Terraform Intermediate: State, Variables & Modules

In this guide, we'll move beyond simple resources and explore how to make your Terraform code reusable, configurable, and robust.

1. Variables (variables.tf)

Hardcoding values is bad practice. Variables allow you to parameterize your configuration.

Defining Variables

Create a variables.tf file:

variable "filename" {
  description = "The name of the file to create"
  type        = string
  default     = "default.txt"
}

variable "content" {
  type    = string
  default = "Hello World"
}

Using Variables

Update your main.tf:

resource "local_file" "example" {
  filename = var.filename
  content  = var.content
}

Passing Values

You can set values in multiple ways (priority order): 1. CLI flags: -var="filename=my-file.txt" 2. terraform.tfvars file:

filename = "prod-config.txt"
content  = "This is production configuration."

3. Environment Variables: TF_VAR_filename="env-file.txt" 4. Defaults (defined in variable block).

2. Outputs (outputs.tf)

Outputs are like return values for your Terraform project. They print useful information to the CLI after an apply.

Create outputs.tf:

output "file_id" {
  value = local_file.example.id
}

After terraform apply, you will see:

Outputs:
file_id = "7c1d..."

3. Data Sources

Data sources allow you to read information that was created outside of Terraform or by another Terraform configuration.

Example: finding the latest Ubuntu AMI in AWS.

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"] # Canonical

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
  }
}

resource "aws_instance" "web" {
  ami           = data.aws_ami.ubuntu.id
  instance_type = "t2.micro"
}

4. Terraform State (terraform.tfstate)

The state file maps your real-world resources to your configuration.

• Local State: Stored by default in terraform.tfstate on your machine. Not recommended for teams.
• Remote State: Stored in a remote backend like S3, Azure Blob Storage, or Terraform Cloud.

Configuring Remote State (S3 Example)

terraform {
  backend "s3" {
    bucket = "my-terraform-state-bucket"
    key    = "dev/terraform.tfstate"
    region = "us-east-1"
  }
}

Note: You must initialize (terraform init) after adding a backend configuration.

5. Modules

Modules are containers for multiple resources that are used together. Every Terraform configuration has at least one module, known as the root module.

Consuming a Public Module

The Terraform Registry hosts thousands of pre-built modules.

Example: Creating a VPC using the official AWS module.

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  name = "my-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["us-east-1a", "us-east-1b"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24"]

  enable_nat_gateway = true
}

---

What's Next?

Ready for the pro level? We'll dive into workspaces, loops, and advanced state management.

👉 Go to Advanced Guide

📬 DevopsPilot Weekly — Learn DevOps, Cloud & Gen AI the simple way.
👉 Subscribe here