Data source vs resource difference in Terraform - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Terraform Data Sources

In Terraform, what is the primary purpose of a data source?

A To delete existing infrastructure resources

B To create new infrastructure resources managed by Terraform

C To fetch and use information about existing infrastructure outside Terraform's control

D To define variables for Terraform configurations

💡 Hint

Think about whether data sources create or just read information.

Data sources in Terraform are used to read or fetch information about existing infrastructure that Terraform does not manage directly. They do not create or modify resources.

🧠 Conceptual

intermediate

Terraform Resource Behavior

Which statement best describes a resource in Terraform?

A It is a temporary placeholder with no real effect

B It only reads information from existing infrastructure

C It is used to store configuration variables

D It represents infrastructure components that Terraform creates and manages

💡 Hint

Resources are the main building blocks Terraform controls.

Resources in Terraform define infrastructure components that Terraform creates, updates, and deletes as part of managing your infrastructure.

❓ Architecture

advanced

Choosing Between Data Source and Resource

You want to use an existing AWS VPC ID in your Terraform configuration without creating a new VPC. Which is the best approach?

A Use a <code>resource</code> block to create a new VPC with the existing ID

B Use a <code>data</code> block to fetch the existing VPC ID

C Use a variable to hardcode the VPC ID without fetching it

D Use a <code>resource</code> block to import the existing VPC

💡 Hint

Think about how to reference existing infrastructure without creating it.

Using a data source allows Terraform to read the existing VPC ID without managing or creating it. Creating a resource would attempt to create a new VPC.

❓ service_behavior

advanced

Terraform Resource Lifecycle Behavior

What happens when you remove a resource block from your Terraform configuration and run terraform apply?

A Terraform deletes the corresponding infrastructure resource

B Terraform ignores the resource and leaves it unchanged

C Terraform converts the resource into a data source

D Terraform throws an error and stops

💡 Hint

Consider how Terraform manages resources it no longer sees in the config.

When a resource block is removed, Terraform plans to delete the actual infrastructure resource to match the configuration state.

❓ security

expert

Security Implications of Using Data Sources

Which security risk is most relevant when using Terraform data sources to fetch sensitive information like passwords or keys?

A Sensitive data may be exposed in Terraform state files if not encrypted

B Data sources automatically encrypt sensitive data in logs

C Using data sources disables Terraform's access controls

D Data sources prevent any sensitive data from being stored locally

💡 Hint

Think about where Terraform stores fetched data and how it handles sensitive info.

Terraform stores all fetched data, including sensitive info from data sources, in its state file. If the state file is not secured or encrypted, this can expose secrets.

Practice

1. What is the main difference between a resource and a data source in Terraform?

easy

A. Resources and data sources both create infrastructure but in different clouds.

B. Resources create or manage infrastructure; data sources only read existing information.

C. Resources only read existing infrastructure; data sources create new infrastructure.

D. Resources are temporary; data sources are permanent.

Solution

1. Step 1: Understand resource role

   Resources in Terraform are used to create or manage cloud infrastructure components.

2. Step 2: Understand data source role

   Data sources are used to read information about existing infrastructure without changing it.

3. Final Answer:

   Resources create or manage infrastructure; data sources only read existing information. -> Option B

4. Quick Check:

   Resource = create/manage, Data source = read [OK]

Hint: Resources build; data sources just look up info [OK]

Common Mistakes:

• Thinking data sources create resources
• Confusing resource and data source roles
• Assuming both modify infrastructure
• Believing data sources are temporary

2. Which of the following is the correct syntax to declare a data source in Terraform?

easy

A. data "aws_ami" "example" {}

B. resource "aws_instance" "example" {}

C. source "aws_vpc" "example" {}

D. resource "data_aws_subnet" "example" {}

Solution

1. Step 1: Identify data source syntax

   Data sources use the keyword data followed by the type and name.

2. Step 2: Check options

   data "aws_ami" "example" {} uses data "aws_ami" "example" {}, which is correct syntax for a data source.

3. Final Answer:

   data "aws_ami" "example" {} -> Option A

4. Quick Check:

   Data source starts with 'data' keyword [OK]

Hint: Data sources start with 'data' keyword [OK]

Common Mistakes:

• Using 'resource' keyword for data sources
• Mixing 'source' keyword which doesn't exist
• Prefixing resource with 'data_' incorrectly
• Confusing resource and data source syntax

3. Given this Terraform snippet:

data "aws_vpc" "selected" {
  filter {
    name   = "tag:Name"
    values = ["main-vpc"]
  }
}

resource "aws_subnet" "example" {
  vpc_id     = data.aws_vpc.selected.id
  cidr_block = "10.0.1.0/24"
}

What does the data.aws_vpc.selected.id represent?

medium

A. The ID of an existing VPC filtered by tag "Name=main-vpc".

B. The ID of a subnet created inside the VPC.

C. A random VPC ID generated by Terraform.

D. The ID of a new VPC created by Terraform.

Solution

1. Step 1: Analyze data source usage

   The data "aws_vpc" "selected" block reads an existing VPC filtered by the tag "Name=main-vpc".

2. Step 2: Understand reference in resource

   The resource aws_subnet.example uses data.aws_vpc.selected.id to get the ID of that existing VPC to create a subnet inside it.

3. Final Answer:

   The ID of an existing VPC filtered by tag "Name=main-vpc". -> Option A

4. Quick Check:

   Data source reads existing VPC ID [OK]

Hint: Data source reads existing resource info [OK]

Common Mistakes:

• Thinking data source creates new VPC
• Confusing subnet ID with VPC ID
• Assuming random ID generation
• Using resource instead of data source for existing info

4. You wrote this Terraform code but get an error:

resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

data "aws_vpc" "main" {
  id = aws_vpc.main.id
}

What is the problem?

medium

A. The data source block is missing a filter instead of id.

B. Data sources cannot reference resources in the same configuration.

C. You cannot use the same name for resource and data source.

D. The resource block is missing a provider configuration.

Solution

1. Step 1: Check naming conflict

   The resource and data source both use the name "main" which causes a naming conflict in Terraform.

2. Step 2: Terraform rules

   Terraform does not allow a resource and a data source to share the same type and name within the same module.

3. Final Answer:

   You cannot use the same name for resource and data source. -> Option C

4. Quick Check:

   Resource and data source names must be unique [OK]

Hint: Resource and data source names must differ [OK]

Common Mistakes:

• Thinking same names cause conflicts
• Believing you always need filters over id
• Assuming data sources can depend on resources
• Blaming missing provider config

5. You want to create a subnet in an existing VPC without recreating the VPC. Which Terraform approach is best?

hard

A. Use a resource block for the VPC and a resource block for the subnet.

B. Use a resource block for the subnet and ignore the VPC.

C. Use a data source block for both VPC and subnet.

D. Use a data source block to read the existing VPC and a resource block to create the subnet.

Solution

1. Step 1: Identify existing infrastructure

   The VPC already exists, so it should not be recreated or managed as a resource.

2. Step 2: Use data source for existing VPC

   Use a data source block to safely read the existing VPC's details without changing it.

3. Step 3: Create subnet resource

   Create a resource block for the subnet to add new infrastructure inside the existing VPC.

4. Final Answer:

   Use a data source block to read the existing VPC and a resource block to create the subnet. -> Option D

5. Quick Check:

   Data source reads existing; resource creates new [OK]

Hint: Read existing with data source; create new with resource [OK]

Common Mistakes:

• Trying to recreate existing VPC as resource
• Using data source to create subnet (not possible)
• Ignoring existing VPC and creating subnet without VPC ID
• Using resource for both causing conflicts