Immutable infrastructure concept in Terraform - Mini Project: Build & Apply

Immutable Infrastructure Concept with Terraform

📖 Scenario: You are working as a cloud engineer. Your team wants to use immutable infrastructure to deploy a simple web server. This means instead of changing the existing server, you will create a new server each time you deploy. This helps avoid errors and keeps the system stable.

🎯 Goal: Build a Terraform configuration that creates an AWS EC2 instance with immutable infrastructure principles. You will first define the instance data, then add a configuration variable, apply the main resource block, and finally complete the setup with a tag to identify the instance.

📋 What You'll Learn

Use Terraform to define AWS EC2 instance configuration

Create a variable for the AMI ID

Define the EC2 instance resource using the variable

Add a tag to the instance for identification

💡 Why This Matters

🌍 Real World

Immutable infrastructure helps teams deploy cloud servers safely by replacing servers instead of changing them. This reduces errors and downtime.

💼 Career

Cloud engineers and DevOps professionals use Terraform and immutable infrastructure to automate and improve cloud deployments.

1

Define the AWS provider and instance data

Write Terraform code to set the AWS provider with region us-east-1 and create a variable called ami_id with default value "ami-0c55b159cbfafe1f0".

Terraform

# Set AWS provider and define ami_id variable
# Your code here

Hint

Use provider "aws" block to set the region. Use variable "ami_id" block with default to set the AMI ID.

2

Add instance type configuration

Add a variable called instance_type with default value "t2.micro" to specify the EC2 instance type.

Terraform

provider "aws" {
  region = "us-east-1"
}

variable "ami_id" {
  default = "ami-0c55b159cbfafe1f0"
}

# Define instance_type variable
# Your code here

Hint

Use a variable block named instance_type with a default value.

3

Create the EC2 instance resource

Write a resource block named aws_instance with name web_server. Use var.ami_id for the AMI and var.instance_type for the instance type.

Terraform

provider "aws" {
  region = "us-east-1"
}

variable "ami_id" {
  default = "ami-0c55b159cbfafe1f0"
}

variable "instance_type" {
  default = "t2.micro"
}

# Create aws_instance resource named web_server
# Your code here

Hint

Use resource "aws_instance" "web_server" block. Set ami and instance_type using variables.

4

Add a Name tag to the EC2 instance

Inside the aws_instance.web_server resource, add a tags block with Name = "ImmutableWebServer" to identify the instance.

Terraform

provider "aws" {
  region = "us-east-1"
}

variable "ami_id" {
  default = "ami-0c55b159cbfafe1f0"
}

variable "instance_type" {
  default = "t2.micro"
}

resource "aws_instance" "web_server" {
  ami           = var.ami_id
  instance_type = var.instance_type

  # Add tags block here
  # Your code here
}

Hint

Inside the resource block, add tags = { Name = "ImmutableWebServer" } to label the instance.

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