Introduction to Terraform

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Chapter objectives

• Understand Infrastructure as Code
• Discover Terraform and its concepts
• Compare with the alternatives
• Identify use cases

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1 - What is Infrastructure as Code?

The traditional problem

The IaC solution

Advantages of IaC

Manual approach	Infrastructure as Code
Clicks in the console	Versioned code
Outdated documentation	Code = documentation
Hard to reproduce	Identical deployment
Complex audit	Git history
Slow and error-prone	Fast and reliable

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2 - What is Terraform?

Definition

Terraform is an open-source HashiCorp tool for provisioning and managing infrastructure declaratively.

Key characteristics

Characteristic	Description
Declarative	You describe the desired final state
Agnostic	Works with 3000+ providers
Idempotent	Same result on every run
State	Tracking of the infrastructure state
Plan	Preview of the changes

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3 - Terraform workflow

The 4 essential commands

Command details

Command	Action	When to use it
init	Initializes the project	At the start, after adding a provider
plan	Previews the changes	Before each apply
apply	Applies the changes	To create/modify
destroy	Removes the infrastructure	To clean up

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4 - Fundamental concepts

Architecture

Main components

Component	Description	Example
Provider	Plugin to communicate with an API	aws, azurerm, google
Resource	Infrastructure element to create	aws_instance, azurerm_virtual_machine
Data Source	Reading of existing data	aws_ami, azurerm_subscription
Variable	Input parameter	instance_type, region
Output	Exported value	public_ip, dns_name
Module	Reusable group of resources	vpc-module, ecs-cluster
State	File tracking the infrastructure	terraform.tfstate

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5 - Declarative vs Imperative

Imperative approach (scripts)

# Script bash
aws ec2 run-instances \
  --image-id ami-12345678 \
  --instance-type t2.micro \
  --count 1

# Si on relance, on crée une 2ème instance !

Declarative approach (Terraform)

# Configuration Terraform
resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"
}

# Relancer = pas de changement si l'instance existe déjà

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6 - Comparison with the alternatives

IaC tools

Comparison table

Criterion	Terraform	CloudFormation	Ansible	Pulumi
Type	Provisioning	Provisioning	Config	Provisioning
Multi-cloud	✅ Yes	❌ AWS only	✅ Yes	✅ Yes
Language	HCL	JSON/YAML	YAML	Python/TS/Go
State	External	Managed by AWS	None	External
Curve	Medium	Medium	Easy	Hard
License	BSL	Proprietary	GPL	Apache

When to use Terraform?

Use case	Terraform	Alternative
Multi-cloud	✅ Excellent	-
AWS only	✅ Good	CloudFormation
Server configuration	⚠️ Possible	Ansible
Kubernetes	✅ Good	Helm, ArgoCD
Developers	⚠️ HCL	Pulumi (languages)

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7 - HashiCorp ecosystem

HashiCorp products

Terraform Cloud

Feature	OSS	Cloud Free	Cloud Team
Local execution	✅	✅	✅
Remote state	❌	✅	✅
Collaboration	❌	❌	✅
Sentinel policies	❌	❌	✅
SSO	❌	❌	✅

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8 - First example

Configuration file

# main.tf

# Configuration du provider AWS
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = "eu-west-1"
}

# Créer une instance EC2
resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"

  tags = {
    Name = "HelloTerraform"
  }
}

# Afficher l'IP publique
output "public_ip" {
  value = aws_instance.web.public_ip
}

Execution

# Initialiser le projet
terraform init

# Prévisualiser
terraform plan

# Appliquer
terraform apply

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

Outputs:
public_ip = "54.123.45.67"

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Summary

Key points

• Terraform turns infrastructure into code
• Declarative approach: describe the final state
• Multi-cloud: AWS, Azure, GCP and more
• The state tracks the actual state of the infrastructure
• Plan before apply: always preview

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Practical exercises

1. Explain the difference between IaC and traditional scripts
2. Name 3 advantages of Terraform
3. What is the role of the state file?
4. Compare Terraform and Ansible

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