Serverless vs Traditional Architecture: A Real-World Cost Comparison

resource "aws_instance" "app_server" {
  count           = 2
  instance_type   = "m5.large"
  ami            = data.aws_ami.amazon_linux.id
  
  vpc_security_group_ids = [aws_security_group.app.id]
  subnet_id              = aws_subnet.private[count.index].id
  
  user_data = <<-EOF
    #!/bin/bash
    yum update -y
    yum install -y docker
    systemctl start docker
    docker run -d -p 3000:3000 ${var.app_image}
  EOF
  
  tags = {
    Name = "app-server-${count.index}"
  }
}

resource "aws_db_instance" "postgres" {
  identifier     = "app-database"
  engine         = "postgres"
  engine_version = "13.7"
  instance_class = "db.t3.medium"
  
  allocated_storage     = 100
  storage_encrypted    = true
  
  multi_az               = true
  backup_retention_period = 30
  
  monthly_cost = "$145/month"  # Always running
}

// API Lambda Function
const apiHandler = new NodejsFunction(this, 'ApiHandler', {
  runtime: Runtime.NODEJS_18_X,
  handler: 'handler',
  entry: path.join(__dirname, '../src/api/index.ts'),
  memorySize: 1024,
  timeout: Duration.seconds(30),
  environment: {
    TABLE_NAME: dataTable.tableName,
  },
  bundling: {
    minify: true,
    sourceMap: false,
  }
});

// DynamoDB Table (Pay-per-request)
const dataTable = new Table(this, 'DataTable', {
  billingMode: BillingMode.PAY_PER_REQUEST,
  partitionKey: { name: 'PK', type: AttributeType.STRING },
  sortKey: { name: 'SK', type: AttributeType.STRING },
  pointInTimeRecovery: true,
  stream: StreamViewType.NEW_AND_OLD_IMAGES,
});

// API Gateway
const api = new RestApi(this, 'Api', {
  defaultCorsPreflightOptions: {
    allowOrigins: Cors.ALL_ORIGINS,
    allowMethods: Cors.ALL_METHODS,
  },
  deployOptions: {
    throttlingRateLimit: 1000,
    throttlingBurstLimit: 2000,
  }
});

// Cost: $0 when idle, ~$73/month at 1M requests

// Single Express app handling everything
app.get('/api/products', authenticate, (req, res) => {
  const products = await db.query('SELECT * FROM products');
  res.json(products);
});

app.post('/api/orders', authenticate, async (req, res) => {
  const order = await db.transaction(async (trx) => {
    // Complex order processing logic
    // Inventory management
    // Payment processing
    // Email notifications
  });
  res.json(order);
});

// Running 24/7 on EC2, even at 3 AM with no traffic

// Product Service (Lambda)
export const getProducts = async (event: APIGatewayEvent) => {
  const products = await dynamodb.query({
    TableName: 'Products',
    IndexName: 'category-index',
    KeyConditionExpression: 'category = :cat',
  }).promise();
  
  return {
    statusCode: 200,
    body: JSON.stringify(products.Items),
    headers: { 'Cache-Control': 'max-age=300' }
  };
};

// Order Service (Step Functions + Lambda)
export const processOrder = async (order: Order) => {
  // Step 1: Validate inventory (Lambda)
  // Step 2: Process payment (Lambda)
  // Step 3: Update inventory (Lambda)
  // Step 4: Send confirmation (SQS + Lambda)
  // Each step scales independently
};

// Cost: $0 when no orders, scales to handle Black Friday automatically