Terraform Practical Guide | IaC· AWS

Why Terraform?

Without Infrastructure as Code, cloud setups are:

• Manual (click in the console → can’t reproduce exactly)
• Undocumented (no record of what was created or why)
• Error-prone (different settings in dev vs prod)
• Slow to recreate (hours of clicking vs minutes of terraform apply)

Terraform solves all of this by describing your infrastructure in code:

Manual:            Click → Create → Forget → Can't reproduce

With Terraform:    Write HCL → terraform plan → terraform apply → Git commit
                   Reproducible, documented, version-controlled, team-reviewable

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Installation

# macOS
brew install terraform

# Linux
sudo apt update && sudo apt install terraform

# Windows
choco install terraform

# Verify
terraform version
# Terraform v1.7.x

---

Core Concepts

Configuration (.tf files)
  ↓ terraform init      Downloads providers
  ↓ terraform plan      Shows what will change
  ↓ terraform apply     Creates/modifies resources
  ↓ terraform destroy   Destroys all resources

State file (.tfstate)
  Tracks what Terraform actually created
  Stores resource IDs, attributes, dependencies
  Must be stored remotely (S3) for teams

Term	What it is
Provider	Plugin for a cloud platform (AWS, GCP, Azure)
Resource	A cloud resource to create (EC2, S3, VPC)
Data source	Read existing resources without managing them
Variable	Input parameter for reusable configs
Output	Value exposed after apply (IP address, ARN)
Module	Reusable group of resources
State	Record of what Terraform has created

---

Your First Terraform Config

# main.tf

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

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

resource "aws_s3_bucket" "my_bucket" {
  bucket = "my-terraform-bucket-unique-12345"

  tags = {
    Name        = "My Terraform Bucket"
    Environment = "dev"
    ManagedBy   = "Terraform"
  }
}

# Initialize — downloads the AWS provider
terraform init

# Preview what will be created
terraform plan

# Create the resources
terraform apply          # Prompts for confirmation
terraform apply -auto-approve  # Skip confirmation (use in CI only)

# Check current state
terraform show

# Destroy everything (⚠️ irreversible)
terraform destroy

---

Variables

Define Variables

# variables.tf

variable "region" {
  description = "AWS region to deploy into"
  type        = string
  default     = "us-east-1"
}

variable "environment" {
  description = "Deployment environment (dev, staging, prod)"
  type        = string

  validation {
    condition     = contains(["dev", "staging", "prod"], var.environment)
    error_message = "Must be dev, staging, or prod."
  }
}

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t3.micro"
}

variable "common_tags" {
  description = "Tags to apply to all resources"
  type        = map(string)
  default = {
    ManagedBy = "Terraform"
    Project   = "MyApp"
  }
}

Use Variables

# main.tf

provider "aws" {
  region = var.region
}

resource "aws_instance" "web" {
  ami           = data.aws_ami.ubuntu.id
  instance_type = var.instance_type

  tags = merge(var.common_tags, {
    Name        = "web-server"
    Environment = var.environment
  })
}

Set Variable Values

# CLI
terraform apply -var="environment=prod" -var="instance_type=t3.medium"

# terraform.tfvars (auto-loaded)
environment   = "prod"
instance_type = "t3.medium"
region        = "us-east-1"

common_tags = {
  ManagedBy = "Terraform"
  Project   = "MyApp"
  Team      = "Platform"
}

---

Outputs

# outputs.tf

output "web_server_public_ip" {
  description = "Public IP of the web server"
  value       = aws_instance.web.public_ip
}

output "s3_bucket_arn" {
  description = "ARN of the S3 bucket"
  value       = aws_s3_bucket.my_bucket.arn
}

output "rds_endpoint" {
  description = "RDS connection endpoint"
  value       = aws_db_instance.main.endpoint
  sensitive   = true   # Hides value in terminal output
}

terraform output                        # All outputs
terraform output web_server_public_ip   # Specific output
terraform output -json                  # JSON format (for scripts)

