Terraform for Multi-Cloud IaC: HCL, State & Modular Architectures

Developed by HashiCorp, Terraform is the undisputed industry standard tool for building, changing, and versioning cloud infrastructure safely and efficiently. Unlike vendor-locked tools (such as CloudFormation for AWS or ARM/Bicep for Azure), Terraform is cloud-agnostic, allowing engineers to manage AWS, Azure, Google Cloud, Cloudflare, GitHub, and Kubernetes clusters using a unified declarative syntax called HashiCorp Configuration Language (HCL).

The Core Terraform Workflow (Init, Plan, Apply, Destroy)

1. terraform init: Initializes the working directory containing Terraform configuration files. Downloads necessary cloud provider plugins (e.g., hashicorp/aws) and configures the remote backend.
2. terraform plan: Reads the current state file, refreshes live cloud infrastructure via APIs, calculates the difference (diff), and generates an execution plan outlining exactly what will be created (+), modified (~), or destroyed (-).
3. terraform apply: Prompts for human confirmation, then executes the planned API calls against the cloud provider in the correct dependency order. Updates the state file upon completion.
4. terraform destroy: Safely tears down and deletes all resources managed by the configuration file (ideal for temporary testing environments).

Production Remote State Management (S3 + DynamoDB Locking)

In professional engineering teams, storing the terraform.tfstate file on a developer's local laptop is a critical anti-pattern. If two developers run terraform apply simultaneously, the state file corrupts. Production Terraform requires a Remote Backend with State Locking:

# backend.tf - Production Remote State with S3 and DynamoDB Locking
terraform {
  required_version = ">= 1.5.0"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }

  backend "s3" {
    bucket         = "veewom-terraform-state-prod"
    key            = "vpc/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-state-locks" # Prevents concurrent applies!
  }
}

Example: Provisioning an AWS VPC with Terraform HCL

# main.tf - Declarative VPC & Subnet
resource "aws_vpc" "main" {
  cidr_block           = "10.0.0.0/16"
  enable_dns_hostnames = true
  enable_dns_support   = true

  tags = {
    Name        = "Veewom-Production-VPC"
    Environment = "production"
    ManagedBy   = "Terraform"
  }
}

resource "aws_subnet" "public_1" {
  vpc_id                  = aws_vpc.main.id
  cidr_block              = "10.0.1.0/24"
  availability_zone       = "us-east-1a"
  map_public_ip_on_launch = true

  tags = {
    Name = "Veewom-Public-Subnet-1"
  }
}