Terraform Variables

In Terraform, a variable is a way to parameterize your configuration so you can reuse the same code with different inputs instead of hardcoding values.

Think of variables like function arguments in programming—they let you pass data into your Terraform configuration.

🔹 Basic Example

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t2.micro"
}

You can then use it like this:

resource "aws_instance" "example" {
  ami           = "ami-123456"
  instance_type = var.instance_type
}

🔹 Key Components

A variable block can include:

type → Defines expected data type (string, number, bool, list, map, etc.)
default → Optional fallback value
description → Helps document usage
validation → Optional rules for allowed values

Example with validation:

variable "environment" {
  type = string

  validation {
    condition     = contains(["dev", "prod"], var.environment)
    error_message = "Environment must be dev or prod."
  }
}

🔹 Ways to Assign Values

Terraform variables can be set in multiple ways (priority order):

Command line flags

terraform apply -var="instance_type=t3.medium"

.tfvars file
```
instance_type = "t3.large"
```
Environment variables
```
export TF_VAR_instance_type="t3.small"
```
Default value (inside the variable block)

🔹 Types of Variables

Terraform supports rich types:

variable "example" {
  type = object({
    name = string
    age  = number
  })
}

🔹 Why Use Variables?

Reuse configurations across environments (dev, staging, prod)
Avoid hardcoding values
Make modules flexible and portable

🔹 Quick Analogy

Terraform variables = inputs to your infrastructure code Terraform outputs = results returned from that code