程序员练级攻略：分布式架构工程设计-[2026重制版]

# ❌ 错误：硬编码配置
# database:
#   host: localhost
#   port: 3306

# ✅ 正确：使用环境变量
database:
  host: ${DB_HOST:localhost}
  port: ${DB_PORT:3306}
  password: ${DB_PASSWORD}   # 绝不提交密码到代码库！

import logging
import json
from datetime import datetime

# 结构化JSON日志（推荐）
logger = logging.getLogger(__name__)

def handle_request(request):
    logger.info(json.dumps({
        "timestamp": datetime.utcnow().isoformat(),
        "level": "INFO",
        "service": "user-service",
        "trace_id": request.headers.get("X-Trace-ID"),
        "user_id": request.user.id,
        "action": "get_profile",
        "duration_ms": 42,
        "status_code": 200
    }))

# 输出到stdout，让基础设施收集
# docker logs / kubectl logs 即可查看

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: api-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: api-server
  minReplicas: 3
  maxReplicas: 100
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 70
  - type: Pods
    pods:
      metric:
        name: http_requests_per_second
      target:
        type: AverageValue
        averageValue: "1000"
  behavior:
    scaleUp:
      stabilizationWindowSeconds: 60
      policies:
      - type: Percent
        value: 100
        periodSeconds: 15
    scaleDown:
      stabilizationWindowSeconds: 300
      policies:
      - type: Percent
        value: 10
        periodSeconds: 60

import redis
import json

r = redis.Redis(host='cache', port=6379, db=0)

def get_user(user_id):
    # 1. 先查缓存
    cache_key = f"user:{user_id}"
    cached = r.get(cache_key)
    
    if cached:
        return json.loads(cached)  # Cache Hit
    
    # 2. 缓存未命中，查数据库
    user = db.query("SELECT * FROM users WHERE id = %s", user_id)
    
    if user:
        # 3. 写入缓存（设置过期时间）
        r.setex(cache_key, 3600, json.dumps(user))  # TTL = 1小时
    
    return user  # Cache Miss

月度SLO = 99.9% → 允许停机时间 = 43.2分钟
已用停机 = 10分钟 → 剩余预算 = 33.2分钟