Null values handling in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Handling null values in Terraform variables

Given the following Terraform variable declaration and usage, what will be the value of resource_name after applying the configuration if var.name is null?

Terraform

variable "name" {
  type    = string
  default = null
}

locals {
  resource_name = var.name != null ? var.name : "default-name"
}

A null

B "default-name"

C ""

D Error: variable "name" must not be null

💡 Hint

Check how the ternary operator handles null values in Terraform.

The local variable resource_name uses a conditional expression to check if var.name is not null. If it is null, it assigns "default-name". Since var.name is null, the result is "default-name".

❓ Configuration

intermediate

Null value in Terraform map lookup

What will be the output of the following Terraform expression if var.settings is {} (an empty map)?

Terraform

variable "settings" {
  type = map(string)
  default = {}
}

output "region" {
  value = lookup(var.settings, "region", null)
}

A null

B "region"

C Error: key "region" not found

D ""

💡 Hint

The lookup function returns the default value if the key is missing.

The lookup function returns the value for the key if it exists. If not, it returns the default value provided, which is null here. Since the map is empty, the output is null.

❓ Architecture

advanced

Impact of null values on resource count in Terraform

Consider the following Terraform snippet. What will be the number of aws_instance resources created if var.instance_count is null?

Terraform

variable "instance_count" {
  type    = number
  default = null
}

resource "aws_instance" "example" {
  count = var.instance_count != null ? var.instance_count : 1
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A 1

B 0

C null

D Error: count must be a non-negative integer

💡 Hint

Look at how the count argument handles null values with a conditional expression.

The count argument uses a conditional expression to assign 1 if var.instance_count is null. Since it is null, count becomes 1, so one instance is created.

❓ security

advanced

Null values in sensitive Terraform variables

If a sensitive Terraform variable is set to null, what is the behavior when it is used in a resource attribute expecting a string?

Terraform

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

resource "aws_db_instance" "default" {
  password = var.db_password
  # other required attributes
}

A Terraform ignores the password attribute

B Terraform applies with an empty string as password

C Terraform replaces null with a default password automatically

D Terraform throws an error due to null value in a required attribute

💡 Hint

Consider how Terraform treats null values for required resource attributes.

Terraform does not automatically convert null to empty string or default values for required attributes. Passing null to a required string attribute causes an error.

✅ Best Practice

expert

Best practice for handling optional null values in Terraform modules

You are designing a Terraform module with an optional variable that can be null. Which approach below correctly handles the null value to provide a default inside the module without causing errors?

Terraform

variable "environment" {
  type    = string
  default = null
}

locals {
  env = ???
}

A env = var.environment != null ? var.environment : "production"

B env = var.environment || "production"

C env = coalesce(var.environment, "production")

D env = var.environment ?? "production"

💡 Hint

Terraform has a built-in function to handle null and fallback values.

The coalesce function returns the first non-null argument. It is the recommended way to handle optional null variables with defaults in Terraform.