Terraform's declarative approach - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean that Terraform uses a declarative approach?

Terraform lets you declare the desired state of your infrastructure, and it figures out how to reach that state automatically.

beginner

How does Terraform know what changes to make when you update your configuration?

Terraform compares the current state of your infrastructure with the desired state you declared, then plans and applies only the necessary changes.

beginner

Why is Terraform's declarative approach helpful compared to manual setup?

It reduces mistakes by automating changes, ensures consistency, and makes it easy to track and repeat setups.

intermediate

In Terraform, what file stores the current state of your infrastructure?

The terraform.tfstate file stores the current state, helping Terraform know what exists and what needs updating.

beginner

What command in Terraform shows you the changes it will make before applying them?

The terraform plan command previews the changes Terraform will make to reach the desired state.

What is the main idea behind Terraform's declarative approach?

A Terraform randomly changes resources

B You write step-by-step instructions for changes

C You manually update resources one by one

D You declare the desired end state and Terraform figures out the steps

Terraform uses a declarative approach where you declare the desired state, and it plans the steps to reach it.

Which file does Terraform use to track the current infrastructure state?

A main.tf

B variables.tf

C terraform.tfstate

D outputs.tf

The terraform.tfstate file stores the current state of your infrastructure.

What does the terraform plan command do?

A Deletes all resources

B Shows the changes Terraform will make

C Applies changes immediately

D Creates a backup of your code

terraform plan previews the changes before applying them.

Why is using a declarative tool like Terraform better than manual setup?

A It automates changes and reduces errors

B It only works for small projects

C It requires no learning

D It makes changes randomly

Terraform automates infrastructure changes, reducing mistakes and ensuring consistency.

When you update your Terraform configuration, what happens next?

A Terraform compares current and desired states and updates only what changed

B Terraform ignores the changes

C Terraform deletes everything and starts over

D Terraform asks you to manually update resources

Terraform compares the current state with the desired state and applies only necessary updates.

Explain in your own words how Terraform's declarative approach works and why it is useful.

Think about how you tell Terraform what you want, not how to do it.

Describe the role of the terraform.tfstate file in Terraform's workflow.

It's like Terraform's memory of what exists.

Practice

1. What does Terraform's declarative approach mean?
terraform apply will create resources based on what you specify, not how to create them.

easy

A. You describe the desired state of infrastructure, not the steps to create it.

B. You write scripts that run commands step-by-step to build infrastructure.

C. You manually create resources in the cloud console and Terraform tracks them.

D. You use Terraform only to delete resources, not create them.

Solution

1. Step 1: Understand declarative vs imperative

   Declarative means describing the end state, while imperative means describing the steps to get there.

2. Step 2: Apply to Terraform

   Terraform uses declarative approach by letting you write configuration files that describe what you want, not how to do it.

3. Final Answer:

   You describe the desired state of infrastructure, not the steps to create it. -> Option A

4. Quick Check:

   Declarative = Describe desired state [OK]

Hint: Declarative means say what, not how [OK]

Common Mistakes:

• Confusing declarative with imperative scripting
• Thinking Terraform runs commands step-by-step
• Believing Terraform only deletes resources

2. Which Terraform configuration snippet correctly declares an AWS S3 bucket named "mybucket"?

easy

A. resource aws_s3_bucket mybucket { bucket_name = "mybucket" }

B. create aws_s3_bucket mybucket { name = "mybucket" }

C. aws_s3_bucket "mybucket" { bucket_name = "mybucket" }

D. resource "aws_s3_bucket" "mybucket" { bucket = "mybucket" }

Solution

1. Step 1: Identify correct Terraform resource syntax

   Terraform resource blocks start with 'resource', then resource type in quotes, then resource name in quotes, followed by braces with arguments.

2. Step 2: Match correct attribute names

   The attribute to name an S3 bucket is 'bucket', not 'bucket_name'. resource "aws_s3_bucket" "mybucket" { bucket = "mybucket" } matches correct syntax and attribute.

