Data source block syntax in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a data block in Terraform?

A data block lets you fetch information from existing resources outside your Terraform configuration. It helps you use data created elsewhere.

beginner

What are the main parts of a Terraform data source block?

A data source block has three parts: the keyword data, the resource type (like aws_ami), and a name you choose to reference it later.

beginner

How do you reference a data source output in Terraform?

Use data.<resource_type>.<name>.<attribute>. For example, data.aws_ami.example.id gets the AMI ID.

intermediate

Example: What does this data block do?

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"]
  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
  }
}

It finds the most recent Ubuntu 20.04 AMI owned by the official Ubuntu account. This lets you use the latest Ubuntu image in your infrastructure.

beginner

Why use data sources instead of hardcoding values?

Data sources keep your config flexible and up-to-date. They fetch live info, so you avoid errors from outdated or manual values.

What keyword starts a data source block in Terraform?

A data

B resource

C variable

D output

The data keyword defines a data source block to fetch existing info.

How do you name a data source block?

A You use the resource type only

B You use the provider name

C You provide a unique name after the resource type

D You don't name data sources

You give a unique name after the resource type to reference the data source later.

Which of these is a valid way to reference a data source attribute?

A output.aws_instance.example.id

B data.aws_instance.example.id

C var.aws_instance.example.id

D resource.aws_instance.example.id

Data source attributes are referenced with data.<type>.<name>.<attribute>.

What does the filter block inside a data source do?

A It sets variables

B It creates a new resource

C It deletes resources

D It filters which existing resources to fetch

Filters narrow down which existing resources the data source returns.

Why is using data sources considered a best practice?

A They fetch live data to keep configs current

B They hardcode values for stability

C They speed up Terraform runs

D They replace variables

Data sources fetch live info, avoiding stale or manual values.

Explain the structure and purpose of a Terraform data source block.

Think about how you tell Terraform to look up info it doesn't create.

Describe how filters work inside a data source block and why they are useful.

Filters help you find exactly what you need from many options.

Practice

1. What is the main purpose of a data source block in Terraform?

easy

A. To create new cloud resources from scratch

B. To define variables for Terraform configuration

C. To delete existing cloud resources

D. To read information about existing cloud resources without creating new ones

Solution

1. Step 1: Understand the role of data sources

   Data sources in Terraform are used to fetch information about existing resources, not to create or delete them.

2. Step 2: Compare options with this role

   Only To read information about existing cloud resources without creating new ones describes reading existing resource info without creation, matching the data source purpose.

3. Final Answer:

   To read information about existing cloud resources without creating new ones -> Option D

4. Quick Check:

   Data source = read existing info [OK]

Hint: Data sources read existing resources, not create or delete [OK]

Common Mistakes:

• Confusing data sources with resource blocks
• Thinking data sources create resources
• Assuming data sources delete resources

2. Which of the following is the correct syntax to define a data source block for an AWS AMI in Terraform?

easy

A. data "aws_ami" example { filter { name = "name" values = ["my-ami"] } }

B. resource "aws_ami" "example" { filter { name = "name" values = ["my-ami"] } }

C. data "aws_ami" "example" { filter { name = "name" values = ["my-ami"] } }

D. data aws_ami example { filter { name = "name" values = ["my-ami"] } }

Solution

1. Step 1: Identify correct block type and syntax

   Data source blocks start with data, followed by resource type and local name in quotes.

2. Step 2: Check each option

   data "aws_ami" "example" { filter { name = "name" values = ["my-ami"] } } uses correct quotes and block structure. resource "aws_ami" "example" { filter { name = "name" values = ["my-ami"] } } uses resource instead of data. Options A and C miss quotes around local name or resource type.

3. Final Answer:

   data "aws_ami" "example" { filter { name = "name" values = ["my-ami"] } } -> Option C

4. Quick Check:

   Data source syntax = data "type" "name" { ... } [OK]

Hint: Data source block uses data "type" "name" with quotes [OK]

Common Mistakes:

• Using resource instead of data
• Omitting quotes around type or name
• Incorrect block nesting or missing braces

3. Given this Terraform data source block:

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

What will data.aws_vpc.selected.id return?

medium

A. The ID of the VPC tagged with Name=main-vpc

B. The name tag value main-vpc

C. A list of all VPC IDs in the AWS account

D. An error because filter syntax is invalid

Solution

1. Step 1: Understand the filter block

   The filter selects the VPC resource with tag Name equal to main-vpc.

