Introduction to Terraform | Terraform Fundamentals

How Terraform Works

Terraform follows a simple workflow:

Write - Define resources in .tf files
Plan - Preview what Terraform will do
Apply - Create, update, or delete resources
Destroy - Clean up when done

Under the hood, Terraform:

Reads your configuration files
Compares desired state to actual state
Calculates the minimal set of changes needed
Executes those changes via cloud provider APIs

Note

Terraform is **declarative**. You describe what you want, not how to create it. Terraform figures out the "how" for you.

Installing Terraform

macOS (with Homebrew)

brew tap hashicorp/tap
brew install hashicorp/tap/terraform

Linux

wget -O- https://apt.releases.hashicorp.com/gpg | sudo gpg --dearmor -o /usr/share/keyrings/hashicorp-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/hashicorp-archive-keyring.gpg] https://apt.releases.hashicorp.com $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/hashicorp.list
sudo apt update && sudo apt install terraform

Verify Installation

terraform version

You should see output like:

Terraform v1.6.0
on darwin_arm64

Your First Configuration

Create a new directory and file:

mkdir terraform-intro && cd terraform-intro

Create main.tf with this content:

terraform {
  required_providers {
    local = {
      source  = "hashicorp/local"
      version = "~> 2.0"
    }
  }
}

resource "local_file" "hello" {
  content  = "Hello, Terraform!"
  filename = "${path.module}/hello.txt"
}

This configuration uses the local provider to create a file. It's perfect for learning without needing cloud credentials.

The Terraform Workflow

Step 1: Initialize

terraform init

This downloads the required providers and sets up your working directory.

Step 2: Plan

terraform plan

Terraform shows you what it will do:

Terraform will perform the following actions:

  # local_file.hello will be created
  + resource "local_file" "hello" {
      + content  = "Hello, Terraform!"
      + filename = "./hello.txt"
      + id       = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Tip

Always review the plan before applying! In production, this prevents accidental destruction of resources.

Step 3: Apply

terraform apply

Terraform asks for confirmation, then creates the resource:

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

local_file.hello: Creating...
local_file.hello: Creation complete after 0s [id=...]

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

Check your directory - hello.txt now exists!

cat hello.txt

Step 4: Destroy (When Done)

terraform destroy

This removes all resources managed by this configuration.

Warning

Be careful with `terraform destroy` in production! It will delete real infrastructure.

Understanding State

Terraform keeps track of what it manages in a state file (terraform.tfstate). This file maps your configuration to real resources.

cat terraform.tfstate

You'll see JSON describing the resources Terraform created.

Danger

Never manually edit the state file! Use `terraform state` commands if you need to modify state.

Practice Exercise

Modify main.tf to change the file content
Run terraform plan - what does it show?
Run terraform apply to update the file
Clean up with terraform destroy

Key Takeaways

Terraform is declarative: describe what you want, not how to build it
The workflow is: init → plan → apply → (eventually) destroy
State tracks the mapping between config and real resources
Always review plans before applying

Next, we'll learn about providers and resources in depth.