Environment variables (TF_VAR_) in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of environment variables prefixed with TF_VAR_ in Terraform?

They allow you to set Terraform input variables outside of configuration files, making it easier to manage sensitive or environment-specific values.

beginner

How does Terraform use an environment variable named TF_VAR_region?

Terraform automatically maps TF_VAR_region to the input variable named region in your Terraform configuration.

intermediate

Why might you prefer using TF_VAR_ environment variables over hardcoding variables in Terraform files?

Using TF_VAR_ environment variables keeps sensitive data out of code, supports different environments easily, and avoids committing secrets to version control.

intermediate

Can you use TF_VAR_ environment variables to set complex types like lists or maps in Terraform?

Yes, but you must provide the value as a JSON string that Terraform can parse into the complex type.

intermediate

What happens if both a Terraform variable file and a TF_VAR_ environment variable set the same variable?

The TF_VAR_ environment variable takes precedence over the variable file value.

What prefix must an environment variable have to be recognized by Terraform as an input variable?

A TERRAFORM_VAR_

B TF_VAR_

C TF_INPUT_

D VAR_

Terraform recognizes environment variables starting with TF_VAR_ as input variables.

How should you format a list variable when setting it via a TF_VAR_ environment variable?

A Comma-separated string without quotes

B Plain string with brackets

C Space-separated string

D JSON string representing the list

Terraform expects complex types like lists to be passed as JSON strings in TF_VAR_ environment variables.

If you set a variable in both a .tfvars file and a TF_VAR_ environment variable, which one does Terraform use?

A TF_VAR_ environment variable value

B .tfvars file value

C The first one declared in the configuration

D Terraform throws an error

TF_VAR_ environment variables override values set in .tfvars files.

Why is using TF_VAR_ environment variables considered a best practice for sensitive data?

A Because they encrypt the data automatically

B Because they are easier to type

C Because they keep sensitive data out of code and version control

D Because Terraform ignores them in logs

Using environment variables avoids storing secrets in code or version control systems.

Which of the following is a valid TF_VAR_ environment variable for a Terraform variable named 'password'?

A TF_VAR_password=MySecret123

B TF_VAR_password='MySecret123'

C TF_VAR_password:MySecret123

D TF_VAR_password MySecret123

The correct syntax is TF_VAR_variableName=value without quotes or special characters.

Explain how Terraform uses environment variables prefixed with TF_VAR_ to set input variables.

Think about how environment variables can replace or override variable files.

Describe best practices and benefits of using TF_VAR_ environment variables in Terraform projects.

Consider security and flexibility advantages.

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