Arguments and expressions in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Configuration

intermediate

Terraform Expression Output Result

What is the value of the count local value after this Terraform expression is evaluated?

Terraform

variable "environment" {
  default = "prod"
}

variable "instance_count" {
  default = 3
}

locals {
  count = var.environment == "prod" ? var.instance_count * 2 : var.instance_count
}

A 0

B 3

C 6

D null

💡 Hint

Check the condition in the ternary expression and how it affects the count.

Since the environment is 'prod', the condition is true, so the count is instance_count * 2 = 3 * 2 = 6.

❓ service_behavior

intermediate

Terraform Conditional Argument Behavior

Given this Terraform resource snippet, what will be the value of the enable_monitoring argument when var.enable is false?

Terraform

resource "aws_instance" "example" {
  ami           = "ami-123456"
  instance_type = "t2.micro"

  enable_monitoring = var.enable ? true : false
}

A true

B false

C null

D Syntax error

💡 Hint

Look at the ternary expression and the value of var.enable.

Since var.enable is false, the ternary expression evaluates to false, so enable_monitoring is set to false.

❓ Architecture

advanced

Terraform Expression for Dynamic Subnet Selection

Which option correctly uses a Terraform expression to select all subnet IDs from var.subnets where the availability_zone equals var.az?

Terraform

variable "subnets" {
  type = list(object({
    id                = string
    availability_zone = string
  }))
}

variable "az" {
  type = string
}

locals {
  selected_subnets = <EXPRESSION>
}

A [for s in var.subnets : s.id if s.availability_zone == var.az]

B [for s in var.subnets : if s.availability_zone == var.az s.id]

C [for s in var.subnets : s.id where s.availability_zone == var.az]

D [for s in var.subnets : s.id if s.availability_zone = var.az]

💡 Hint

Terraform uses 'for' expressions with 'if' filters after the colon.

Option A correctly uses the syntax: [for item in list : expression if condition]. Other options have syntax errors.

❓ security

advanced

Terraform Sensitive Variable Expression

What will happen if you try to output a sensitive variable directly in Terraform like this?

Terraform

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

output "password" {
  value = var.db_password
}

A Terraform will fail to plan due to sensitive output.

B Terraform will show the password value in the output.

C Terraform will throw a syntax error.

D Terraform will hide the password value and show <sensitive> in the output.

💡 Hint

Sensitive variables are handled specially in outputs.

Terraform masks sensitive output values by showing instead of the actual value.

✅ Best Practice

expert

Terraform Expression for Optional Argument with Default

Which option correctly sets an optional argument tags in a resource to use var.tags if defined, or an empty map if not defined?

Terraform

variable "tags" {
  type    = map(string)
  default = null
}

resource "aws_instance" "example" {
  ami           = "ami-123456"
  instance_type = "t2.micro"

  tags = <EXPRESSION>
}

A var.tags ?? {}

B var.tags ? var.tags : {}

C var.tags || {}

D var.tags != null ? var.tags : {}

💡 Hint

Terraform uses the null-coalescing operator for default values.

Option A uses the null-coalescing operator '??' which returns var.tags if not null, else {}.

Practice

1. What is the purpose of arguments inside a Terraform resource block?

easy

A. To set specific details or properties for the resource

B. To run commands on the resource after creation

C. To define the cloud provider used

D. To store output values from the resource

Solution

1. Step 1: Understand resource blocks

   Resource blocks define cloud resources, and arguments inside them specify details like size or name.

2. Step 2: Identify argument role

   Arguments set the properties that Terraform uses to create or manage the resource.

3. Final Answer:

   To set specific details or properties for the resource -> Option A

4. Quick Check:

   Arguments = resource details [OK]

Hint: Arguments define resource details inside blocks [OK]

Common Mistakes:

• Confusing arguments with outputs
• Thinking arguments run commands
• Mixing provider definition with arguments

2. Which of the following is the correct syntax to assign a variable value to an argument in Terraform?

easy

A. name := var.instance_name

B. name => var.instance_name

C. name == var.instance_name

D. name = var.instance_name

Solution

1. Step 1: Recall Terraform assignment syntax

   Terraform uses single equals sign (=) to assign values to arguments.

2. Step 2: Match variable usage

   Variables are referenced with var.<variable_name> and assigned using =.

3. Final Answer:

   name = var.instance_name -> Option D

4. Quick Check:

   Assignment uses = and var. prefix [OK]

Hint: Use = to assign variables in Terraform [OK]

Common Mistakes:

• Using := or == instead of =
• Confusing arrow => with assignment
• Omitting var. prefix for variables

3. Given the Terraform expression count = var.enable ? 3 : 1 and var.enable = false, what will be the value of count?

medium

A. true

B. 3

C. 1

D. false

Solution

1. Step 1: Understand the ternary expression

   The expression uses a condition: if var.enable is true, count is 3; else count is 1.

2. Step 2: Substitute variable value

   Since var.enable is false, the expression returns the value after the colon, which is 1.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   False condition returns second value [OK]

Hint: Ternary returns value after colon if condition is false [OK]

Common Mistakes:

• Choosing the first value regardless of condition
• Confusing boolean with numeric output
• Ignoring variable value in expression

4. What is wrong with this Terraform argument expression?

size = var.instance_size ? "large" : "small"

assuming var.instance_size is a string variable.

medium

A. Ternary condition requires a boolean, not a string

B. Strings cannot be used in ternary expressions

C. The quotes around "large" and "small" are invalid

D. Variable names cannot be used in expressions

Solution

1. Step 1: Check ternary condition type

   The condition before ? must be boolean (true/false), but var.instance_size is a string.

2. Step 2: Identify type mismatch error

   Using a string as condition causes an error because Terraform expects a boolean expression.

3. Final Answer:

   Ternary condition requires a boolean, not a string -> Option A

4. Quick Check:

   Condition must be boolean [OK]

Hint: Ternary condition must be true/false, not string [OK]

Common Mistakes:

• Using strings as conditions
• Misplacing quotes around values
• Assuming variables can't be in expressions

5. You want to create multiple AWS EC2 instances only if var.create_instances is true. Which expression correctly sets the count argument to 5 when true, or 0 when false?

hard

A. count = var.create_instances == 5

B. count = var.create_instances ? 5 : 0

C. count = var.create_instances && 5

D. count = var.create_instances || 0

Solution

1. Step 1: Understand conditional count setting

   We want count to be 5 if var.create_instances is true, else 0.

2. Step 2: Evaluate each option

   count = var.create_instances ? 5 : 0 uses ternary: if true, 5; else 0. Options B, C, D misuse operators or return booleans.

3. Final Answer:

   count = var.create_instances ? 5 : 0 -> Option B

4. Quick Check:

   Ternary sets count correctly [OK]

Hint: Use ternary to set count based on boolean variable [OK]

Common Mistakes:

• Using boolean expressions instead of numbers for count
• Confusing && and || operators for count
• Not using ternary for conditional count