Variable validation blocks in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Terraform

variable "region" {
  type = string

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

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

Avar.region == ""

Bvar.region != ""

Cvar.region == null

Dvar.region == 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' causes the validation to fail incorrectly.

Checking for null instead of empty string when the variable is a string.

The validation condition must check that the variable is not an empty string to ensure a value is provided.

2fill in blank

medium

Complete the code to validate that the number variable is greater than zero.

Terraform

variable "instance_count" {
  type = number

  validation {
    condition     = [1]
    error_message = "Instance count must be greater than zero."
  }
}

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

Avar.instance_count > 0

Bvar.instance_count == 0

Cvar.instance_count <= 0

Dvar.instance_count < 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' which would allow zero or negative numbers.

Checking for equality to zero instead of greater than zero.

The condition must ensure the number is greater than zero to be valid.

3fill in blank

hard

Fix the error in the validation condition to check if the string variable is one of allowed values.

Terraform

variable "environment" {
  type = string

  validation {
    condition     = contains(["dev", "staging", "prod"], [1])
    error_message = "Environment must be dev, staging, or prod."
  }
}

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

Aenvironment_var

Bvar.env

Cvar.environment

Denvironment

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable name without 'var.' prefix causes an error.

Using a wrong variable name that does not exist.

The variable must be referenced with 'var.' prefix to access its value inside the validation block.

4fill in blank

hard

Fill both blanks to validate a list variable has at least two items and all are strings.

Terraform

variable "zones" {
  type = list(string)

  validation {
    condition     = length([1]) >= 2 && alltrue([for z in [2] : length(z) > 0])
    error_message = "Zones list must have at least two valid strings."
  }
}

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

Avar.zones

Bzones

Cvar.zone_list

Dzone_list

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable name without 'var.' prefix.

Using different variable names in the two blanks.

Both blanks must reference the variable with 'var.zones' to check its length and iterate over its items.

5fill in blank

hard

Fill all three blanks to validate a map variable keys and values meet conditions.

Terraform

variable "tags" {
  type = map(string)

  validation {
    condition     = alltrue([for k, v in [1] : length(k) > 0 && length(v) [2] 0 && v != [3]])
    error_message = "Tags keys and values must be non-empty strings and values cannot be 'none'."
  }
}

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

Avar.tags

B>

C"none"

Dtags

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable name without 'var.' prefix.

Using wrong comparison operators.

Not quoting the string 'none'.

The condition iterates over 'var.tags', checks keys length > 0, values length > 0, and values not equal to 'none'.

Practice

1. What is the main purpose of a validation block inside a Terraform variable?

easy

A. To check if the input value meets specific rules before applying the configuration

B. To assign a default value to the variable

C. To declare the variable type

D. To output the variable value after deployment

Solution

1. Step 1: Understand variable validation purpose

   The validation block is used to enforce rules on input values to prevent invalid configurations.

2. Step 2: Differentiate from other variable features

   Default values assign fallback values, type declares data type, and output shows results, but validation specifically checks input correctness.

3. Final Answer:

   To check if the input value meets specific rules before applying the configuration -> Option A

4. Quick Check:

   Validation block purpose = input checking [OK]

Hint: Validation blocks check inputs before use [OK]

Common Mistakes:

• Confusing validation with default value assignment
• Thinking validation outputs variable values
• Mixing validation with type declaration

2. Which of the following is the correct syntax to add a validation block inside a Terraform variable?

easy

A. variable "example" { validate { condition = length(var.example) > 0 error = "Must not be empty" } }

B. variable "example" { validation { condition = length(var.example) > 0 error_message = "Must not be empty" } }

C. variable "example" { validation { check = length(var.example) > 0 message = "Must not be empty" } }

D. variable "example" { validation { condition = length(example) > 0 error_message = "Must not be empty" } }

Solution

1. Step 1: Identify correct block and attribute names

   The correct block is validation with attributes condition and error_message.

2. Step 2: Check variable references and syntax

   Inside the condition, use var.example to refer to the variable value. variable "example" { validation { condition = length(var.example) > 0 error_message = "Must not be empty" } } matches this exactly.

