Sensitive variable handling in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a sensitive variable in Terraform?

A sensitive variable is a variable that contains confidential information, such as passwords or API keys, which Terraform hides in its output to protect the data.

beginner

How do you declare a sensitive variable in Terraform?

You declare a sensitive variable by adding the attribute sensitive = true in the variable block.

intermediate

Why should you mark variables as sensitive in Terraform?

Marking variables as sensitive prevents Terraform from showing their values in logs and plan output, reducing the risk of exposing secrets. However, sensitive values are still stored in the state file in plain text.

intermediate

Can sensitive variables be used in Terraform outputs?

Yes, but you must mark the output as sensitive too. Otherwise, Terraform will warn you and may expose the value.

beginner

What happens if you do not mark a secret as sensitive in Terraform?

The secret may appear in Terraform plan, apply logs, or state files, risking accidental exposure to anyone with access to those files.

How do you mark a variable as sensitive in Terraform?

A Add <code>sensitive = true</code> in the variable block

B Prefix the variable name with 'secret_'

C Use <code>private = true</code> in the variable block

D Encrypt the variable value manually

You mark a variable as sensitive by adding sensitive = true in its declaration block.

What does Terraform do with sensitive variables during plan and apply?

A Hides their values in output and logs

B Prints their values in plain text

C Deletes the variables after use

D Saves them in a separate file

Terraform hides sensitive variable values in plan and apply outputs to protect secrets.

If you output a sensitive variable without marking the output as sensitive, what happens?

A Terraform automatically hides the output

B Terraform warns and may expose the value

C Terraform blocks the deployment

D Terraform encrypts the output

Terraform warns you and may expose the sensitive value if the output is not marked sensitive.

Why is it important to mark variables as sensitive?

A To enable variable reuse

B To speed up Terraform runs

C To reduce variable size

D To prevent accidental exposure of secrets in logs and state files

Marking variables sensitive protects secrets from being shown in logs and state files.

Which of the following is NOT a best practice for handling sensitive variables in Terraform?

A Mark variables as sensitive

B Use environment variables or secret managers

C Store secrets in version control in plain text

D Mark outputs as sensitive when they expose secrets

Storing secrets in plain text in version control is unsafe and not recommended.

Explain how to declare and use sensitive variables in Terraform and why it matters.

Think about how Terraform treats secrets differently to keep them safe.

Describe the risks of not marking sensitive variables properly in Terraform.

Consider what happens if anyone can see your Terraform logs or state files.

Practice

1. What does setting sensitive = true on a Terraform variable do?

easy

A. It hides the variable's value in Terraform plan and apply outputs.

B. It encrypts the variable value in the Terraform state file.

C. It makes the variable read-only in the configuration.

D. It automatically rotates the variable value periodically.

Solution

1. Step 1: Understand the purpose of sensitive attribute

   The sensitive = true flag tells Terraform to hide the variable's value in output logs and plans to avoid accidental exposure.

2. Step 2: Clarify what it does not do

   It does not encrypt the state file or rotate values; those are separate concerns.

3. Final Answer:

   It hides the variable's value in Terraform plan and apply outputs. -> Option A

4. Quick Check:

   sensitive = true hides output values [OK]

Hint: Sensitive true hides values in output, not encryption [OK]

Common Mistakes:

• Thinking sensitive encrypts the state file
• Assuming sensitive makes variables read-only
• Believing sensitive rotates secrets automatically

2. Which of the following is the correct syntax to declare a sensitive variable in Terraform?

easy

A. variable "db_password" { type = string sensitive = true }

B. variable "db_password" { type = string
sensitive = true }

C. variable "db_password" { type = string, sensitive = true }

D. variable "db_password" { type = string; sensitive = true }

Solution

1. Step 1: Recall Terraform block syntax

   Terraform uses HCL syntax where attributes inside blocks are separated by new lines without commas or semicolons.

2. Step 2: Identify correct formatting

   variable "db_password" { type = string sensitive = true } correctly places sensitive = true on a new line without commas or semicolons.

3. Final Answer:

   variable "db_password" { type = string sensitive = true } -> Option B

4. Quick Check:

   HCL uses new lines, no commas or semicolons [OK]

Hint: Use new lines, no commas or semicolons in variable blocks [OK]

Common Mistakes:

• Adding commas between attributes
• Using semicolons inside blocks
• Putting attributes on the same line without proper syntax

3. Given this Terraform output block:

output "db_password" {
  value     = var.db_password
  sensitive = true
}

What will Terraform display when you run terraform output?

medium

A. It will show (sensitive) instead of the password.

B. It will cause an error because outputs cannot be sensitive.

C. It will show the actual password value.

D. It will show an empty string.

Solution

1. Step 1: Understand sensitive outputs behavior

   When an output is marked sensitive, Terraform hides its value in the output command to avoid exposing secrets.

2. Step 2: Confirm expected output

   Terraform replaces the actual value with (sensitive) text instead of showing the secret.

3. Final Answer:

   It will show (sensitive) instead of the password. -> Option A

4. Quick Check:

   sensitive output hides value with (sensitive) [OK]

Hint: Sensitive outputs show (sensitive), not actual values [OK]

Common Mistakes:

• Expecting actual secret to print
• Thinking sensitive outputs cause errors
• Assuming output is empty string

4. You have marked a variable as sensitive = true but when running terraform plan, the secret value still appears. What is the most likely cause?

medium

A. You forgot to run terraform apply first.

B. Terraform does not support sensitive variables in plans.

C. The variable is used directly in a resource argument that prints its value.

D. The variable type is not set to string.

Solution

1. Step 1: Understand sensitive variable behavior in plans

   Terraform hides sensitive variable values in outputs but if the variable is interpolated directly into resource arguments that display in plan, the value can appear.

2. Step 2: Identify cause of exposure

   Using sensitive variables in resource arguments that Terraform shows in plan can reveal the secret despite the sensitive flag.

3. Final Answer:

   The variable is used directly in a resource argument that prints its value. -> Option C

4. Quick Check:

   Direct use in resource can expose sensitive values [OK]

Hint: Sensitive hides output but not direct resource interpolation [OK]

Common Mistakes:

• Assuming sensitive hides all plan values
• Thinking apply is needed to hide values
• Believing variable type affects sensitivity

5. You want to securely store a database password in Terraform and avoid exposing it in state files or outputs. Which combination of practices is best?

hard

A. Use sensitive = false and rely on Terraform's default security.

B. Mark the variable as sensitive = true and print it in outputs for verification.

C. Store the password in plain text variable and restrict access to the Terraform config files.

D. Mark the variable as sensitive = true, use sensitive outputs, and encrypt the Terraform state file.

Solution

1. Step 1: Protect variable visibility

   Marking the variable as sensitive hides it in outputs and plans, reducing accidental exposure.

2. Step 2: Secure outputs and state file

   Using sensitive outputs keeps secrets hidden when showing results, and encrypting the state file protects stored secrets.

3. Final Answer:

   Mark the variable as sensitive = true, use sensitive outputs, and encrypt the Terraform state file. -> Option D

4. Quick Check:

   Combine sensitive flag, outputs, and state encryption [OK]

Hint: Combine sensitive flag, outputs, and state encryption [OK]

Common Mistakes:

• Printing sensitive variables in outputs
• Storing secrets in plain text variables
• Relying on defaults without encryption