Sensitive variable handling in Terraform - Mini Project: Build & Apply

Sensitive variable handling

📖 Scenario: You are setting up a Terraform configuration to manage cloud infrastructure. Some variables, like passwords or API keys, must be kept secret to protect your system.

🎯 Goal: Create a Terraform variable marked as sensitive and use it in a resource without exposing its value in outputs.

📋 What You'll Learn

Define a Terraform variable named db_password with type string and mark it as sensitive = true.

Create a resource aws_db_instance named example that uses the db_password variable for its password attribute.

Do not output the db_password variable value directly.

💡 Why This Matters

🌍 Real World

Sensitive variables like passwords and API keys must be protected in infrastructure code to prevent leaks and security risks.

💼 Career

Cloud engineers and DevOps professionals must manage secrets securely in Terraform to maintain compliance and protect infrastructure.

1

Define the sensitive variable

Create a Terraform variable named db_password with type string and set sensitive = true.

Terraform

# Define the sensitive variable db_password
# Your code here

Hint

Use the variable block with sensitive = true to keep the value secret.

2

Add AWS DB instance resource

Add a resource block for aws_db_instance named example and set its password attribute to var.db_password.

Terraform

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

# Add aws_db_instance resource named example
# Your code here

Hint

Use var.db_password to reference the sensitive variable inside the resource.

3

Add a non-sensitive output

Create an output named db_instance_id that outputs aws_db_instance.example.id without exposing the password.

Terraform

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

resource "aws_db_instance" "example" {
  allocated_storage    = 20
  engine               = "mysql"
  instance_class       = "db.t2.micro"
  name                 = "mydb"
  username             = "admin"
  password             = var.db_password
  parameter_group_name = "default.mysql5.7"
}

# Add output for db_instance_id
# Your code here

Hint

Outputs should not reveal sensitive data. Output the instance ID instead of the password.

4

Add a sensitive output for password

Add an output named db_password_output that outputs var.db_password and mark it as sensitive = true.

Terraform

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

resource "aws_db_instance" "example" {
  allocated_storage    = 20
  engine               = "mysql"
  instance_class       = "db.t2.micro"
  name                 = "mydb"
  username             = "admin"
  password             = var.db_password
  parameter_group_name = "default.mysql5.7"
}

output "db_instance_id" {
  value = aws_db_instance.example.id
}

# Add sensitive output for db_password
# Your code here

Hint

Mark the output as sensitive to avoid showing the password in plain text.

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