Day 5 - Terraform Variables

Before exploring Terraform variables, let’s first understand what variables are.

A variable is simply something whose value can change. Variables are used to avoid hardcoding, improve reusability, enhance readability, and support modular design. Every programming language uses variables and Terraform is no different.

Terraform also supports variables, and they can be categorized in two ways:

• Based on purpose
• Based on value

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1. Input Variables

Used to pass values into Terraform from users or external sources.

Example:

variable "region" {
  type        = string
  default     = "us-east-1"
  description = "AWS region"
}

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2. Output Variables

Used to display or export values after terraform apply.

Example:

output "bucket_name" {
  value = aws_s3_bucket.demo.bucket
}

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3. Local Values (locals)

Used to simplify complex or repeated expressions.

Example:

locals {
  env_name = "dev"
}

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String Concatenation in Terraform

"${var.env}-bucket"

"${var.env}-bucket-${var.region}"

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Terraform Variable Precedence

Terraform loads variables in the following order (LOW to HIGH precedence):

Precedence	Source	Notes
1	Default values in variables.tf	lowest priority
2	Environment variables	export TF_VAR_region="us-east-1"
3	terraform.tfvars	auto-loaded
4	terraform.tfvars.json	auto-loaded
5	**.auto.tfvars / *.auto.tfvars.json*	auto-loaded in alphabetical order
6	-var and -var-file CLI flags	highest priority

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Example Environment Variable

export TF_VAR_env="dev"

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✔ Example CLI Variable

terraform apply -var="env=dev"

✔ Example CLI Var File

terraform apply -var-file="dev.tfvars"

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Example: Creating an S3 Bucket Using env = dev

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variables.tf

variable "env" {
  type        = string
  description = "Environment name"
  default     = "dev"
}

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

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main.tf

provider "aws" {
  region = var.region
}

resource "aws_s3_bucket" "demo" {
  bucket = "${var.env}-bucket-demo"
}

output "bucket_name" {
  value = aws_s3_bucket.demo.bucket
}

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terraform.tfvars (optional)

env = "dev"

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Run Commands

terraform init
terraform plan
terraform apply

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Resulting Bucket Name

dev-bucket-demo

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