Conditional expressions (ternary) in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Terraform Conditional Expression Output

What will be the value of instance_type after applying this Terraform configuration snippet?

Terraform

variable "environment" {
  default = "production"
}

locals {
  instance_type = var.environment == "production" ? "t3.large" : "t3.micro"
}

A "t3.large"

B "t3.micro"

C "production"

D null

💡 Hint

Check the condition comparing the environment variable.

The condition checks if environment equals "production". Since it does, the instance_type is set to "t3.large".

❓ Configuration

intermediate

Terraform Conditional Expression in Resource Count

Given the following Terraform resource snippet, how many instances of aws_instance will be created if var.deploy is false?

Terraform

variable "deploy" {
  default = false
}

resource "aws_instance" "example" {
  count = var.deploy ? 3 : 0
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A 0

B 1

C 3

D Error: count must be a positive integer

💡 Hint

Look at the count expression and the value of var.deploy.

Since var.deploy is false, the count expression evaluates to 0, so no instances are created.

❓ Architecture

advanced

Choosing Subnet Based on Environment Using Conditional Expression

In a Terraform module, you want to select a subnet ID based on the environment variable var.env. Which option correctly assigns subnet_id to "subnet-prod123" if var.env is "prod", and to "subnet-dev123" otherwise?

A subnet_id = var.env ? "subnet-prod123" : "subnet-dev123"

B subnet_id = var.env == "prod" ? "subnet-dev123" : "subnet-prod123"

C subnet_id = var.env == "prod" ? "subnet-prod123" : "subnet-dev123"

D subnet_id = var.env = "prod" ? "subnet-prod123" : "subnet-dev123"

💡 Hint

Check the equality operator and the order of values in the ternary expression.

Option C correctly uses the equality operator == and assigns the prod subnet when var.env is "prod".

❓ security

advanced

Conditional Expression for Enabling Encryption

You want to enable encryption on an AWS S3 bucket only if the variable var.enable_encryption is true. Which Terraform snippet correctly sets the server_side_encryption_configuration block conditionally?

A server_side_encryption_configuration = var.enable_encryption ? [] : [{ rule: { apply_server_side_encryption_by_default: { sse_algorithm: "AES256" } } }]

B server_side_encryption_configuration = var.enable_encryption ? [{ rule: { apply_server_side_encryption_by_default: { sse_algorithm: "AES256" } } }] : []

C server_side_encryption_configuration = var.enable_encryption == true ? [] : null

D server_side_encryption_configuration = var.enable_encryption ? null : [{ rule: { apply_server_side_encryption_by_default: { sse_algorithm: "AES256" } } }]

💡 Hint

Encryption block should be present only when enabled.

Option B correctly assigns the encryption configuration when var.enable_encryption is true, otherwise an empty list disables it.

✅ Best Practice

expert

Complex Conditional Expression for Instance Count

Consider this Terraform variable and resource snippet. What is the value of count for aws_instance.example if var.env is "staging" and var.scale_up is true?

Terraform

variable "env" {
  default = "staging"
}

variable "scale_up" {
  default = true
}

resource "aws_instance" "example" {
  count = var.env == "production" ? 5 : (var.scale_up ? 3 : 1)
  ami           = "ami-abc123"
  instance_type = "t3.medium"
}

A 0

B 5

C 1

D 3

💡 Hint

Evaluate the nested conditional expression step by step.

Since var.env is not "production", the count depends on var.scale_up. Because var.scale_up is true, count is 3.

Practice

1. What does this Terraform conditional expression do?
var.is_production ? "prod" : "dev"

easy

A. Returns true or false

B. Always returns "prod"

C. Returns "prod" if var.is_production is true, otherwise "dev"

D. Causes a syntax error

Solution

1. Step 1: Understand the condition

   The expression checks if var.is_production is true or false.

2. Step 2: Evaluate the ternary expression

   If true, it returns "prod"; if false, it returns "dev".

3. Final Answer:

   Returns "prod" if var.is_production is true, otherwise "dev" -> Option C

4. Quick Check:

   Condition ? true_value : false_value = C [OK]

Hint: Remember: condition ? value_if_true : value_if_false [OK]

Common Mistakes:

• Thinking it returns a boolean
• Confusing true and false branches
• Assuming it always returns the first value

2. Which of these is the correct syntax for a Terraform conditional expression?

easy

A. condition : true_val ? false_val

B. condition ? true_val : false_val

C. condition ? (true_val, false_val)

D. if (condition) then true_val else false_val

Solution

1. Step 1: Recall Terraform conditional syntax

   Terraform uses the format: condition ? true_val : false_val.

2. Step 2: Compare options

   Only condition ? true_val : false_val matches this syntax exactly.

3. Final Answer:

   condition ? true_val : false_val -> Option B

4. Quick Check:

   Correct ternary syntax = D [OK]

Hint: Look for question mark and colon in correct order [OK]

Common Mistakes:

• Using if-then-else syntax from other languages
• Swapping question mark and colon
• Using commas inside the expression

3. Given this Terraform code:

variable "env" { default = "test" }
output "message" {
  value = var.env == "prod" ? "Deploy to production" : "Deploy to staging"
}

What will be the output value?

medium

A. Error: unknown variable

B. "Deploy to production"

C. "test"

D. "Deploy to staging"

Solution

1. Step 1: Check variable value

   var.env is set to "test" by default.

2. Step 2: Evaluate condition

   var.env == "prod" is false, so the false branch "Deploy to staging" is chosen.

3. Final Answer:

   "Deploy to staging" -> Option D

4. Quick Check:

   Condition false -> false branch output = A [OK]

Hint: Check variable value before condition evaluation [OK]

Common Mistakes:

• Assuming default is "prod"
• Confusing true and false branches
• Expecting variable value as output

4. Identify the error in this Terraform conditional expression:

output "result" {
  value = var.enabled ? "yes" "no"
}

medium

A. Missing colon ':' between true and false values

B. Variable var.enabled is undefined

C. Quotes around values are incorrect

D. Ternary operator not supported in outputs

Solution

1. Step 1: Review ternary syntax

   The correct syntax requires a colon ':' between true and false values.

2. Step 2: Identify missing colon

   The expression has "? \"yes\" \"no\"" missing the ':' separator.

3. Final Answer:

   Missing colon ':' between true and false values -> Option A

4. Quick Check:

   Syntax error due to missing ':' = A [OK]

Hint: Check for '?' and ':' pair in ternary expressions [OK]

Common Mistakes:

• Omitting the colon ':'
• Misplacing quotes
• Assuming ternary not allowed in outputs

5. You want to assign a resource name based on environment, but if the environment variable is empty or null, use "default" instead. Which expression correctly does this in Terraform?

var.env == "" || var.env == null ? "default" : var.env

hard

A. var.env == "" || var.env == null ? "default" : var.env

B. var.env == "" && var.env == null ? "default" : var.env

C. var.env ? "default" : var.env

D. var.env == null ? var.env : "default"

Solution

1. Step 1: Understand the requirement

   If var.env is empty string or null, use "default"; else use var.env.

2. Step 2: Analyze each option

   var.env == "" || var.env == null ? "default" : var.env checks if var.env is empty or null, then returns "default", else var.env, matching the requirement exactly.

3. Final Answer:

   var.env == "" || var.env == null ? "default" : var.env -> Option A

4. Quick Check:

   Check empty or null -> default else env = B [OK]

Hint: Check both empty string and null explicitly in condition [OK]

Common Mistakes:

• Using && instead of || causing wrong logic
• Assuming var.env alone checks for empty or null
• Swapping true and false branches