Declarative vs imperative IaC in Terraform - Quick Revision & Key Differences

Recall & Review

beginner

What does declarative IaC mean?

Declarative IaC means you describe the desired final state of your infrastructure, and the tool figures out how to get there.

beginner

What is imperative IaC?

Imperative IaC means you write step-by-step instructions telling the system exactly how to create or change resources.

beginner

Give an example of a declarative IaC tool.

Terraform is an example of a declarative IaC tool. You write what you want, not how to do it.

beginner

Why is declarative IaC often easier for beginners?

Because you only focus on the end result, not the detailed steps. The tool handles the complexity.

intermediate

What is a key challenge of imperative IaC?

You must manage the exact order of steps, which can be complex and error-prone.

Which IaC style focuses on describing the desired end state?

A Declarative

B Imperative

C Procedural

D Manual

Declarative IaC describes the final state you want, letting the tool handle the steps.

Terraform is an example of which IaC style?

A Imperative

B Declarative

C Manual

D Scripting

Terraform uses declarative syntax to define infrastructure.

Which IaC style requires you to write step-by-step instructions?

A Imperative

B Automatic

C Descriptive

D Declarative

Imperative IaC means you specify the exact steps to create or change resources.

What is a benefit of declarative IaC?

A It requires detailed scripting knowledge

B You control every step manually

C It reduces complexity by focusing on the end state

D It cannot be automated

Declarative IaC reduces complexity by letting the tool manage the steps.

Which IaC style can be more error-prone due to step ordering?

A Declarative

B Automatic

C None

D Imperative

Imperative IaC requires careful step ordering, which can cause errors.

Explain the difference between declarative and imperative IaC in simple terms.

Think about telling a friend what you want versus telling them exactly how to do it.

Why might someone choose declarative IaC like Terraform over imperative IaC?

Consider the benefits of focusing on the goal instead of the process.

Practice

1. What is the main difference between declarative and imperative Infrastructure as Code (IaC)?

easy

A. Declarative IaC describes the desired end state, while imperative IaC specifies exact steps to reach it.

B. Declarative IaC requires manual commands, while imperative IaC is fully automatic.

C. Declarative IaC is only for cloud, imperative IaC is for on-premises.

D. Declarative IaC uses scripts, imperative IaC uses configuration files.

Solution

1. Step 1: Understand declarative IaC

   Declarative IaC focuses on describing the final desired state of infrastructure without specifying how to achieve it.

2. Step 2: Understand imperative IaC

   Imperative IaC lists the exact commands or steps needed to create or change infrastructure.

3. Final Answer:

   Declarative IaC describes the desired end state, while imperative IaC specifies exact steps to reach it. -> Option A

4. Quick Check:

   Declarative = final state, Imperative = steps [OK]

Hint: Declarative = what you want; imperative = how to do it [OK]

Common Mistakes:

• Confusing declarative with imperative steps
• Thinking declarative requires manual commands
• Assuming declarative only works for cloud

2. Which of the following Terraform code snippets correctly shows a declarative resource definition?

easy

A. create_instance("ami-123", "t2.micro")

B. resource "aws_instance" "web" { ami = "ami-123" instance_type = "t2.micro" }

C. if not instance_exists() then create_instance()

D. run_command("aws ec2 run-instances --image-id ami-123")

Solution

1. Step 1: Identify declarative syntax

   Terraform resource blocks declare the desired state, like the resource "aws_instance" "web" { ... } block.

2. Step 2: Compare with imperative styles

   Options B, C, and D show commands or logic steps, which are imperative, not declarative.

3. Final Answer:

   The Terraform resource block syntax is declarative. -> Option B

4. Quick Check:

   Terraform resource block = declarative [OK]

Hint: Terraform resource blocks are declarative descriptions [OK]

Common Mistakes:

• Choosing imperative command syntax as declarative
• Confusing function calls with resource declarations
• Ignoring the resource block structure

3. Given this Terraform snippet, what will Terraform do when you run terraform apply if the AWS instance does not exist yet?

resource "aws_instance" "example" {
  ami           = "ami-abc123"
  instance_type = "t2.micro"
}

medium

A. Terraform will prompt for manual commands to create the instance.

B. Terraform will delete any existing instances and do nothing else.

C. Terraform will create a new AWS instance with the specified AMI and instance type.

D. Terraform will throw a syntax error because the resource block is incomplete.

Solution

1. Step 1: Understand Terraform apply behavior

   Terraform compares the current state with the desired state defined in the resource block.

2. Step 2: Predict action if resource missing

   If the AWS instance does not exist, Terraform will create it to match the declared state.

3. Final Answer:

   Terraform will create a new AWS instance with the specified AMI and instance type. -> Option C

4. Quick Check:

   Missing resource = Terraform creates it [OK]

Hint: Terraform creates missing resources to match declared state [OK]

Common Mistakes:

• Thinking Terraform deletes resources by default
• Expecting manual commands during apply
• Assuming syntax error in valid resource block

4. You wrote this Terraform code but terraform apply fails with an error:

resource "aws_instance" "web" {
  ami = "ami-123"
  instance_type = t2.micro
}

What is the likely cause of the error?

medium

A. Terraform requires an explicit create command inside the resource block.

B. The resource name "web" is invalid and must be changed.

C. The AMI ID "ami-123" is not allowed in Terraform.

D. Missing quotes around the instance_type value causes a syntax error.

Solution

1. Step 1: Check syntax of resource attributes

   Terraform requires string values to be in quotes. The instance_type value is missing quotes.

2. Step 2: Identify error cause

   Missing quotes cause a syntax error, preventing Terraform from parsing the file.

3. Final Answer:

   Missing quotes around the instance_type value causes a syntax error. -> Option D

4. Quick Check:

   Strings need quotes in Terraform [OK]

Hint: Always quote string values in Terraform resource blocks [OK]

Common Mistakes:

• Ignoring missing quotes around strings
• Thinking resource names cause syntax errors
• Expecting commands inside resource blocks

5. You want to create a cloud infrastructure using Terraform declarative IaC. Which approach best fits this goal?

hard

A. Write a Terraform configuration file describing the desired resources and run terraform apply.

B. Write a script with commands to create each resource step-by-step manually.

C. Manually create resources in the cloud console, then import them into Terraform.

D. Use a shell script to run cloud CLI commands in order.

Solution

1. Step 1: Understand declarative IaC goal

   Declarative IaC means describing the final infrastructure state in configuration files.

2. Step 2: Identify Terraform usage

   Terraform uses configuration files to declare resources, then applies changes automatically.

3. Final Answer:

   Write a Terraform configuration file describing the desired resources and run terraform apply. -> Option A

4. Quick Check:

   Declarative IaC = config files + apply [OK]

Hint: Use Terraform config files, not manual scripts, for declarative IaC [OK]

Common Mistakes:

• Confusing declarative IaC with manual scripting
• Thinking manual cloud console use is declarative
• Using imperative CLI commands instead of config files