서버리스 도입 가이드: 적합한 워크로드·한도·관측

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

# AWS Lambda 동시성·스로틀 확인
aws cloudwatch get-metric-statistics \
  --namespace AWS/Lambda --metric-name Throttles \
  --dimensions Name=FunctionName,Value=my-fn \
  --start-time $(date -u -d '1 hour ago' +%Y-%m-%dT%H:%M:%SZ) \
  --end-time $(date -u +%Y-%m-%dT%H:%M:%SZ) \
  --period 60 --statistics Sum

# 계정 동시성 한도와 함수 설정
aws lambda get-account-settings --query 'AccountLimit.ConcurrentExecutions'
aws lambda get-function-configuration --function-name thumb --query '{timeout:Timeout,mem:MemorySize}'
# 최근 1시간 스로틀·오류 지표
aws cloudwatch get-metric-statistics --namespace AWS/Lambda --metric-name Throttles \
  --dimensions Name=FunctionName,Value=thumb --statistics Sum --period 300 \
  --start-time $(date -u -d '-1 hour' +%FT%TZ) --end-time $(date -u +%FT%TZ)
# 타임아웃 로그
aws logs filter-log-events --log-group-name /aws/lambda/thumb --filter-pattern '"Task timed out"'