Null values handling in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign a default value if the variable is null.

Terraform

variable "instance_type" {
  type    = string
  default = [1]
}

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

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

A"t2.micro"

B"m5.large"

Cnull

D""

Attempts:

3 left

💡 Hint

Common Mistakes

Setting default to an empty string instead of null

Not handling null in the resource block

The variable default is set to null to allow overriding. The resource uses a conditional to assign t2.micro if the variable is null.

2fill in blank

medium

Complete the code to use the coalesce function to handle null values.

Terraform

resource "aws_s3_bucket" "example" {
  bucket = coalesce(var.bucket_name, [1])
  acl    = "private"
}

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

A"default-bucket"

Bnull

C""

D"public-bucket"

Attempts:

3 left

💡 Hint

Common Mistakes

Using null as fallback which causes errors

Using empty string which is invalid bucket name

The coalesce function returns the first non-null argument. If var.bucket_name is null, it uses "default-bucket".

3fill in blank

hard

Fix the error in the code to correctly handle null values in a list variable.

Terraform

variable "subnets" {
  type    = list(string)
  default = [1]
}

resource "aws_instance" "example" {
  count         = length(var.subnets)
  subnet_id     = var.subnets[count.index]
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

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

A[]

B[""]

C[null]

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting default to null instead of empty list

Using list with null element which causes index errors

The default should be an empty list [] so length(var.subnets) returns 0 and count = 0, preventing index access errors. Null causes plan-time errors on length(null).

4fill in blank

hard

Fill both blanks to create a map that excludes null values using the compact function.

Terraform

locals {
  raw_tags = {
    Name        = var.name
    Environment = var.environment
    Owner       = [1]
  }

  filtered_tags = zipmap(keys([2]), compact(values([2])))
}

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

Avar.owner

Blocal.raw_tags

Cvar.tags

Dvar.owner != null ? var.owner : "unknown"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the wrong variable to compact

Using a conditional expression inside the map instead of compact

The raw_tags map includes var.owner which may be null. values(local.raw_tags) produces a list, compact removes nulls, and zipmap(keys(local.raw_tags), ...) reconstructs the map without null-value entries.

5fill in blank

hard

Fill all three blanks to safely access nested attributes that may be null using the lookup function.

Terraform

resource "aws_instance" "example" {
  ami           = lookup(var.ami_map, [1], [2])
  instance_type = lookup(var.instance_types, [3], "t2.micro")
}

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

A"us-east-1"

B"ami-123456"

C"us-west-2"

D"m5.large"

Attempts:

3 left

💡 Hint

Common Mistakes

Using values instead of keys in lookup

Not providing a default value causing errors

The lookup function safely retrieves values from maps. It uses a key and a default if the key is missing or null. Here, "us-east-1" and "us-west-2" are keys, and "ami-123456" is the default AMI.