构建分布式令牌桶

项目概述

本项目实现一个面向 distributed rate limiting 的完整系统，核心要解决的问题是 enforcing a global rate limit across multiple instances without a centralized bottleneck。整体由 Local bucket、Remote sync、Refill scheduler、Bias compensation、Fallback limiter 五个模块组成，每个模块单一职责、可独立测试，最后通过集成测试验证端到端正确性。设计上把 clock skew between instances that lets each refill slightly faster than the global rate and overshoots the limit 作为第一类需求先行处理，而非事后再补。

架构与关键决策

数据模型为 a local token count that refills over time and periodically syncs against a shared counter, with bias to avoid over-granting。Local bucket 定义其余阶段共同依赖的数据形状并在边界处校验输入；Remote sync 承载 distributed rate limiting 的正确性逻辑；Refill scheduler 专门处理 clock skew between instances that lets each refill slightly faster than the global rate and overshoots the limit，在失败路径上给出明确的拒绝、重试或降级策略；Bias compensation 提供可观测性，每次操作输出带关联 id 的结构化事件；Fallback limiter 在过载时按既定方式降级，避免过载演变为数据损坏。配置与代码分离，使风险变更可经 diff 审阅。

实施与测试

按五个阶段依次实现 Local bucket、Remote sync、Refill scheduler、Bias compensation、Fallback limiter，每阶段配套聚焦单测。集成测试组合各模块并驱动真实 distributed rate limiting 场景：先验证正常路径，再刻意触发 clock skew between instances that lets each refill slightly faster than the global rate and overshoots the limit 并断言系统降级而非损坏。所有依赖均在进程内或被桩替换，用例在 CI 中确定可复现。

限制与后续

• 单区域设计，多区域复制超出范围。
• Local bucket 默认进程内，未水平共享。
• 无鉴权层，假定部署在强制身份的边缘之后。

代码示例

# setup for token-bucket-distributed
pnpm init
pnpm add redis fastify
pnpm add -D typescript tsx vitest

token_bucket_distributed/
├── src/index.ts
├── src/local-bucket.ts
├── src/remote-sync.ts
├── tests/token_bucket_distributed.test.ts
└── package.json

// Local bucket: distributed rate limiting core
export function localbucket(input: LocalbucketInput): LocalbucketResult {
  // Build the local bucket that anchors distributed rate limiting and defines the core data shape.
  return processLocalbucket(input);
}

// Remote sync — handles distributed rate limiting Add the remote sync so
export class Remotesync {
  constructor(private opts: RemotesyncOptions) {}
  async run(ctx: Context): Promise<RemotesyncOutput> {
    return this.execute(ctx);
  }
}

// Refill scheduler: distributed rate limiting stage
export const refillscheduler = (next: Next) => async (req: Request) => {
  const out = await transform(req);
  return next(out);
};

// Bias compensation for distributed rate limiting
export async function biascompensation(stream: AsyncIterable<Chunk>): Promise<Aggregate> {
  let acc = init();
  for await (const c of stream) acc = merge(acc, c);
  return acc;
}

// Fallback limiter: distributed rate limiting finalization
export function fallbacklimiter(state: State): Result {
  validate(state);
  return finalize(state);
}

# run the distributed rate limiting test suite
pnpm vitest run