---

Real-World: VPC + EC2 + Security Group

# vpc.tf

resource "aws_vpc" "main" {
  cidr_block           = "10.0.0.0/16"
  enable_dns_hostnames = true
  enable_dns_support   = true

  tags = { Name = "${var.environment}-vpc" }
}

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_internet_gateway" "main" {
  vpc_id = aws_vpc.main.id
  tags   = { Name = "${var.environment}-igw" }
}

resource "aws_route_table" "public" {
  vpc_id = aws_vpc.main.id

  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = aws_internet_gateway.main.id
  }
}

resource "aws_route_table_association" "public" {
  count          = 2
  subnet_id      = aws_subnet.public[count.index].id
  route_table_id = aws_route_table.public.id
}

# ec2.tf

resource "aws_security_group" "web" {
  name        = "${var.environment}-web-sg"
  description = "Web server security group"
  vpc_id      = aws_vpc.main.id

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["YOUR_IP/32"]   # Restrict SSH to your IP
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_instance" "web" {
  ami                    = data.aws_ami.ubuntu.id
  instance_type          = var.instance_type
  subnet_id              = aws_subnet.public[0].id
  vpc_security_group_ids = [aws_security_group.web.id]
  key_name               = aws_key_pair.deployer.key_name

  user_data = <<-EOF
    #!/bin/bash
    apt update -y
    apt install -y nginx
    systemctl start nginx
    systemctl enable nginx
    echo "Hello from Terraform — ${var.environment}" > /var/www/html/index.html
  EOF

  tags = { Name = "${var.environment}-web-server" }
}

---

Remote State (Required for Teams)

Never use local state for team projects. Use S3 + DynamoDB for atomic, encrypted remote state:

# First, create the state bucket manually (one-time setup)
aws s3 mb s3://my-terraform-state-bucket --region us-east-1
aws s3api put-bucket-versioning \
  --bucket my-terraform-state-bucket \
  --versioning-configuration Status=Enabled

# Create DynamoDB table for state locking
aws dynamodb create-table \
  --table-name terraform-state-lock \
  --attribute-definitions AttributeName=LockID,AttributeType=S \
  --key-schema AttributeName=LockID,KeyType=HASH \
  --billing-mode PAY_PER_REQUEST

# backend.tf

terraform {
  backend "s3" {
    bucket         = "my-terraform-state-bucket"
    key            = "prod/terraform.tfstate"   # Path within bucket
    region         = "us-east-1"
    dynamodb_table = "terraform-state-lock"     # Prevents concurrent applies
    encrypt        = true
  }
}

# State management commands
terraform state list                           # List all resources in state
terraform state show aws_instance.web          # Show resource details
terraform state mv aws_instance.old aws_instance.new  # Rename resource
terraform state rm aws_instance.unwanted       # Remove from state (keeps real resource)
terraform import aws_instance.web i-1234567890  # Import existing resource

---

Modules — Reusable Infrastructure

Define a Module

# modules/vpc/variables.tf
variable "environment" { type = string }
variable "cidr_block" { type = string }
variable "public_subnet_cidrs" { type = list(string) }

# modules/vpc/main.tf
resource "aws_vpc" "main" {
  cidr_block           = var.cidr_block
  enable_dns_hostnames = true
  tags = { Name = "${var.environment}-vpc" }
}

# modules/vpc/outputs.tf
output "vpc_id" { value = aws_vpc.main.id }
output "public_subnet_ids" { value = aws_subnet.public[*].id }

Use the Module

# main.tf

module "vpc" {
  source = "./modules/vpc"

  environment         = "production"
  cidr_block          = "10.0.0.0/16"
  public_subnet_cidrs = ["10.0.1.0/24", "10.0.2.0/24"]
}

resource "aws_instance" "web" {
  subnet_id = module.vpc.public_subnet_ids[0]  # Use module output
}

