Immutable infrastructure concept in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Immutable Infrastructure Benefits

Which of the following is the primary benefit of using immutable infrastructure?

A It reduces configuration drift by replacing servers instead of changing them.

B It allows quick updates by modifying existing servers directly.

C It requires manual intervention for every update to ensure accuracy.

D It increases downtime because servers are updated in place.

💡 Hint

Think about how replacing servers instead of changing them affects consistency.

Immutable infrastructure means servers are replaced rather than changed, which reduces errors and configuration drift.

❓ Architecture

intermediate

Immutable Infrastructure Deployment Pattern

In an immutable infrastructure deployment, what is the recommended approach to update an application running on cloud servers?

A Deploy a new server image with the updated application and replace old servers.

B SSH into each server and update the application manually.

C Patch the running servers with update scripts during maintenance windows.

D Use configuration management tools to change application files on live servers.

💡 Hint

Consider how immutable infrastructure treats servers as replaceable units.

Immutable infrastructure updates by deploying new server images and replacing old ones, avoiding manual or live changes.

❓ Configuration

advanced

Terraform Immutable Infrastructure Example

Given the following Terraform snippet, what will happen when you change the AMI ID and apply the configuration?

resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"
  tags = {
    Name = "web-server"
  }
}

Terraform

resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"
  tags = {
    Name = "web-server"
  }
}

A Terraform will update the existing instance in place with the new AMI.

B Terraform will destroy the old instance and create a new one with the new AMI.

C Terraform will ignore the AMI change and keep the old instance.

D Terraform will throw a syntax error due to missing lifecycle block.

💡 Hint

Think about how Terraform handles changes to immutable properties like AMI.

Changing the AMI causes Terraform to replace the instance because AMI is immutable for an existing instance.

❓ security

advanced

Security Advantages of Immutable Infrastructure

Which security advantage is most directly improved by adopting immutable infrastructure?

A Increased complexity in managing firewall rules.

B Easier manual auditing of server configurations.

C Ability to patch live servers quickly without downtime.

D Reduced risk of unauthorized changes persisting on servers.

💡 Hint

Consider how replacing servers affects unauthorized changes.

Immutable infrastructure reduces risk of unauthorized changes because servers are replaced rather than modified.

❓ service_behavior

expert

Behavior of Load Balancer During Immutable Deployment

During an immutable infrastructure deployment, how should a load balancer be configured to minimize downtime when replacing backend servers?

A Keep old and new servers in the load balancer simultaneously without health checks.

B Remove old servers immediately before creating new servers to avoid conflicts.

C Remove old servers from the load balancer only after new servers pass health checks.

D Manually switch traffic to new servers after all old servers are terminated.

💡 Hint

Think about how to keep service available during server replacement.

Removing old servers only after new ones are healthy ensures continuous service without downtime.

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