Type constraints in variables in Terraform - Mini Project: Build & Apply

Type constraints in variables

📖 Scenario: You are setting up a Terraform configuration to manage cloud resources. To avoid mistakes, you want to define variables with specific type constraints so that only valid values can be used.

🎯 Goal: Build a Terraform configuration that defines variables with type constraints and uses them in a resource configuration.

📋 What You'll Learn

Define a variable with a string type constraint

Define a variable with a list of strings type constraint

Define a variable with a map of numbers type constraint

Use the variables in a resource block

💡 Why This Matters

🌍 Real World

Defining variables with type constraints helps prevent errors when deploying cloud infrastructure by ensuring only valid data is used.

💼 Career

Cloud engineers and DevOps professionals use Terraform variable type constraints to write reliable and maintainable infrastructure code.

1

Define a string variable

Create a Terraform variable called region with type string and default value "us-west-1".

Terraform

# Your code here

Need a hint?

Use the variable block with type = string and set default to "us-west-1".

2

Define a list of strings variable

Add a Terraform variable called availability_zones with type list(string) and default value ["us-west-1a", "us-west-1b"].

Terraform

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

# Your code here

Need a hint?

Use list(string) as the type and set the default to the list of zones.

3

Define a map of numbers variable

Add a Terraform variable called instance_counts with type map(number) and default value { web = 2, db = 1 }.

Terraform

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

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

# Your code here

Need a hint?

Use map(number) as the type and set the default map with keys web and db.

4

Use variables in a resource

Create a Terraform resource aws_instance named web_server that uses the variable region for availability_zone and the variable instance_counts to set count to the value for key web.

Terraform

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

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

variable "instance_counts" {
  type    = map(number)
  default = {
    web = 2
    db  = 1
  }
}

# Your code here

Need a hint?

Use count = var.instance_counts["web"] and availability_zone = var.region inside the resource block.