3. Final Answer:

   resource "aws_s3_bucket" "mybucket" { bucket = "mybucket" } -> Option D

4. Quick Check:

   Correct resource block syntax = resource "aws_s3_bucket" "mybucket" { bucket = "mybucket" } [OK]

Hint: Terraform resource blocks start with resource "type" "name" [OK]

Common Mistakes:

• Using incorrect keywords like 'create' instead of 'resource'
• Missing quotes around resource type or name
• Using wrong attribute names like 'bucket_name'

3. Given this Terraform configuration:

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

What will Terraform do when you run terraform apply for the first time?

medium

A. It will delete any existing EC2 instances named example.

B. It will only plan the changes but not create any resources.

C. It will create an AWS EC2 instance with the specified AMI and instance type.

D. It will throw a syntax error due to missing provider block.

Solution

1. Step 1: Understand resource declaration effect

   The resource block declares an EC2 instance with given AMI and type. Terraform will create it on apply.

2. Step 2: Consider first apply behavior

   On first apply, Terraform creates resources to match the declared state. Missing provider block is not a syntax error but requires provider configuration elsewhere.

3. Final Answer:

   It will create an AWS EC2 instance with the specified AMI and instance type. -> Option C

4. Quick Check:

   First apply creates declared resources [OK]

Hint: terraform apply creates resources declared first time [OK]

Common Mistakes:

• Confusing plan with apply behavior
• Expecting deletion instead of creation
• Assuming missing provider block causes syntax error

4. You wrote this Terraform code:

resource "aws_s3_bucket" "bucket" {
  bucket = "mybucket"
  acl    = "public-read"
}

But Terraform apply fails with an error about bucket name already existing. What is the best fix?

medium

A. Change the bucket name to a unique one because S3 bucket names must be globally unique.

B. Remove the acl attribute to fix the error.

C. Rename the resource block from "bucket" to "mybucket".

D. Run terraform destroy before apply to clear existing buckets.

Solution

1. Step 1: Understand S3 bucket naming rules

   S3 bucket names must be globally unique across all AWS accounts.

2. Step 2: Analyze error cause

   The error means the bucket name "mybucket" is already taken by someone else, so Terraform cannot create it.

3. Step 3: Choose fix

   Changing the bucket name to a unique one solves the problem. Other options do not address uniqueness.

4. Final Answer:

   Change the bucket name to a unique one because S3 bucket names must be globally unique. -> Option A

5. Quick Check:

   S3 bucket names must be unique globally [OK]

Hint: S3 bucket names must be unique globally [OK]

Common Mistakes:

• Thinking acl attribute causes name conflict
• Renaming resource block does not change bucket name
• Destroying resources unnecessarily

5. You want to manage a set of AWS EC2 instances with Terraform declaratively. You have a list of instance names and want to create one instance per name. Which Terraform feature best fits this declarative approach?

hard

A. Manually create each instance resource block with a unique name.

B. Use a for_each meta-argument on the resource block with the list of names.

C. Write a shell script to loop and run terraform apply multiple times.

D. Use a count meta-argument with a fixed number and hardcoded names.

Solution

1. Step 1: Understand declarative resource creation for multiple items

   Terraform's for_each lets you declare multiple instances based on a collection, matching the declarative style.

2. Step 2: Evaluate options

   Shell scripts and manual blocks are imperative or repetitive, not declarative. Using count with hardcoded names is less flexible than for_each.

3. Final Answer:

   Use a for_each meta-argument on the resource block with the list of names. -> Option B

4. Quick Check:

   for_each creates resources declaratively from collections [OK]

Hint: for_each creates multiple resources declaratively [OK]

Common Mistakes:

• Using imperative loops outside Terraform
• Hardcoding multiple resource blocks manually
• Using count without dynamic naming