Om's Brain

7 Terraform Variable

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📘 **Terraform Variables

⭐ 1. Input Variables (variable)

Used to pass values into Terraform.

variable "environment" {
  default = "dev"
  type    = string
}

Use them as:

var.environment

⭐ 2. Output Variables (output)

Used to print/export values after resources are created.

Example:

output "vpc_id" {
  value = aws_vpc.sample.id
}

View output anytime:

terraform output

⭐ 3. Local Variables (locals)

Used for internal calculation, concatenation, and reusable values.

locals {
  bucket_name = "${var.project}-bucket-${var.environment}"
}

Use as:

local.bucket_name

Types of Variables (Based on Value / Type Constraints)

  • Primitive Types — string, number, bool
  • Complex Types — list(), set(), map(), object(), tuple()
  • Special Types — any, null

How to Set Variable Values (Precedence Order)

From lowest → highest priority:

1️⃣ Default value inside variable block

default = "dev"

2️⃣ Environment variable

export TF_VAR_environment=stage

3️⃣ *terraform.tfvars / .auto.tfvars

environment = "preprod"

4️⃣ -var flag (highest priority)

terraform plan -var="environment=prod"

👉 Last one wins (overrides everything else).

Best Practices

✔ Use variables.tf → store all input variables
✔ Use local.tf → store locals
✔ Use outputs.tf → store outputs
✔ Use terraform.tfvars for environment-specific values
✔ Never hard-code secrets in variables → use SSM / Secrets Manager

Summary

  • Input variables take values
  • Local variables compute reusable values
  • Output variables export values
  • Many ways to set values → precedence decides final value
  • Use variables to avoid repetition & support multi-environment deployment

Graph View