Check blocks for assertions in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a check block that asserts the instance type is t2.micro.

Terraform

resource "aws_instance" "example" {
  instance_type = "t2.micro"

  [1] {
    condition     = var.instance_type == "t2.micro"
    error_message = "Instance type must be t2.micro"
  }
}

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

Aassert

Bcheck_block

Ccheck

Dverify

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'assert' or 'verify' instead of 'check' causes syntax errors.

Forgetting to include the check block inside the resource.

The correct keyword to define a check block in Terraform is check. This block allows you to assert conditions on resource attributes.

2fill in blank

medium

Complete the code to assert that the AMI ID is not empty in the check block.

Terraform

resource "aws_instance" "example" {
  ami           = var.ami_id
  instance_type = "t2.micro"

  check {
    condition     = [1]
    error_message = "AMI ID must not be empty"
  }
}

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

Avar.ami_id != ""

Bvar.ami_id > ""

Cvar.ami_id = ""

Dvar.ami_id == ""

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment operator '=' instead of comparison.

Checking for equality to empty string instead of inequality.

The condition should check that var.ami_id is not an empty string using != "".

3fill in blank

hard

Fix the error in the check block condition to correctly assert that the count is greater than zero.

Terraform

resource "aws_instance" "example" {
  count         = var.instance_count
  instance_type = "t2.micro"

  check {
    condition     = var.instance_count [1] 0
    error_message = "Instance count must be greater than zero"
  }
}

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

A>

B==

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' or '<' which allow zero or negative values.

Using '==' which only allows exactly zero.

The condition should assert that var.instance_count is greater than zero using the '>' operator.

4fill in blank

hard

Fill both blanks to assert that the environment variable is either 'dev' or 'prod'.

Terraform

variable "environment" {
  type = string
}

resource "aws_instance" "example" {
  instance_type = "t2.micro"

  check {
    condition     = var.environment [1] ["dev", "prod"]
    error_message = "Environment must be 'dev' or 'prod'"
  }
}

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

A!=

B==

Cnot in

Din

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which compares to the whole list, causing errors.

Using 'not in' which negates the condition.

The correct operator to check if a value is inside a list is in. The blank uses 'in' to form the condition.

5fill in blank

hard

Fill all three blanks to assert that the tag 'Name' exists and is not empty.

Terraform

resource "aws_instance" "example" {
  tags = {
    Name = var.instance_name
  }

  check {
    condition     = contains(keys(var.tags), [1]) && var.tags[[2]] [3] ""
    error_message = "Tag 'Name' must exist and not be empty"
  }
}

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

A"Name"

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' to check for non-empty value.

Forgetting to quote the key name 'Name'.

The condition checks if the key 'Name' exists in the tags and that its value is not empty. So, the key name is 'Name' and the operator is '!='.

Practice

1. What is the main purpose of a check block in Terraform?

easy

A. To define variables for resource configuration

B. To verify conditions before resource creation and prevent errors

C. To output resource attributes after deployment

D. To create loops for multiple resource instances

Solution

1. Step 1: Understand the role of check blocks

   Check blocks are used to verify conditions before Terraform creates resources to avoid invalid configurations.

2. Step 2: Differentiate from other blocks

   Variables define inputs, outputs show results, and loops create multiple resources; none verify conditions before creation.

3. Final Answer:

   To verify conditions before resource creation and prevent errors -> Option B

4. Quick Check:

   Check blocks = pre-creation validation [OK]

Hint: Check blocks catch errors before deployment [OK]

Common Mistakes:

• Confusing check blocks with variable declarations
• Thinking check blocks output values
• Assuming check blocks create resources

2. Which of the following is the correct syntax for a check block in Terraform?

easy

A. check "valid_region" { condition var.region == "us-east-1" error_message "Region must be us-east-1" }

B. check "valid_region" { assert = var.region == "us-east-1" message = "Region must be us-east-1" }

C. check "valid_region" { condition = var.region = "us-east-1" error = "Region must be us-east-1" }

D. check "valid_region" { condition = var.region == "us-east-1" error_message = "Region must be us-east-1" }

Solution

1. Step 1: Identify correct attribute names

   The correct syntax uses condition for the boolean check and error_message for the error text.

2. Step 2: Check syntax correctness

   check "valid_region" { condition = var.region == "us-east-1" error_message = "Region must be us-east-1" } correctly uses condition = and error_message = with proper equality ==. Others use wrong attribute names or syntax errors.

