Default values in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a default value in Terraform variables?

A default value is a preset value assigned to a variable. It is used when no other value is provided during deployment.

beginner

How do you define a default value for a variable in Terraform?

Use the 'default' argument inside the variable block. For example:

variable "region" {
  type    = string
  default = "us-west-1"
}

beginner

What happens if you do not provide a value for a variable without a default in Terraform?

Terraform will prompt you to enter a value during deployment because it has no default to fall back on.

beginner

Why are default values useful in Terraform configurations?

They simplify deployments by providing common values automatically, reducing the need for manual input every time.

intermediate

Can default values be overridden in Terraform? How?

Yes, default values can be overridden by providing a value through command line flags, environment variables, or variable files.

What keyword is used to set a default value for a variable in Terraform?

A default

B value

C set

D initial

The 'default' keyword assigns a default value to a variable in Terraform.

If a variable has a default value, what happens when you do not provide a value during deployment?

A Terraform prompts for input

B Terraform uses the default value

C Terraform throws an error

D Terraform skips the variable

Terraform automatically uses the default value if no other value is provided.

Which of these is NOT a way to override a default variable value in Terraform?

A Passing a command line flag

B Setting an environment variable

C Using a variable file

D Editing the Terraform binary

Editing the Terraform binary is not a valid way to override variable values.

What type of variable must you provide a value for if it has no default?

A Required variable

B Optional variable

C Output variable

D Local variable

Variables without defaults are required and must be given a value.

Why might you want to use default values in Terraform variables?

A To disable variables

B To make deployment slower

C To reduce manual input and simplify deployment

D To prevent any changes to variables

Default values help reduce manual input and make deployments easier.

Explain how default values work in Terraform variables and why they are helpful.

Think about what happens if you don't provide a value.

Describe the ways you can override a default variable value in Terraform.

Consider different methods to provide values when running Terraform.

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