String interpolation in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to interpolate the variable 'name' inside the string.

Terraform

output "greeting" {
  value = "Hello, ${var.[1]!"
}

Drag options to blanks, or click blank then click option'

Ausername

Buser

Cname

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that does not exist like 'username' or 'user'.

Forgetting to use the 'var.' prefix inside interpolation.

The variable 'name' is referenced as var.name inside the interpolation syntax ${}.

2fill in blank

medium

Complete the code to concatenate the variable 'region' with a string using interpolation.

Terraform

resource "aws_instance" "example" {
  tags = {
    Name = "web-server-[1]"
  }
}

Drag options to blanks, or click blank then click option'

A${var.region}

Bvar.region

C${region}

Dregion

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the interpolation syntax and writing just 'var.region'.

Using the variable name without the 'var.' prefix.

To interpolate a variable in Terraform, use ${var.variable_name}. Here, ${var.region} correctly inserts the region value.

3fill in blank

hard

Fix the error in the interpolation syntax to correctly reference the 'environment' variable.

Terraform

output "env_name" {
  value = "Current environment is ${var.[1]"
}

Drag options to blanks, or click blank then click option'

Aenvironment}

Benvironment

Cenvironment}}

D{environment}

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving out the closing brace '}' in the interpolation.

Adding extra braces or missing the variable prefix.

The interpolation syntax must be closed properly with a closing brace }. The correct reference is ${var.environment}.

4fill in blank

hard

Fill both blanks to create a tag that combines 'app' and 'version' variables with a dash.

Terraform

resource "aws_s3_bucket" "bucket" {
  tags = {
    Name = "${var.[1]-${var.[2]"
  }
}

Drag options to blanks, or click blank then click option'

Aapp

Bversion

Cenv

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using variables that do not exist like 'env' or 'name'.

Forgetting to use the 'var.' prefix.

The tag combines the 'app' and 'version' variables separated by a dash. Both variables must be referenced with var. inside interpolation.

5fill in blank

hard

Fill all three blanks to create an output that shows the full resource ID with region and environment.

Terraform

output "resource_id" {
  value = "arn:aws:ec2:${var.[1]:${var.[2]:instance/${var.[3]"
}

Drag options to blanks, or click blank then click option'

Aregion

Baccount_id

Cinstance_id

Denvironment

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up variable names or missing the 'var.' prefix.

Using 'environment' instead of 'account_id' or 'instance_id'.

The ARN format requires region, account ID, and instance ID. Each variable is referenced with var. inside interpolation.

Practice

1. What does string interpolation in Terraform do?
${} is used to:

easy

A. Create new variables automatically

B. Insert variable or expression values inside strings

C. Comment out lines in configuration

D. Encrypt sensitive data in strings

Solution

1. Step 1: Understand string interpolation syntax

   Terraform uses ${} inside double quotes to insert values dynamically into strings.

2. Step 2: Identify the purpose of interpolation

   This allows combining text with variable or expression results to build flexible strings.

3. Final Answer:

   Insert variable or expression values inside strings -> Option B

4. Quick Check:

   String interpolation = Insert values [OK]

Hint: Remember ${} inserts values inside strings [OK]

Common Mistakes:

• Thinking it creates variables
• Confusing with comments
• Assuming it encrypts data

2. Which of the following is the correct syntax for string interpolation in Terraform?

easy

A. 'Hello, $var.name!'

B. 'Hello, ${var.name}!'

C. "Hello, ${var.name}!"

D. "Hello, $var.name!"

Solution

1. Step 1: Check string quoting rules

   Terraform requires double quotes for strings with interpolation; single quotes treat content literally.

2. Step 2: Verify interpolation syntax

   The correct interpolation uses ${} inside double quotes to evaluate expressions.

3. Final Answer:

   "Hello, ${var.name}!" -> Option C

4. Quick Check:

   Double quotes + ${} = correct syntax [OK]

Hint: Use double quotes with ${} for interpolation [OK]

Common Mistakes:

• Using single quotes which disable interpolation
• Missing curly braces around variable
• Using $ without braces

3. Given the Terraform code:

variable "env" { default = "prod" }
output "message" {
  value = "Deploying to ${var.env} environment"
}

What will be the output value?

medium

A. Deploying to prod environment

B. Deploying to ${var.env} environment

C. Deploying to env environment

D. Syntax error

Solution

1. Step 1: Identify variable value

   The variable env has default value "prod".

2. Step 2: Evaluate interpolation in output

   The string uses ${var.env} which inserts "prod" into the string.

3. Final Answer:

   Deploying to prod environment -> Option A

4. Quick Check:

   Interpolation replaces var.env with prod [OK]

Hint: Interpolation replaces variables with their values [OK]

Common Mistakes:

• Thinking interpolation shows literal text
• Confusing variable name with value
• Assuming syntax error due to quotes

4. What is wrong with this Terraform string interpolation?

output "example" {
  value = "Path is ${path}"  
}

Assuming path is not defined anywhere.

medium

A. Interpolation ignored, outputs empty string

B. Syntax error due to missing variable declaration

C. No error, outputs literal string

D. Runtime error: undefined variable 'path'

Solution

1. Step 1: Check variable usage

   The interpolation uses ${path} but path is not declared as a variable or local.

2. Step 2: Understand Terraform behavior

   Terraform throws a runtime error when a referenced variable is undefined.

3. Final Answer:

   Runtime error: undefined variable 'path' -> Option D

4. Quick Check:

   Undefined variable causes runtime error [OK]

Hint: Undefined variables cause runtime errors in interpolation [OK]

Common Mistakes:

• Assuming no error and literal output
• Thinking it's a syntax error
• Expecting empty string output

5. You want to create a resource name that combines environment and region variables in Terraform. Which interpolation correctly creates a name like app-prod-uswest?

variable "env" { default = "prod" }
variable "region" { default = "uswest" }

hard

A. "app-${var.env}-${var.region}"

B. "app-${env}-${region}"

C. "app-${var.env + var.region}"

D. "app-${var.env}_${var.region}"

Solution

1. Step 1: Use correct variable references

   Variables must be referenced as var.env and var.region inside interpolation.

2. Step 2: Combine with dashes correctly

   Use string interpolation with dashes between variables: "app-${var.env}-${var.region}".

3. Final Answer:

   "app-${var.env}-${var.region}" -> Option A

4. Quick Check:

   Correct variable syntax + dashes = "app-${var.env}-${var.region}" [OK]

Hint: Use var. prefix and separate with dashes inside ${} [OK]

Common Mistakes:

• Omitting var. prefix
• Concatenating without separator
• Using underscore instead of dash