Variable declaration syntax in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic syntax to declare a variable in Terraform?

Use the variable block with a name and optional attributes like type, default, and description.

Example:

variable "region" {
  type = string
  default = "us-west-1"
  description = "AWS region to deploy resources"
}

beginner

What does the default attribute do in a Terraform variable declaration?

It sets a value that Terraform uses if no other value is provided when running.

This makes the variable optional because it has a fallback value.

intermediate

How do you specify the type of a variable in Terraform?

Use the type attribute inside the variable block.

Common types: string, number, bool, list(string), map(string).

Example:

variable "ports" {
  type = list(number)
}

beginner

Can you declare a variable without a default value in Terraform? What happens then?

Yes, you can declare a variable without a default.

Terraform will require you to provide a value when you run your configuration, or it will show an error.

beginner

How do you add a description to a Terraform variable and why is it useful?

Use the description attribute inside the variable block.

This helps others (and yourself) understand what the variable is for.

Example:

variable "env" {
  type = string
  description = "The environment to deploy to, e.g., dev or prod"
}

Which block is used to declare a variable in Terraform?

A variable

B resource

C output

D provider

The variable block is used to declare variables in Terraform.

What happens if you declare a variable without a default value and do not provide a value when running Terraform?

A Terraform uses a random value

B Terraform uses an empty string

C Terraform throws an error and stops

D Terraform ignores the variable

Terraform requires a value for variables without defaults; otherwise, it throws an error.

How do you specify that a variable should be a list of strings?

A type = string[]

B type = list(string)

C type = array

D type = map(string)

Terraform uses list(string) to specify a list of strings.

Which attribute is used to provide a fallback value for a variable?

A value

B initial

C fallback

D default

The default attribute sets a fallback value for a variable.

Why is adding a description to a variable useful?

A It documents the variable's purpose

B It changes the variable's value

C It makes the variable required

D It encrypts the variable

Descriptions help explain the purpose of variables to users.

Explain how to declare a variable in Terraform including type, default, and description.

Think about the structure of a variable block and what each attribute does.

What happens if you declare a variable without a default and do not provide a value when running Terraform?

Consider Terraform's behavior when required inputs are missing.

Practice

1. What is the purpose of declaring a variable in Terraform?

easy

A. To write comments in the Terraform file

B. To create a new resource in the cloud

C. To define the output of a Terraform plan

D. To store values that can be reused and customized in the configuration

Solution

1. Step 1: Understand variable role in Terraform

   Variables hold values that can be changed without editing the main code, making it flexible.

2. Step 2: Compare with other options

   Creating resources, defining outputs, or comments are different Terraform features, not variable declaration.

3. Final Answer:

   To store values that can be reused and customized in the configuration -> Option D

4. Quick Check:

   Variables = reusable values [OK]

Hint: Variables hold reusable values to customize code easily [OK]

Common Mistakes:

• Confusing variables with resources
• Thinking variables define outputs
• Using variables as comments

2. Which of the following is the correct syntax to declare a string variable named region with a default value of us-west-1 in Terraform?

easy

A. variable region = "us-west-1"

B. var region = "us-west-1"

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

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

Solution

1. Step 1: Recall Terraform variable declaration syntax

   Variables use the block format: variable "name" { type = TYPE default = VALUE } with quotes around strings.

2. Step 2: Check each option

   variable "region" { type = string default = "us-west-1" } matches correct syntax with proper quotes and order. Options B and C are invalid syntax. variable "region" { default = us-west-1 type = string } misses quotes around default value.

3. Final Answer:

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

4. Quick Check:

   Correct block syntax with quotes [OK]

Hint: Use variable block with quotes and type before default [OK]

Common Mistakes:

• Missing quotes around string values
• Using assignment (=) outside variable block
• Incorrect order or missing type keyword

3. Given this variable declaration in Terraform:

variable "instance_count" {
  type    = number
  default = 3
}

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

medium

A. 3

B. null

C. 0

D. Error: variable not set

Solution

1. Step 1: Identify default value in variable block

   The variable instance_count has a default value set to 3.

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

   If no value is provided during plan or apply, Terraform uses the default value.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Default value used when no override = 3 [OK]

Hint: Default value applies if no input given [OK]

Common Mistakes:

• Assuming default is zero if not set
• Expecting error without override
• Confusing null with default

4. Identify the error in this Terraform variable declaration:

variable "enable_logging" {
  type = bool
  default = "true"
}

medium

A. The default value should not be in quotes for bool type

B. The type should be string, not bool

C. The variable name is invalid

D. Missing description field

Solution

1. Step 1: Check type and default value compatibility

   The variable type is bool, so the default must be a boolean value, not a string.

2. Step 2: Identify the error in default value

   The default is "true" (a string), but it should be true (boolean without quotes).

3. Final Answer:

   The default value should not be in quotes for bool type -> Option A

4. Quick Check:

   Boolean default must be unquoted true/false [OK]

Hint: Boolean defaults must be unquoted true or false [OK]

Common Mistakes:

• Putting boolean default in quotes
• Confusing string and bool types
• Ignoring type mismatch errors

5. You want to declare a variable tags in Terraform that holds a map of strings with a default value of {"env" = "prod", "team" = "devops"}. Which is the correct declaration?

hard

A. variable "tags" { type = map(string) default = { env = prod, team = devops } }

B. variable "tags" { type = map(string) default = { "env" = "prod", "team" = "devops" } }

C. variable "tags" { type = map default = { "env" = "prod", "team" = "devops" } }

D. variable "tags" { type = map(string) default = ["env" = "prod", "team" = "devops"] }

Solution

1. Step 1: Understand map type syntax in Terraform

   Maps of strings use type = map(string) and string values must be quoted.

2. Step 2: Check default value format

   Default must be a map with quoted string values inside curly braces, not square brackets.

3. Step 3: Evaluate options

   variable "tags" { type = map(string) default = { "env" = "prod", "team" = "devops" } } correctly uses type = map(string) and default with quoted values. variable "tags" { type = map(string) default = { env = prod, team = devops } } misses quotes on values, variable "tags" { type = map default = { "env" = "prod", "team" = "devops" } } misses string type, variable "tags" { type = map(string) default = ["env" = "prod", "team" = "devops"] } uses square brackets (list) incorrectly.

4. Final Answer:

   variable "tags" { type = map(string) default = { "env" = "prod", "team" = "devops" } } -> Option B

5. Quick Check:

   Map(string) with quoted string values in braces [OK]

Hint: Use map(string) type and quoted string values in braces [OK]

Common Mistakes:

• Missing quotes on map values
• Using map without specifying string type
• Using list syntax instead of map