Immutable infrastructure concept in Terraform - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a new AWS EC2 instance resource.

Terraform

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "[1]"
}

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

Am5.large

Bt3.micro

Ct2.micro

Dc5.xlarge

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance types that are too large for simple examples.

Typo in instance type string.

The instance_type must be a valid AWS instance type. Here, t3.micro is a common choice for small instances.

2fill in blank

medium

Complete the code to add a tag to the AWS instance for identification.

Terraform

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t3.micro"

  tags = {
    Name = "[1]"
  }
}

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

AMyServer

BOldServer

CTemporary

DProduction

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving the tag value empty.

Using names that are not descriptive.

Tags help identify resources. Here, MyServer is a friendly name for the instance.

3fill in blank

hard

Fix the error in the code to ensure immutable infrastructure by replacing the instance on change.

Terraform

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t3.micro"

  lifecycle {
    [1] = true
  }
}

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

Aprevent_destroy

Breplace_triggered_by

Cignore_changes

Dcreate_before_destroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using prevent_destroy which blocks deletion.

Ignoring changes instead of replacing.

The create_before_destroy lifecycle rule tells Terraform to create the new instance before destroying the old one, supporting immutable infrastructure.

4fill in blank

hard

Fill both blanks to create a new versioned AMI and use it in the instance resource.

Terraform

resource "aws_ami" "example_ami" {
  name                = "example-ami-[1]"
  virtualization_type = "hvm"
  root_device_name    = "/dev/sda1"
  ebs_block_device {
    device_name = "/dev/sda1"
    volume_size = 8
  }
}

resource "aws_instance" "example" {
  ami           = aws_ami.example_ami.[2]
  instance_type = "t3.micro"
}

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

Av1

Bid

Carn

Dlatest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'latest' which is not an attribute of aws_ami resource.

Using 'arn' instead of 'id' for AMI reference.

The AMI name includes a version like v1 to track changes. The instance uses the AMI's id to launch.

5fill in blank

hard

Fill all three blanks to define a Terraform output that shows the public IP of the new instance.

Terraform

output "instance_public_ip" {
  value = aws_instance.example.[1]
  description = "[2] of the instance"
  sensitive = [3]
}

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

Apublic_ip

BPublic IP address

Cfalse

Dprivate_ip

Attempts:

3 left

💡 Hint

Common Mistakes

Using private_ip instead of public_ip.

Marking output as sensitive when it is not.

The output shows the public_ip attribute. The description explains it is the Public IP address. The output is not sensitive, so false is used.

Practice

1. What does the term immutable infrastructure mean in Terraform?

easy

A. Replacing resources instead of modifying them in place

B. Changing resources directly without replacement

C. Manually updating resources outside Terraform

D. Using mutable variables to configure resources

Solution

1. Step 1: Understand the definition of immutable infrastructure

   Immutable infrastructure means you do not change existing resources but replace them entirely when updates are needed.

2. Step 2: Compare options with this definition

   Only Replacing resources instead of modifying them in place describes replacing resources instead of modifying them, which matches the concept.

3. Final Answer:

   Replacing resources instead of modifying them in place -> Option A

4. Quick Check:

   Immutable infrastructure = Replace, not modify [OK]

Hint: Immutable means replace, not change existing resources [OK]

Common Mistakes:

• Thinking mutable means immutable
• Confusing manual updates with Terraform-managed changes
• Assuming resources are changed in place

2. Which Terraform lifecycle argument helps implement immutable infrastructure by creating new resources before destroying old ones?

easy

A. ignore_changes

B. prevent_destroy

C. create_before_destroy

D. replace_triggered_by

Solution

1. Step 1: Identify lifecycle arguments related to resource replacement

   Terraform lifecycle has arguments like create_before_destroy, prevent_destroy, ignore_changes, and replace_triggered_by.

2. Step 2: Match argument to immutable infrastructure behavior

   Create_before_destroy ensures new resource is created before old one is destroyed, supporting immutable infrastructure.

3. Final Answer:

   create_before_destroy -> Option C

4. Quick Check:

   Lifecycle create_before_destroy = create new before delete old [OK]

Hint: Use create_before_destroy to replace safely [OK]

Common Mistakes:

• Confusing prevent_destroy with create_before_destroy
• Using ignore_changes which skips updates but doesn't replace
• Misunderstanding replace_triggered_by purpose

3. Given this Terraform resource snippet with lifecycle:

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

  lifecycle {
    create_before_destroy = true
  }
}

What happens when you change instance_type from t2.micro to t2.small?

medium

A. Terraform creates a new instance first, then destroys the old one

B. Terraform ignores the change due to lifecycle rules

C. Terraform destroys the old instance first, then creates a new one

D. Terraform updates the existing instance in place

Solution

1. Step 1: Understand create_before_destroy lifecycle effect

   This setting tells Terraform to create the new resource before destroying the old one to avoid downtime.

2. Step 2: Apply this to instance_type change

   Changing instance_type requires replacement, so Terraform creates new instance first, then destroys old.

3. Final Answer:

   Terraform creates a new instance first, then destroys the old one -> Option A

4. Quick Check:

   create_before_destroy means create new before destroy old [OK]

Hint: create_before_destroy means new resource first [OK]

Common Mistakes:

• Assuming in-place update happens
• Thinking old resource is destroyed before new is ready
• Believing lifecycle ignores changes

4. You wrote this Terraform lifecycle block:

lifecycle {
  create_before_destroy = false
}

But you want to implement immutable infrastructure with zero downtime. What is the problem?

medium

A. Terraform will create duplicate resources without destroying old ones

B. Terraform will not replace resources at all

C. Terraform will ignore lifecycle block and update in place

D. Resources will be destroyed before new ones are created, causing downtime

Solution

1. Step 1: Analyze create_before_destroy false effect

   When false, Terraform destroys old resource before creating new one, causing downtime.

2. Step 2: Match with immutable infrastructure goal

   Immutable infrastructure aims for zero downtime by creating new resource first, so false breaks this goal.

3. Final Answer:

   Resources will be destroyed before new ones are created, causing downtime -> Option D

4. Quick Check:

   False create_before_destroy = destroy first, downtime risk [OK]

Hint: False create_before_destroy causes downtime risk [OK]

Common Mistakes:

• Thinking false means no replacement
• Assuming lifecycle block is ignored
• Believing duplicates are created without destroy

5. You want to deploy a web server with immutable infrastructure using Terraform. Which combination of lifecycle settings and resource management best supports this goal?

hard

A. Use ignore_changes on all attributes to prevent updates

B. Use create_before_destroy = true and avoid manual changes outside Terraform

C. Use prevent_destroy = true to stop any resource replacement

D. Manually update resources and disable Terraform lifecycle rules

Solution

1. Step 1: Identify lifecycle settings that enable immutable infrastructure

   Create_before_destroy = true ensures new resource is ready before old is removed, supporting immutable infrastructure.

2. Step 2: Consider resource management best practices

   Avoid manual changes outside Terraform to keep infrastructure consistent and manageable.

3. Final Answer:

   Use create_before_destroy = true and avoid manual changes outside Terraform -> Option B

4. Quick Check:

   Immutable infrastructure = create_before_destroy + Terraform-only changes [OK]

Hint: Combine create_before_destroy with Terraform-only changes [OK]

Common Mistakes:

• Using prevent_destroy which blocks replacement
• Ignoring changes disables updates, not replacement
• Manual changes cause drift and errors