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Infrastructure as Code (IaC) with Terraform ​

Cloud infrastructure today is far too complex to manage by hand. Infrastructure as Code (IaC) brings software engineering practices to infrastructure: automation, version control, repeatability, and modular design. Among all IaC tools, Terraform has become the industry standard thanks to its cloud-agnostic design and strong ecosystem.

This guide covers Terraform fundamentals, a practical AWS example, and the interview-ready patterns you’ll need to explain in FAANG interviews or apply in real-world engineering.

Terraform

1. Why IaC with Terraform? ​

  • Definition: Manage infrastructure using code instead of manual clicks.
  • Benefits: Consistency, repeatability, automation, modularity.
  • Alternatives: AWS CloudFormation, Azure ARM templates, Pulumi.
  • Why Terraform: Cloud-agnostic, strong ecosystem of providers, open-source, declarative.

2. Core Terraform Concepts ​

  • HCL (HashiCorp Configuration Language): Declarative syntax for resources.
  • Providers: Plugins for AWS, GCP, Azure, OCI, Kubernetes, etc.
  • State: Tracks the real-world infrastructure (terraform.tfstate).
  • Modules: Reusable building blocks for cleaner, DRY infrastructure.
  • Workflow:
    1. terraform init — initialize.
    2. terraform plan — preview changes.
    3. terraform apply — create/update resources.
    4. terraform destroy — clean up.

3. Practical Example: AWS VPC + EC2 + S3 ​

A minimal Terraform example to create a VPC, subnet, EC2 instance, and S3 bucket.

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

# Variables for customization
variable "bucket_name" {
  type    = string
  default = "my-terraform-bucket-example"
}

# VPC
resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
  tags = { Name = "main-vpc" }
}

# Subnet
resource "aws_subnet" "public" {
  vpc_id     = aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
  tags = { Name = "public-subnet" }
}

# EC2 Instance
resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0" # Amazon Linux 2
  instance_type = "t2.micro"
  subnet_id     = aws_subnet.public.id
  tags = { Name = "web-server" }
}

# S3 Bucket
resource "aws_s3_bucket" "data" {
  bucket = var.bucket_name
  acl    = "private"
  tags   = { Name = "data-bucket" }
}

# Outputs
output "instance_ip" {
  value = aws_instance.web.public_ip
}
output "bucket_name" {
  value = aws_s3_bucket.data.bucket
}

Best practices:

  • Store credentials in ~/.aws/credentials or use IAM roles, never inline.
  • Split into modules for larger projects (e.g., vpc, compute, storage).
  • Use remote state (e.g., S3 + DynamoDB lock) for teams.
  • Add lifecycle rules and tags for cost visibility.

4. Terraform in Distributed Systems ​

Terraform is used to provision:

  • Compute: EC2, GKE nodes, OCI compute.
  • Networking: VPCs, load balancers, firewalls.
  • Storage: S3, GCS, OCI Object Storage.
  • Databases: RDS, Cloud SQL, DynamoDB.

In distributed systems design:

  • Use modules for repeatable patterns (e.g., web service stack).
  • Environment isolation: dev / stage / prod.
  • CI/CD integration: Run terraform plan and terraform apply in pipelines.

5. Common Terraform Patterns ​

  • Modular architecture: Reusable modules for VPC, DB, app clusters.
  • Remote state: Store in S3/GCS/Azure Blob with locking.
  • Workspaces: Manage environments (dev, staging, prod).
  • GitOps workflow: PR → review → pipeline → terraform apply.
  • Secrets: Use cloud-native secrets managers, not inline variables.

6. Interview & Real-World Tips ​

  • Know the basics: service mapping (EC2 ⇄ Compute Engine ⇄ OCI Compute).
  • Explain scaling: stateless services, autoscaling, LB.
  • Discuss security: IAM roles, least privilege, encryption.
  • Trade-offs: Manual vs automated, cost vs availability.
  • Concrete examples: S3 bucket with lifecycle rules, or Terraform module reuse.
  • STAR format: Be ready with one story of IaC automation → cost savings / faster deployment.

Example response:

“I automated VPC + EC2 + S3 provisioning with Terraform, reducing deployment time from 2 days to 30 minutes and cutting costs 15% by adding S3 lifecycle rules.”

7. Final Notes ​

Terraform + IaC is a must-know skill for interviews and real-world cloud engineering. Master:

  • Service mapping (compute, storage, networking).
  • Terraform workflow (init, plan, apply).
  • Patterns: modular design, state management, remote backends.

Next: Containerization: Docker and Kubernetes