🏗️ Terraform & Infrastructure as Code (IaC)

HashiCorp HCL Syntax, Declarative Cloud Provisioning, State Management (Locking & Backends), Modules, Workspaces aur Multi-Cloud Automation ka complete guide.

Curriculum Index

1. Module 1: What is IaC & Declarative vs Imperative Approaches
2. Module 2: HashiCorp Configuration Language (HCL) Primitives
3. Module 3: The 4-Step Core Workflow (init, plan, apply, destroy)
4. Module 4: Terraform State Architecture (State Drift & Locking)
5. Module 5: Remote Backends (AWS S3 + DynamoDB State Locking)
6. Module 6: Reusable Terraform Modules & Variable Types
7. Module 7: Environment Management with Terraform Workspaces

Module 01

1️⃣ What is IaC & Declarative vs Imperative

Definition: Infrastructure as Code (IaC) cloud servers, networks, load balancers aur databases ko cloud console par manually click karne ke bajay machine-readable configuration code files ke zariye automatically build, update aur version-control karne ki process hai.

Criteria	Declarative (Terraform, CloudFormation)	Imperative (Ansible, Bash, Python SDK)
Philosophy	"What" – Desired final state define karo.	"How" – Step-by-step commands specify karo.
State Tracking	Current state track karke delta (diff) calculate karta hai.	Scripts bina existing state dekhe execute hoti hain.
Idempotency	100% strictly idempotent by design.	Custom scripting ke bina repeat run par duplicate ban sakta hai.

Module 02

2️⃣ HashiCorp Configuration Language (HCL) Primitives

HCL human-readable aur machine-friendly declarative language hai:

# 1. Provider Declaration
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = var.aws_region
}

# 2. Resource Block
resource "aws_instance" "web_server" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type

  tags = {
    Name        = "Production-Web-Node"
    Environment = "Prod"
  }
}

# 3. Output Block
output "public_ip" {
  description = "Public IP address of the newly provisioned EC2 instance"
  value       = aws_instance.web_server.public_ip
}

Module 03

3️⃣ The 4-Step Core Workflow

Command	Internal Operation
terraform init	Working directory initialize karta hai, required cloud provider plugins download karta hai.
terraform plan	Desired state vs Real state compare karke execution graph (Add, Change, Destroy) preview karta hai.
terraform apply	Cloud APIs call karke actual infrastructure create ya modify karta hai aur state file update karta hai.
terraform destroy	Configuration file me defined sabhi cloud resources ko securely delete karta hai.

Live Terraform Core CLI Execution Engine Simulator

[Terraform Core]: Ready. Directory contains main.tf. Run `terraform init` to initialize provider plugins...

Module 04

4️⃣ Terraform State Architecture & Drift Detection

State File (terraform.tfstate): Ek JSON file jo aapke written HCL code aur cloud me actually bane physical resources ke beech direct mapping record karti hai.

State Drift: Jab koi developer cloud console me jakar manually resource modify ya delete kar deta hai, toh code aur real-world me antar aa jata hai. Terraform terraform plan run karte hi state refresh karke is drift ko detect kar leta hai aur original state restore karta hai.

Module 05

5️⃣ Remote Backends & State Locking

Production environments me state file ko local disk par rakhna dangerous hota hai (Accidental loss ya merge conflict risk):

# Backend configuration using AWS S3 & DynamoDB
terraform {
  backend "s3" {
    bucket         = "company-tf-state-prod"
    key            = "global/s3/terraform.tfstate"
    region         = "ap-south-1"
    dynamodb_table = "terraform-state-locks" # Enforces State Locking!
    encrypt        = true
  }
}

State Locking: Agar do DevOps engineers ek sath terraform apply chalayein, toh DynamoDB table state ko lock kar deta hai taaki file corrupt na ho.

Module 06

6️⃣ Reusable Terraform Modules

DRY (Don't Repeat Yourself) principle follow karne ke liye standardized components build karna:

# Calling a custom VPC module
module "vpc_networking" {
  source             = "./modules/aws-vpc"
  vpc_cidr           = "10.0.0.0/16"
  public_subnets     = ["10.0.1.0/24", "10.0.2.0/24"]
  environment_tag    = "Staging"
}

Module 07

7️⃣ Multi-Environment Management with Workspaces

# 1. List all available workspaces
terraform workspace list

# 2. Create and switch to staging
terraform workspace new staging
terraform workspace select staging

# 3. Dynamic resource sizing based on current workspace
resource "aws_instance" "app" {
  instance_type = terraform.workspace == "prod" ? "t3.xlarge" : "t3.micro"
}