3. Final Answer:

   variable "example" { validation { condition = length(var.example) > 0 error_message = "Must not be empty" } } -> Option B

4. Quick Check:

   Validation syntax = correct block and attributes [OK]

Hint: Use 'validation' block with 'condition' and 'error_message' [OK]

Common Mistakes:

• Using 'validate' instead of 'validation'
• Using wrong attribute names like 'check' or 'error'
• Referencing variable without 'var.' prefix

3. Given this variable declaration:

variable "port" {
  type = number
  validation {
    condition     = var.port >= 1024 && var.port <= 65535
    error_message = "Port must be between 1024 and 65535"
  }
}

What happens if you set port = 80 when applying Terraform?

medium

A. Terraform will apply successfully with port 80

B. Terraform will prompt to enter a valid port

C. Terraform will ignore the validation and use default port

D. Terraform will fail with error: Port must be between 1024 and 65535

Solution

1. Step 1: Analyze the validation condition

   The condition requires the port to be between 1024 and 65535 inclusive.

2. Step 2: Check the input value against the condition

   Port 80 is less than 1024, so the condition fails.

3. Step 3: Understand Terraform behavior on validation failure

   Terraform stops and shows the error message from error_message.

4. Final Answer:

   Terraform will fail with error: Port must be between 1024 and 65535 -> Option D

5. Quick Check:

   Validation fails = error message shown [OK]

Hint: Validation blocks stop apply if condition is false [OK]

Common Mistakes:

• Assuming Terraform applies anyway
• Thinking default values are used automatically
• Expecting interactive prompts for invalid input

4. Identify the error in this variable validation block:

variable "env" {
  type = string
  validation {
    condition     = var.env == "dev" || "prod"
    error_message = "env must be 'dev' or 'prod'"
  }
}

medium

A. Validation blocks cannot use logical OR operators

B. The error_message attribute is misspelled

C. The condition syntax is incorrect; it should compare both values explicitly

D. The variable type should be list, not string

Solution

1. Step 1: Review the condition expression

   The condition var.env == "dev" || "prod" is invalid because "prod" alone is always true.

2. Step 2: Correct the condition syntax

   It should be var.env == "dev" || var.env == "prod" to compare both values explicitly.

3. Final Answer:

   The condition syntax is incorrect; it should compare both values explicitly -> Option C

4. Quick Check:

   Logical OR needs full comparisons [OK]

Hint: Use full comparisons on both sides of OR [OK]

Common Mistakes:

• Writing incomplete logical expressions
• Assuming string alone works as condition
• Confusing error_message spelling

5. You want to validate a list variable users so it must have at least 2 unique names and none can be empty strings. Which validation block correctly enforces this?

hard

A. validation { condition = length(var.users) >= 2 && length(distinct(var.users)) == length(var.users) && alltrue([for u in var.users : u != ""]) error_message = "Users must have 2+ unique non-empty names" }

B. validation { condition = length(var.users) > 2 && distinct(var.users) != [] error_message = "Users must have 2+ unique names" }

C. validation { condition = length(var.users) >= 2 && var.users != [""] error_message = "Users must not be empty" }

D. validation { condition = length(var.users) >= 2 && length(var.users) == length(distinct(var.users)) error_message = "Users must have unique names" }

Solution

1. Step 1: Check list length and uniqueness

   Condition requires at least 2 items and all must be unique, so length(var.users) >= 2 and length(distinct(var.users)) == length(var.users) ensure this.

2. Step 2: Ensure no empty strings

   The alltrue([for u in var.users : u != ""]) checks every user is not empty.

3. Step 3: Compare options

   validation { condition = length(var.users) >= 2 && length(distinct(var.users)) == length(var.users) && alltrue([for u in var.users : u != ""]) error_message = "Users must have 2+ unique non-empty names" } includes all these checks correctly; others miss empty string check or uniqueness properly.

4. Final Answer:

   validation { condition = length(var.users) >= 2 && length(distinct(var.users)) == length(var.users) && alltrue([for u in var.users : u != ""]) error_message = "Users must have 2+ unique non-empty names" } -> Option A

5. Quick Check:

   All conditions combined = validation { condition = length(var.users) >= 2 && length(distinct(var.users)) == length(var.users) && alltrue([for u in var.users : u != ""]) error_message = "Users must have 2+ unique non-empty names" } [OK]

Hint: Combine length, distinct, and alltrue for list validation [OK]

Common Mistakes:

• Missing empty string check
• Using > 2 instead of >= 2 for minimum count
• Not verifying uniqueness correctly