生产日志要带上下文：只打印错误不够

// ❌ 每个 handler 内部生成，无法跨服务关联
function handleOrderCreate(req: Request) {
  const localId = crypto.randomUUID()
  logger.info({ localId }, 'creating order')
}
 
// ✅ 在入口中间件生成，注入到请求上下文
app.use((req, res, next) => {
  const requestId = req.headers['x-request-id'] ?? crypto.randomUUID()
  req.context = { requestId }
  next()
})

// ❌ 看不出在做什么
{"level":"error","msg":"query failed","requestId":"abc-123"}
 
// ✅ 模块和操作清晰
{"level":"error","msg":"query failed","requestId":"abc-123","module":"order-service","operation":"createOrder","step":"validateInventory"}

// ❌ 只有错误，没有上下文
logger.error('payment callback processing failed', error)
// 输出：
// {"level":"error","msg":"payment callback processing failed","error":"TypeError: Cannot read property 'amount' of undefined"}
 
// ✅ 带完整上下文
logger.error({
  requestId: ctx.requestId,
  module: 'payment',
  operation: 'handlePaymentCallback',
  provider: 'stripe',
  orderId: order.id,
  userId: order.userId,
  callbackStatus: req.body.status,
  orderStatusBefore: order.status,
  error: error.message,
  stack: error.stack,
}, 'payment callback processing failed')
// 输出：
// {"level":"error","msg":"payment callback processing failed","requestId":"req-7f3a","module":"payment","operation":"handlePaymentCallback","provider":"stripe","orderId":"ord-8821","userId":"usr-4412","callbackStatus":"succeeded","orderStatusBefore":"pending_payment","error":"Cannot read property 'amount' of undefined","stack":"..."}

// ❌ 只知道失败了
logger.error('sync job failed', error)
 
// ✅ 带业务上下文
logger.error({
  module: 'sync-service',
  operation: 'dailyProductSync',
  jobRunId: 'run-20260625-001',
  totalItems: 15000,
  successCount: 23,
  failedCount: 14977,
  firstError: errors[0]?.message,
  firstErrorSku: errors[0]?.sku,
  externalApiStatus: lastApiResponse?.status,
  externalApiLatencyMs: lastApiResponse?.latencyMs,
  durationMs: Date.now() - startTime,
}, 'daily product sync job failed')

// ❌ 只有结果
logger.warn('permission denied', { userId, resourceId })
 
// ✅ 带权限上下文
logger.warn({
  requestId: ctx.requestId,
  module: 'auth',
  operation: 'checkResourceAccess',
  userId: user.id,
  userRole: user.role,
  userTenantId: user.tenantId,
  resourceId: resource.id,
  resourceOwnerId: resource.ownerId,
  resourceTenantId: resource.tenantId,
  permissionRule: 'owner-or-admin',
  matchedRule: 'none',
  crossTenantAccess: user.tenantId !== resource.tenantId,
}, 'permission denied for resource access')

// ❌ 参数校验失败打 error，告警风暴
if (!input.email) {
  logger.error('missing email', { input })
  return res.status(400).json({ error: 'email required' })
}
 
// ✅ 参数校验是预期内的失败，用 warn
if (!input.email) {
  logger.warn('validation failed: missing email', {
    requestId: ctx.requestId,
    module: 'user-service',
    operation: 'createUser',
    validationField: 'email',
  })
  return res.status(400).json({ error: 'email required' })
}
 
// ❌ 外部超时和内部 bug 混在一起
catch (error) {
  logger.error('failed to fetch user profile', error)
}
 
// ✅ 区分外部依赖问题与内部异常
catch (error) {
  if (error instanceof TimeoutError) {
    logger.warn({
      module: 'user-service',
      operation: 'fetchProfile',
      dependency: 'profile-api',
      timeoutMs: 5000,
      retryAttempt: attempt,
    }, 'profile api timeout, will retry')
  } else {
    logger.error({
      requestId: ctx.requestId,
      module: 'user-service',
      operation: 'fetchProfile',
      error: error.message,
      stack: error.stack,
    }, 'unexpected error fetching profile')
  }
}

// ❌ 原始 body 全量记录
logger.info('creating order', { body: req.body })
 
// ✅ 摘要记录关键字段
logger.info({
  requestId: ctx.requestId,
  module: 'order-service',
  operation: 'createOrder',
  itemCount: req.body.items?.length ?? 0,
  totalAmount: req.body.totalAmount,
  currency: req.body.currency,
  // 不记录：收货地址、手机号、支付 token
}, 'creating order')
 
// Token 脱敏工具函数
function maskToken(token: string): string {
  if (!token || token.length < 8) return '***'
  return token.slice(0, 6) + '***'
}

// ❌ 文本格式，难以查询
logger.info(`Order ${orderId} created by user ${userId}, total: ${total}, items: ${itemCount}`)
// 要查某个用户的订单，需要正则匹配，慢且易错
 
// ✅ JSON 结构化，字段可索引
logger.info({
  requestId: ctx.requestId,
  module: 'order-service',
  operation: 'createOrder',
  orderId,
  userId,
  total,
  itemCount,
  durationMs: Date.now() - startTime,
}, 'order created')
// 直接查询：userId="usr-4412" AND operation="createOrder"