Default values in Terraform - Mini Project: Build & Apply

Terraform Default Values

📖 Scenario: You are setting up a simple Terraform configuration to create cloud resources. You want to use variables with default values so that the configuration works even if no values are provided by the user.

🎯 Goal: Build a Terraform configuration that defines a variable with a default value and uses it to create a resource with that default unless overridden.

📋 What You'll Learn

Define a Terraform variable with a default value

Use the variable in a resource configuration

Ensure the configuration is valid and deployable

💡 Why This Matters

🌍 Real World

Using default values in Terraform variables allows cloud infrastructure to be flexible and reusable without requiring users to always provide input.

💼 Career

Cloud engineers and DevOps professionals often use Terraform variables with defaults to create modular and easy-to-maintain infrastructure code.

1

Define a variable with a default value

Create a Terraform variable called instance_type with the default value t2.micro.

Terraform

# Define the variable 'instance_type' with default 't2.micro'
# Your code here

Hint

Use the variable block with default to set a default value.

2

Add a provider configuration

Add a Terraform provider block for AWS with the region set to us-east-1.

Terraform

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

# Add AWS provider with region 'us-east-1'
# Your code here

Hint

The provider block configures the cloud provider and region.

3

Create an EC2 instance resource using the variable

Create a resource block called aws_instance named example that uses the variable instance_type for its instance_type attribute and sets ami to ami-0c55b159cbfafe1f0.

Terraform

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

provider "aws" {
  region = "us-east-1"
}

# Create aws_instance resource named 'example' using variable 'instance_type' and AMI 'ami-0c55b159cbfafe1f0'
# Your code here

Hint

Use var.instance_type to reference the variable inside the resource.

4

Add an output to show the instance type

Add an output block called instance_type_output that outputs the value of the variable instance_type.

Terraform

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type
}

# Add output 'instance_type_output' to show variable 'instance_type'
# Your code here

Hint

Use an output block to display values after deployment.

Practice

1. What is the purpose of setting a default value for a variable in Terraform?

easy

A. To make the variable mandatory without a fallback

B. To provide a fallback value if no other value is given

C. To disable the variable completely

D. To automatically generate a random value

Solution

1. Step 1: Understand variable defaults in Terraform

   Default values act as fallback values when no input is provided by the user.

2. Step 2: Identify the purpose of default values

   They make variables optional and provide a safe, predictable value.

3. Final Answer:

   To provide a fallback value if no other value is given -> Option B

4. Quick Check:

   Default value = fallback [OK]

Hint: Default means fallback if no input given [OK]

Common Mistakes:

• Thinking default makes variable mandatory
• Assuming default disables the variable
• Believing default auto-generates random values

2. Which of the following is the correct syntax to set a default value for a variable named region in Terraform?

easy

A. variable "region" { default = "us-east-1" }

B. variable region { default: "us-east-1" }

C. var region = default "us-east-1"

D. variable "region" = "us-east-1"

Solution

1. Step 1: Recall Terraform variable block syntax

   Variables are declared with the keyword variable and a name in quotes.

2. Step 2: Check correct default assignment

   The default value is set inside the block with default = "value".

3. Final Answer:

   variable "region" { default = "us-east-1" } -> Option A

4. Quick Check:

   Correct syntax uses variable block and default = value [OK]

Hint: Use variable "name" { default = "value" } [OK]

Common Mistakes:

• Missing quotes around variable name
• Using colon instead of equals for default
• Assigning default outside variable block

3. Given this variable declaration:

variable "instance_type" {
  default = "t2.micro"
}

What will be the value of var.instance_type if no override is provided?

medium

A. null

B. Error: variable not set

C. empty string ""

D. "t2.micro"

Solution

1. Step 1: Identify the default value in the variable block

   The variable instance_type has a default set to "t2.micro".

2. Step 2: Understand behavior when no override is given

   If no value is provided, Terraform uses the default value automatically.

3. Final Answer:

   "t2.micro" -> Option D

4. Quick Check:

   Default used if no override [OK]

Hint: No override? Use default value [OK]

Common Mistakes:

• Assuming null if no value given
• Expecting error without override
• Thinking default is empty string

4. You wrote this variable block:

variable "env" {
  default: "production"
}

Why does Terraform give a syntax error?

medium

A. Because default uses colon instead of equals sign

B. Because variable name must not be in quotes

C. Because default value must be a number

D. Because variable blocks cannot have defaults

Solution

1. Step 1: Check the syntax for default assignment

   Terraform requires = to assign default values, not a colon.

2. Step 2: Identify the cause of syntax error

   Using default: "production" causes a syntax error because colon is invalid here.

3. Final Answer:

   Because default uses colon instead of equals sign -> Option A

4. Quick Check:

   Use = not : for default [OK]

Hint: Use = for default, not colon : [OK]

Common Mistakes:

• Using colon instead of equals for default
• Removing quotes from variable name
• Thinking default must be numeric

5. You want to create a variable availability_zones with a default list of zones ["us-east-1a", "us-east-1b"]. Which is the correct way to declare it in Terraform?

hard

A. variable "availability_zones" {
default = "us-east-1a, us-east-1b"
}

B. variable availability_zones = ["us-east-1a", "us-east-1b"]

C. variable "availability_zones" {
type = list(string)
default = ["us-east-1a", "us-east-1b"]
}

D. variable "availability_zones" {
type = string
default = ["us-east-1a", "us-east-1b"]
}

Solution

1. Step 1: Define variable with correct type for list of strings

   Use type = list(string) to specify a list of strings.

2. Step 2: Assign default as a list of strings

   Set default = ["us-east-1a", "us-east-1b"] inside the variable block.

3. Final Answer:

   variable "availability_zones" { type = list(string) default = ["us-east-1a", "us-east-1b"] } -> Option C

4. Quick Check:

   List type with list default [OK]

Hint: Use type list(string) and default list [OK]

Common Mistakes:

• Omitting type for list variables
• Assigning list to string type
• Using string with commas instead of list