Terraform & Infrastructure as Code

Terraform & Infrastructure as Code (IaC)

Expert patterns for managing infrastructure as code với Terraform and modern IaC practices.

When to Use This Skill

• Infrastructure provisioning
• Multi-cloud deployments
• Infrastructure versioning
• Team collaboration on infrastructure
• Disaster recovery setup
• Environment replication

Quick Reference

Terraform Workflow

terraform init    # Initialize working directory
terraform plan    # Preview changes
terraform apply   # Apply changes
terraform destroy # Destroy infrastructure

Basic Terraform Configuration

# main.tf
terraform {
  required_version = ">= 1.0"
  
  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" {
  description = "AWS region"
  type        = string
  default     = "us-east-1"
}

variable "environment" {
  description = "Environment name"
  type        = string
}

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

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

# Outputs
output "vpc_id" {
  description = "VPC ID"
  value       = aws_vpc.main.id
}

Terraform Modules

# modules/web-server/main.tf
resource "aws_instance" "web" {
  ami           = var.ami_id
  instance_type = var.instance_type
  subnet_id     = var.subnet_id
  
  user_data = file("${path.module}/user_data.sh")
  
  tags = {
    Name = var.server_name
  }
}

# modules/web-server/variables.tf
variable "ami_id" {
  type = string
}

variable "instance_type" {
  type    = string
  default = "t3.micro"
}

variable "subnet_id" {
  type = string
}

variable "server_name" {
  type = string
}

# modules/web-server/outputs.tf
output "instance_id" {
  value = aws_instance.web.id
}

output "public_ip" {
  value = aws_instance.web.public_ip
}

# main.tf (using module)
module "web_server" {
  source = "./modules/web-server"
  
  ami_id        = "ami-12345678"
  instance_type = "t3.small"
  subnet_id     = aws_subnet.public[0].id
  server_name   = "production-web"
}

output "web_server_ip" {
  value = module.web_server.public_ip
}

Multi-Cloud Example

# AWS + Google Cloud
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
    google = {
      source  = "hashicorp/google"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = "us-east-1"
}

provider "google" {
  project = "my-project"
  region  = "us-central1"
}

# AWS resources
resource "aws_s3_bucket" "data" {
  bucket = "my-data-bucket"
}

# GCP resources
resource "google_storage_bucket" "backup" {
  name     = "my-backup-bucket"
  location = "US"
}

State Management

# Remote state (S3 backend)
terraform {
  backend "s3" {
    bucket         = "terraform-state"
    key            = "prod/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-locks"
  }
}

# State locking with DynamoDB
resource "aws_dynamodb_table" "terraform_locks" {
  name         = "terraform-locks"
  billing_mode = "PAY_PER_REQUEST"
  hash_key     = "LockID"
  
  attribute {
    name = "LockID"
    type = "S"
  }
}

Workspaces (Multi-Environment)

# Create workspaces
terraform workspace new dev
terraform workspace new staging
terraform workspace new prod

# Switch workspace
terraform workspace select prod

# List workspaces
terraform workspaceist

# Use workspace in config
resource "aws_instance" "app" {
  instance_type = terraform.workspace == "prod" ? "t3.large" : "t3.micro"
  
  tags = {
    Environment = terraform.workspace
  }
}

Testing Infrastructure

# Using Terratest (Go)
package test

import (
    "testing"
    "github.com/gruntwork-io/terratest/modules/terraform"
)

func TestTerraformWebServer(t *testing.T) {
    opts := &terraform.Options{
        TerraformDir: "../modules/web-server",
        Vars: map[string]interface{}{
            "ami_id":     "ami-12345678",
            "subnet_id":  "subnet-123",
            "server_name": "test-server",
        },
    }
    
    defer terraform.Destroy(t, opts)
    terraform.InitAndApply(t, opts)
    
    instanceID := terraform.Output(t, opts, "instance_id")
    // Assert instance exists
}

Import Existing Resources

# Import existing AWS instance
terraform import aws_instance.web i-1234567890abcdef0

# Import into module
terraform import module.web_server.aws_instance.web i-1234567890abcdef0

Best Practices

✅ Use remote state - Team collaboration, state locking
✅ Module everything - Reusable, testable components
✅ Version providers - Avoid breaking changes
✅ Separate environments - Workspaces or separate configs
✅ Use variables - No hardcoded values
✅ Tag all resources - Resource management
✅ Plan before apply - Review changes

Anti-Patterns

❌ Manual changes → State drift
❌ No state locking → Concurrent modification
❌ Hardcoded values → Not reusable
❌ No modules → Duplicate code
❌ Local state only → No collaboration
❌ No versioning → Breaking changes

Related Skills

• kubernetes-patterns - K8s infrastructure
• monitoring-observability - Infrastructure monitoring
• deployment-procedures - Deployment automation

Official Resources

• Terraform Documentation
• Terraform Registry
• Terratest