Terraform Registry Modules

# Use a community module from registry.terraform.io
module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "~> 5.0"

  name = "production-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["us-east-1a", "us-east-1b"]
  public_subnets  = ["10.0.1.0/24", "10.0.2.0/24"]
  private_subnets = ["10.0.11.0/24", "10.0.12.0/24"]

  enable_nat_gateway = true
}

---

Workspaces — Multiple Environments

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

# Switch workspaces
terraform workspace select prod

# Show current workspace
terraform workspace show    # prod

# List workspaces
terraform workspace list
# * prod
#   dev
#   staging

Use workspace in configuration:

locals {
  env = terraform.workspace

  instance_config = {
    dev     = { type = "t3.micro",  count = 1 }
    staging = { type = "t3.small",  count = 2 }
    prod    = { type = "t3.medium", count = 3 }
  }
}

resource "aws_instance" "web" {
  count         = local.instance_config[local.env].count
  instance_type = local.instance_config[local.env].type
}

---

CI/CD Integration (GitHub Actions)

# .github/workflows/terraform.yml
name: Terraform

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

env:
  TF_VAR_environment: ${{ github.ref == 'refs/heads/main' && 'prod' || 'dev' }}

jobs:
  terraform:
    runs-on: ubuntu-latest
    permissions:
      id-token: write    # For OIDC authentication
      contents: read
      pull-requests: write

    steps:
      - uses: actions/checkout@v4

      - uses: hashicorp/setup-terraform@v3
        with:
          terraform_version: 1.7.x

      - name: Configure AWS Credentials (OIDC — no long-lived keys)
        uses: aws-actions/configure-aws-credentials@v4
        with:
          role-to-assume: arn:aws:iam::123456789:role/GitHubActionsRole
          aws-region: us-east-1

      - name: Terraform Init
        run: terraform init

      - name: Terraform Plan
        id: plan
        run: terraform plan -no-color -out=tfplan
        continue-on-error: true

      - name: Post Plan as PR Comment
        uses: actions/github-script@v7
        if: github.event_name == 'pull_request'
        with:
          script: |
            const output = `#### Terraform Plan 📖\`${{ steps.plan.outcome }}\`
            <details><summary>Show Plan</summary>

            \`\`\`
            ${{ steps.plan.outputs.stdout }}
            \`\`\`

            </details>`;
            github.rest.issues.createComment({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              body: output
            })

      - name: Terraform Apply (main branch only)
        if: github.ref == 'refs/heads/main' && github.event_name == 'push'
        run: terraform apply tfplan

---

Best Practices

File structure:

infrastructure/
├── main.tf           # Main resources
├── variables.tf      # Input variables
├── outputs.tf        # Output values
├── backend.tf        # Remote state config
├── data.tf           # Data sources
├── terraform.tfvars  # Variable values (not committed for secrets)
└── modules/
    ├── vpc/
    ├── ec2/
    └── rds/

Rules:

1. Always use remote state for teams
2. Never commit .tfvars with secrets — use AWS Secrets Manager or environment variables
3. Run terraform plan before every apply — review the diff
4. Tag all resources with Environment, ManagedBy = "Terraform", and Project
5. Pin provider versions (~> 5.0) to avoid surprise upgrades
6. Use terraform fmt to format code and terraform validate to check syntax
7. Store state per environment (dev/terraform.tfstate, prod/terraform.tfstate)

Related posts:

• AWS Beginner’s Guide
• GitHub Actions CI/CD Guide
• Docker & Kubernetes Guide

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Frequently Asked Questions (FAQ)

Q. When would I use this in practice?

A. Manage cloud infrastructure as code with Terraform. Covers HCL syntax, AWS resource provisioning (VPC, EC2, S3, RDS), re…

Q. What should I read before this?

A. Follow the previous article or related articles links at the bottom of each post to learn in sequence.

Q. Where can I study this more deeply?

A. Check cppreference and the relevant library’s official documentation. The reference links at the end of the article are also worth using.

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Related Articles (Internal Links)

Other articles related to this topic.

• AWS 입문 가이드 | EC2, S3, RDS 실전 사용법
• Docker & Kubernetes 입문 가이드 | 컨테이너부터 오케스트레이션까지
• GitHub Actions 완벽 가이드 | CI/CD·자동화·Workflow·배포·실전 활용

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Keywords Covered in This Article (Related Search Terms)

This article covers Terraform, IaC, AWS, DevOps, Infrastructure, Cloud, Automation.