Infrastructure as Code with Terraform: AWS Complete Guide

Terraform enables you to define cloud infrastructure as code, ensuring consistency and repeatability across environments.

Basic AWS Infrastructure

# main.tf
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
  
  backend "s3" {
    bucket = "my-terraform-state"
    key    = "prod/terraform.tfstate"
    region = "us-east-1"
  }
}

provider "aws" {
  region = var.aws_region
}

# Variables
variable "aws_region" {
  default = "us-east-1"
}

variable "environment" {
  default = "production"
}

# VPC
resource "aws_vpc" "main" {
  cidr_block           = "10.0.0.0/16"
  enable_dns_hostnames = true
  enable_dns_support   = true
  
  tags = {
    Name        = "${var.environment}-vpc"
    Environment = var.environment
  }
}

# Subnets
resource "aws_subnet" "public" {
  count             = 2
  vpc_id            = aws_vpc.main.id
  cidr_block        = "10.0.${count.index + 1}.0/24"
  availability_zone = data.aws_availability_zones.available.names[count.index]
  
  map_public_ip_on_launch = true
  
  tags = {
    Name = "${var.environment}-public-${count.index + 1}"
  }
}

resource "aws_subnet" "private" {
  count             = 2
  vpc_id            = aws_vpc.main.id
  cidr_block        = "10.0.${count.index + 10}.0/24"
  availability_zone = data.aws_availability_zones.available.names[count.index]
  
  tags = {
    Name = "${var.environment}-private-${count.index + 1}"
  }
}

EC2 with Auto Scaling

# ec2.tf
resource "aws_launch_template" "app" {
  name_prefix   = "${var.environment}-app"
  image_id      = data.aws_ami.amazon_linux.id
  instance_type = "t3.medium"
  
  vpc_security_group_ids = [aws_security_group.app.id]
  
  user_data = base64encode(<<-EOF
    #!/bin/bash
    yum update -y
    yum install -y docker
    systemctl start docker
    docker run -d -p 80:8080 my-app:latest
  EOF
  )
  
  iam_instance_profile {
    name = aws_iam_instance_profile.app.name
  }
  
  tags = {
    Environment = var.environment
  }
}

resource "aws_autoscaling_group" "app" {
  name                = "${var.environment}-app-asg"
  vpc_zone_identifier = aws_subnet.private[*].id
  desired_capacity    = 2
  min_size            = 1
  max_size            = 10
  
  launch_template {
    id      = aws_launch_template.app.id
    version = "$Latest"
  }
  
  target_group_arns = [aws_lb_target_group.app.arn]
  
  tag {
    key                 = "Name"
    value               = "${var.environment}-app"
    propagate_at_launch = true
  }
}

# Auto Scaling Policy
resource "aws_autoscaling_policy" "scale_up" {
  name                   = "scale-up"
  autoscaling_group_name = aws_autoscaling_group.app.name
  adjustment_type        = "ChangeInCapacity"
  scaling_adjustment     = 1
  cooldown               = 300
}

RDS Database

# rds.tf
resource "aws_db_instance" "main" {
  identifier           = "${var.environment}-db"
  engine               = "postgres"
  engine_version       = "15.4"
  instance_class       = "db.t3.medium"
  allocated_storage    = 20
  max_allocated_storage = 100
  
  db_name  = "myapp"
  username = var.db_username
  password = var.db_password
  
  vpc_security_group_ids = [aws_security_group.db.id]
  db_subnet_group_name   = aws_db_subnet_group.main.name
  
  backup_retention_period = 7
  backup_window          = "03:00-04:00"
  maintenance_window     = "Mon:04:00-Mon:05:00"
  
  multi_az               = true
  deletion_protection    = true
  skip_final_snapshot    = false
  
  tags = {
    Environment = var.environment
  }
}

Modules for Reusability

# modules/vpc/main.tf
variable "cidr_block" {}
variable "environment" {}

resource "aws_vpc" "this" {
  cidr_block = var.cidr_block
  tags = { Name = "${var.environment}-vpc" }
}

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

# Usage in main.tf
module "vpc" {
  source      = "./modules/vpc"
  cidr_block  = "10.0.0.0/16"
  environment = "production"
}

Terraform Commands

# Initialize
terraform init

# Plan changes
terraform plan -out=tfplan

# Apply changes
terraform apply tfplan

# Destroy infrastructure
terraform destroy

# Format code
terraform fmt -recursive

# Validate configuration
terraform validate

# Import existing resources
terraform import aws_instance.example i-1234567890abcdef0

Terraform makes infrastructure reproducible and version-controlled. Start with modules for maintainability!