Outputs for module communication in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What is the output value of the root module after applying this Terraform configuration?

Given a root module that calls a child module which outputs a value, what will be the value of module.child.output_value in the root module?

Terraform

module "child" {
  source = "./child_module"
  input_var = "hello"
}

output "child_output" {
  value = module.child.output_value
}

# child_module/main.tf
variable "input_var" {}

output "output_value" {
  value = "${var.input_var}-world"
}

A "hello-world"

B "hello"

C "world"

D "${var.input_var}-world"

💡 Hint

Remember that module outputs can be accessed in the root module using module...

The child module outputs the value by appending '-world' to the input variable 'hello'. The root module accesses this output via module.child.output_value, so the final output is 'hello-world'.

❓ Configuration

intermediate

Which option correctly defines an output in a Terraform module to expose a resource attribute?

You want to expose the ID of an AWS EC2 instance created inside a module. Which output block correctly achieves this?

Terraform

resource "aws_instance" "example" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

# Define output here

A

output "instance_id" {
  value = aws_instance.example.id
}

B

output "instance_id" {
  value = aws_instance.example[0].id
}

C

output "instance_id" {
  value = aws_instance.example.instance_id
}

D

output "instance_id" {
  value = aws_instance.example
}

💡 Hint

Resource attributes are accessed by their exact attribute names, not by index or the whole resource.

The correct attribute for the instance ID is 'id'. Option A correctly references it. Option A uses a non-existent attribute 'instance_id'. Option A tries to index a non-list resource. Option A returns the whole resource, which is invalid for output value.

❓ Architecture

advanced

How can you pass a computed value from one module to another in Terraform?

You have two modules: Module A creates a VPC and outputs its ID. Module B needs the VPC ID to create subnets. How should you connect these modules in the root module?

Terraform

module "vpc" {
  source = "./vpc_module"
}

module "subnet" {
  source = "./subnet_module"
  vpc_id = ???
}

A Set vpc_id = output.vpc_id

B Set vpc_id = var.vpc_id

C Set vpc_id = aws_vpc.main.id

D Set vpc_id = module.vpc.vpc_id_output

💡 Hint

Modules expose outputs that can be referenced by other modules in the root module.

Module outputs are accessed using module... So to pass the VPC ID from Module A to Module B, you assign vpc_id = module.vpc.vpc_id_output in the root module.

❓ security

advanced

What is a security risk when exposing sensitive data via Terraform module outputs?

You have a module output that exposes a database password. What is the main risk and how can you mitigate it?

A The password is stored in plain text in logs; mitigate by disabling logging.

B The password is encrypted in state files; no mitigation needed.

C The password appears in Terraform state files; mitigate by marking the output as sensitive.

D The password is only visible to admins; mitigate by restricting IAM roles.

💡 Hint

Terraform state files store outputs and can be read if not protected.

Terraform state files store output values in plain text by default. Marking outputs as sensitive hides them from CLI output and reduces accidental exposure. This is the recommended mitigation.

✅ Best Practice

expert

What is the best practice for managing outputs when a module is used multiple times with different configurations?

You use the same module twice to create two different environments (dev and prod). How should you handle outputs to avoid conflicts and confusion?

A Avoid using outputs; instead, hardcode values in the root module.

B Use unique module instance names and reference outputs with those names in the root module.

C Define outputs only in one module instance and share them via variables.

D Use the same module name and rely on Terraform to merge outputs automatically.

💡 Hint

Terraform distinguishes module instances by their names in the root module.

Each module instance should have a unique name in the root module. Outputs are accessed via these names, preventing conflicts and making it clear which environment's output is referenced.