Variable validation rules in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a variable with a description.

Terraform

variable "region" {
  type        = string
  description = [1]
}

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

Aaws_region

B"AWS region to deploy resources"

Cstring

Ddefault = "us-east-1"

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable name instead of a description string

Omitting quotes around the description

The description field must be a string describing the variable's purpose.

2fill in blank

medium

Complete the code to add a validation rule that ensures the variable is not empty.

Terraform

variable "environment" {
  type = string

  validation {
    condition     = [1]
    error_message = "Environment cannot be empty."
  }
}

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

Avar.environment == ""

Bvar.environment != null

Clength(var.environment) > 0

Dvar.environment == null

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for equality with empty string instead of length

Using null checks which are not appropriate for strings

The condition checks that the length of the string is greater than zero to ensure it is not empty.

3fill in blank

hard

Fix the error in the validation condition to allow only values 'dev', 'staging', or 'prod'.

Terraform

variable "stage" {
  type = string

  validation {
    condition     = contains([[1]], var.stage)
    error_message = "Stage must be one of: dev, staging, prod."
  }
}

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

A["dev", "staging", "prod"]

B"dev", "staging", "prod"

Cdev, staging, prod

D"dev staging prod"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of a list

Omitting square brackets around the list

The contains function requires a list as the first argument, so the values must be inside square brackets.

4fill in blank

hard

Fill both blanks to validate a number variable is between 1 and 10 inclusive.

Terraform

variable "instance_count" {
  type = number

  validation {
    condition     = var.instance_count [1] 1 && var.instance_count [2] 10
    error_message = "Instance count must be between 1 and 10."
  }
}

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

A>=

B<=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using strict greater than or less than which excludes boundary values

Swapping the operators

The variable must be greater than or equal to 1 and less than or equal to 10.

5fill in blank

hard

Fill all three blanks to validate a list variable contains only allowed strings.

Terraform

variable "allowed_zones" {
  type = list(string)

  validation {
    condition     = alltrue([for zone in var.allowed_zones : zone [1] [[2]]])
    error_message = "Zones must be one of the allowed values."
  }
}

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

Ain

B"us-east-1a", "us-east-1b", "us-east-1c"

Ccontains

D"us-west-2a", "us-west-2b", "us-west-2c"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'contains' incorrectly as an operator instead of a function

Not using a for expression to check each item

Providing the wrong list of zones

The code uses a for expression to check each zone is in the allowed list using the 'in' operator, and alltrue to ensure all pass. The list of allowed zones is provided as the second argument to contains.

Practice

1. What is the main purpose of variable validation rules in Terraform?

easy

A. To speed up the Terraform apply process

B. To automatically fix errors in the Terraform code

C. To create new variables dynamically during runtime

D. To check if input values meet specific conditions before applying configuration

Solution

1. Step 1: Understand variable validation role

   Variable validation rules ensure inputs are correct before Terraform uses them.

2. Step 2: Identify the purpose

   They check conditions and show errors if inputs are invalid, preventing mistakes.

3. Final Answer:

   To check if input values meet specific conditions before applying configuration -> Option D

4. Quick Check:

   Validation checks inputs = C [OK]

Hint: Validation rules check inputs before use to avoid errors [OK]

Common Mistakes:

• Thinking validation fixes errors automatically
• Confusing validation with variable creation
• Assuming validation speeds up apply

2. Which of the following is the correct syntax to add a validation rule for a variable in Terraform?

easy

A. variable "name" { validation { condition = length(var.name) > 3 error_message = "Name too short" } }

B. variable "name" { validate { condition = length(var.name) > 3 message = "Name too short" } }

C. variable "name" { validation_rule { check = length(var.name) > 3 error = "Name too short" } }

D. variable "name" { validate_rule { condition = length(var.name) > 3 error_message = "Name too short" } }

Solution

1. Step 1: Recall Terraform variable validation syntax

   Terraform uses validation block inside variable with condition and error_message.

2. Step 2: Match syntax with options

   variable "name" { validation { condition = length(var.name) > 3 error_message = "Name too short" } } matches correct keywords and structure exactly.

3. Final Answer:

   variable "name" { validation { condition = length(var.name) > 3 error_message = "Name too short" } } -> Option A

4. Quick Check:

   Correct keywords: validation, condition, error_message = A [OK]

Hint: Look for 'validation' block with 'condition' and 'error_message' keys [OK]

Common Mistakes:

• Using 'validate' instead of 'validation'
• Using wrong keys like 'message' or 'error'
• Incorrect block names like 'validation_rule'

3. Given this variable definition, what happens if the input is "ab"?

variable "username" {
  type = string
  validation {
    condition = length(var.username) >= 3
    error_message = "Username must be at least 3 characters"
  }
}

medium

A. Terraform apply ignores the validation and warns only

B. Terraform apply succeeds and uses "ab" as username

C. Terraform apply fails with error: Username must be at least 3 characters

D. Terraform apply replaces "ab" with default username

Solution

1. Step 1: Check validation condition

   The condition requires username length >= 3.

2. Step 2: Evaluate input "ab" length

   "ab" length is 2, which is less than 3, so condition fails.

3. Final Answer:

   Terraform apply fails with error: Username must be at least 3 characters -> Option C

4. Quick Check:

   Input length < 3 triggers error = A [OK]

Hint: Check if input meets condition; if not, apply fails with error [OK]

Common Mistakes:

• Assuming apply succeeds despite validation failure
• Thinking validation only warns, not errors
• Believing default values replace invalid input

4. Identify the error in this variable validation block:

variable "port" {
  type = number
  validation {
    condition = var.port > 0 && var.port < 65536
    error_message = "Port must be between 1 and 65535"
  }
}

medium

A. Using 'number' type instead of 'number' is invalid

B. Validation condition uses 'var.port' instead of 'self'

C. Error message is missing a period at the end

D. Validation block must be outside the variable block

Solution

1. Step 1: Understand validation condition context

   Inside validation, use self to refer to the variable value, not var.port.

2. Step 2: Identify incorrect usage

   The condition incorrectly uses var.port, which is not best practice.

3. Final Answer:

   Validation condition uses 'var.port' instead of 'self' -> Option B

4. Quick Check:

   Use 'self' in validation condition = B [OK]

Hint: Use 'self' to refer to variable value inside validation [OK]

Common Mistakes:

• Using 'var.variable_name' inside validation condition
• Placing validation block outside variable block
• Ignoring syntax errors in condition

5. You want to validate a list variable so it only accepts lists with exactly 3 strings, each at least 2 characters long. Which validation condition is correct?

hard

A. condition = length(self) == 3 && all([for s in self : length(s) >= 2])

B. condition = length(self) == 3 && all([for s in self : s > 2])

C. condition = length(self) == 3 && alltrue([for s in self : s >= 2])

D. condition = length(self) == 3 && alltrue([for s in self : length(s) >= 2])

Solution

1. Step 1: Check list length condition

   We want exactly 3 items, so length(self) == 3 is correct.

2. Step 2: Validate each string length

   Use all() to ensure all elements satisfy length(s) >= 2.

3. Step 3: Identify correct function and condition

   all() is the modern function; alltrue() is legacy.

4. Final Answer:

   condition = length(self) == 3 && all([for s in self : length(s) >= 2]) -> Option A

5. Quick Check:

   Use 'all' with length checks and list length = D [OK]

Hint: Use 'all' function and 'self' for list validation [OK]

Common Mistakes:

• Using 'alltrue' instead of 'all'
• Comparing strings directly to numbers
• Using 's > 2' instead of 'length(s) >= 2'