3. Final Answer:

   check "valid_region" { condition = var.region == "us-east-1" error_message = "Region must be us-east-1" } -> Option D

4. Quick Check:

   Use condition and error_message with equals signs [OK]

Hint: Use 'condition =' and 'error_message =' inside check blocks [OK]

Common Mistakes:

• Using single equals (=) instead of double equals (==) for condition
• Using wrong attribute names like assert or error
• Missing equals signs between keys and values

3. Given this Terraform snippet:

variable "count" { type = number default = 3 }
check "positive_count" { condition = var.count > 0 error_message = "Count must be positive" }

What happens if you set count = 0 and run terraform apply?

medium

A. Terraform fails with error: Count must be positive

B. Terraform applies resources with count 0, creating none

C. Terraform ignores the check block and applies resources

D. Terraform applies resources but warns about count

Solution

1. Step 1: Understand the check block condition

   The check block requires var.count > 0. Setting count = 0 violates this condition.

2. Step 2: Predict Terraform behavior on violation

   Terraform stops and shows the error message from the check block instead of applying resources.

3. Final Answer:

   Terraform fails with error: Count must be positive -> Option A

4. Quick Check:

   Check blocks stop apply if condition false [OK]

Hint: Check blocks block apply if condition is false [OK]

Common Mistakes:

• Thinking Terraform ignores check blocks
• Assuming resources apply with warnings
• Confusing default variable values with overrides

4. This Terraform check block causes an error during plan:

check "valid_name" { condition = var.name != "" error_message = "Name cannot be empty" }

What is the likely cause if var.name is not set?

medium

A. Terraform errors because var.name is null and comparison fails

B. Terraform ignores the check block if variable is unset

C. Terraform treats unset variable as empty string and passes check

D. Terraform applies default empty string and shows warning only

Solution

1. Step 1: Analyze variable unset behavior

   If var.name is not set and has no default, it is null, not an empty string.

2. Step 2: Understand condition evaluation

   Comparing null to empty string with != causes an error because null is not a string.

3. Final Answer:

   Terraform errors because var.name is null and comparison fails -> Option A

4. Quick Check:

   Null variables cause check block errors if compared to strings [OK]

Hint: Unset variables are null, not empty strings [OK]

Common Mistakes:

• Assuming unset variables default to empty strings
• Expecting check blocks to ignore null values
• Thinking Terraform only warns on check failures

5. You want to enforce that a variable region is either "us-east-1" or "us-west-2" using a check block. Which is the correct check block to enforce this?

hard

A. check "valid_region" { condition = var.region == "us-east-1" || var.region == "us-west-2" error_message = "Region must be us-east-1 or us-west-2" }

B. check "valid_region" { condition = var.region == ["us-east-1", "us-west-2"] error_message = "Region must be us-east-1 or us-west-2" }

C. check "valid_region" { condition = contains(["us-east-1", "us-west-2"], var.region) error_message = "Region must be us-east-1 or us-west-2" }

D. check "valid_region" { condition = var.region in ("us-east-1", "us-west-2") error_message = "Region must be us-east-1 or us-west-2" }

Solution

1. Step 1: Understand how to check membership in a list

   Terraform uses the contains(list, value) function to check if a value is in a list.

2. Step 2: Evaluate each option

   check "valid_region" { condition = var.region == "us-east-1" || var.region == "us-west-2" error_message = "Region must be us-east-1 or us-west-2" } uses logical OR correctly but is verbose; check "valid_region" { condition = var.region == ["us-east-1", "us-west-2"] error_message = "Region must be us-east-1 or us-west-2" } compares a string to a list incorrectly; check "valid_region" { condition = contains(["us-east-1", "us-west-2"], var.region) error_message = "Region must be us-east-1 or us-west-2" } uses contains properly; check "valid_region" { condition = var.region in ("us-east-1", "us-west-2") error_message = "Region must be us-east-1 or us-west-2" } uses invalid syntax in.

3. Final Answer:

   check "valid_region" { condition = contains(["us-east-1", "us-west-2"], var.region) error_message = "Region must be us-east-1 or us-west-2" } -> Option C

4. Quick Check:

   Use contains(list, value) to check membership [OK]

Hint: Use contains() to check if value is in list [OK]

Common Mistakes:

• Using 'in' keyword which Terraform does not support
• Comparing string directly to list
• Using verbose OR instead of contains()