A Practical Guide to Adopting Serverless Architecture

import boto3
from PIL import Image
import io

def handler(event, context):
    s3 = boto3.client('s3')

    bucket = event['Records'][0]['s3']['bucket']['name']
    key = event['Records'][0]['s3']['object']['key']

    # 원본 이미지 다운로드
    response = s3.get_object(Bucket=bucket, Key=key)
    image = Image.open(io.BytesIO(response['Body'].read()))

    # 썸네일 생성 (200x200)
    image.thumbnail((200, 200), Image.LANCZOS)

    buffer = io.BytesIO()
    image.save(buffer, format='JPEG', quality=85)
    buffer.seek(0)

    s3.put_object(
        Bucket=bucket,
        Key=f"thumbnails/{key}",
        Body=buffer.getvalue(),
        ContentType='image/jpeg'
    )
    return {'statusCode': 200}

# serverless.yml
provider:
  name: aws
  runtime: python3.12
  architecture: arm64  # Graviton: 20% 저렴
  memorySize: 512
  timeout: 30

functions:
  thumbnail:
    handler: handler.handler
    events:
      - s3:
          bucket: my-bucket
          event: s3:ObjectCreated:*
          rules:
            - prefix: uploads/
            - suffix: .jpg

Cold Start 시간:
- Python 3.12: ~300ms
- Node.js 20: ~200ms
- Go 1.21: ~50ms

# 전역 초기화 (컨테이너 재사용)
s3 = boto3.client('s3')      # 1회만 초기화

def handler(event, context):
    response = s3.get_object(...)  # 재사용

# Provisioned Concurrency로 Cold Start 제거
functions:
  api:
    provisionedConcurrency: 5  # 5개 인스턴스 항상 웜