2. Step 2: Identify the returned attribute

   data.aws_vpc.selected.id accesses the ID of the matched VPC, not the tag value or a list.

3. Final Answer:

   The ID of the VPC tagged with Name=main-vpc -> Option A

4. Quick Check:

   Filter selects resource, .id returns its ID [OK]

Hint: Filter narrows resource, .id returns its unique ID [OK]

Common Mistakes:

• Confusing tag value with resource ID
• Expecting a list instead of single ID
• Assuming filter syntax is wrong

4. Identify the error in this Terraform data source block:

data "aws_subnet" "example" {
  filter {
    name = "availability-zone"
    values = "us-west-2a"
  }
}

medium

A. The values attribute should be a list, not a string

B. The filter block is missing a closing brace

C. The data source type aws_subnet does not support filters

D. The local name example must be uppercase

Solution

1. Step 1: Check the values attribute type

   In Terraform, filter values must be a list, even if only one value is given.

2. Step 2: Verify the given values

   The code uses a string instead of a list, which causes a syntax error.

3. Final Answer:

   The values attribute should be a list, not a string -> Option A

4. Quick Check:

   Filter values = list, not string [OK]

Hint: Always use list syntax ["value"] for filter values [OK]

Common Mistakes:

• Using string instead of list for values
• Assuming filter block needs no braces
• Thinking local name case matters

5. You want to use a data source block to get the latest Amazon Linux 2 AMI ID filtered by owner and name pattern. Which of these blocks correctly achieves this?

hard

A. resource "aws_ami" "latest" {
most_recent = true
owners = ["amazon"]
filter {
name = "name"
values = ["amzn2-ami-hvm-*-x86_64-gp2"]
}
}

B. data "aws_ami" "latest" {
most_recent = true
owners = ["amazon"]
filter {
name = "name"
values = ["amzn2-ami-hvm-*-x86_64-gp2"]
}
}

C. data "aws_ami" "latest" {
filter {
name = "owner"
values = ["amazon"]
}
filter {
name = "name"
values = ["amzn2-ami-hvm-*-x86_64-gp2"]
}
}

D. data "aws_ami" "latest" {
most_recent = true
owner = "amazon"
filter {
name = "name"
values = ["amzn2-ami-hvm-*-x86_64-gp2"]
}
}

Solution

1. Step 1: Confirm correct block type and attributes

   Use data block for reading AMI info, with most_recent = true and owners as a list.

2. Step 2: Check filter and owner syntax

   data "aws_ami" "latest" { most_recent = true owners = ["amazon"] filter { name = "name" values = ["amzn2-ami-hvm-*-x86_64-gp2"] } } correctly uses owners list and a filter for name pattern. data "aws_ami" "latest" { filter { name = "owner" values = ["amazon"] } filter { name = "name" values = ["amzn2-ami-hvm-*-x86_64-gp2"] } } incorrectly filters owner as a filter. resource "aws_ami" "latest" { most_recent = true owners = ["amazon"] filter { name = "name" values = ["amzn2-ami-hvm-*-x86_64-gp2"] } } uses resource block instead of data. data "aws_ami" "latest" { most_recent = true owner = "amazon" filter { name = "name" values = ["amzn2-ami-hvm-*-x86_64-gp2"] } } uses singular owner instead of owners list.

3. Final Answer:

   data "aws_ami" "latest" { most_recent = true owners = ["amazon"] filter { name = "name" values = ["amzn2-ami-hvm-*-x86_64-gp2"] } } -> Option B

4. Quick Check:

   Use data block, owners list, most_recent true [OK]

Hint: Use owners list and most_recent true in data block [OK]

Common Mistakes:

• Using resource block instead of data
• Filtering owner instead of using owners attribute
• Using singular owner instead of owners list