistakes:

• Using dash instead of underscore in TF_VAR_ prefix
• Missing export keyword in Unix shell
• Trying to set variables with terraform command directly

3. Given the Terraform variable declaration:

variable "instance_type" { default = "t2.micro" }

and the environment variable set as export TF_VAR_instance_type=t3.medium, what will be the value of var.instance_type during Terraform apply?

medium

A. "t2.micro" (default value)

B. "t3.medium" (from environment variable)

C. null (no value set)

D. Error: variable instance_type not set

Solution

1. Step 1: Understand variable precedence

   Terraform uses environment variables with TF_VAR_ prefix to override default variable values.

2. Step 2: Apply environment variable value

   Since TF_VAR_instance_type is set to "t3.medium", this value overrides the default "t2.micro".

3. Final Answer:

   "t3.medium" (from environment variable) -> Option B

4. Quick Check:

   Environment variable overrides default value [OK]

Hint: Environment variable overrides default Terraform variable [OK]

Common Mistakes:

• Assuming default always applies ignoring environment variable
• Expecting error if environment variable is set
• Confusing null with default value

4. You set the environment variable TF_VAR_count=3 but Terraform still uses the default value count = 1 from the variable declaration. What is the most likely cause?

medium

A. The environment variable name is case-sensitive and should be TF_VAR_Count

B. The environment variable was set after running terraform init

C. The variable count is declared as a string, but environment variable is numeric

D. The shell session where Terraform runs does not have the environment variable exported

Solution

1. Step 1: Check environment variable visibility

   Terraform reads environment variables from the shell session it runs in; if not exported, Terraform won't see it.

2. Step 2: Confirm export of variable

   Setting TF_VAR_count=3 without export means it's not passed to child processes like Terraform.

3. Final Answer:

   The shell session where Terraform runs does not have the environment variable exported -> Option D

4. Quick Check:

   Environment variables must be exported to be visible [OK]

Hint: Always export environment variables before running Terraform [OK]

Common Mistakes:

• Assuming variable names are case-insensitive
• Thinking terraform init caches variable values
• Confusing variable type mismatch as cause

5. You want to securely provide a sensitive variable db_password to Terraform without storing it in code or plain text files. Which approach using environment variables is best practice?

hard

A. Set export TF_VAR_db_password=your_password in your shell before running Terraform

B. Hardcode the password in terraform.tfvars file

C. Use terraform apply -var 'db_password=your_password' every time

D. Store the password in a public GitHub repository and reference it

Solution

1. Step 1: Avoid storing sensitive data in code files

   Hardcoding passwords in files or public repos risks exposure.

2. Step 2: Use environment variables for sensitive data

   Setting TF_VAR_db_password in the shell keeps secrets out of code and version control.

3. Final Answer:

   Set export TF_VAR_db_password=your_password in your shell before running Terraform -> Option A

4. Quick Check:

   Environment variables keep secrets out of code [OK]

Hint: Use TF_VAR_ environment variables to keep secrets out of code [OK]

Common Mistakes:

• Storing secrets in terraform.tfvars files
• Passing secrets on command line risking history leaks
• Publishing secrets in public repositories