构建 DNS 解析缓存

项目概述

本项目实现一个面向 dns resolution 的完整系统，核心要解决的问题是 caching resolved records with correct TTL handling and negative caching to avoid hammering upstream resolvers。整体由 Record cache、TTL scheduler、Negative cache、Prefetch warmer、Resolution pipeline 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 a popular name whose TTL expires simultaneously across many instances and produces a thundering herd of lookups 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 cache of DNS records keyed by name and type, each entry expiring at its TTL with negative answers cached briefly。Record cache 定义其余阶段共同依赖的数据形状并在边界处校验输入；TTL scheduler 承载 dns resolution 的正确性逻辑；Negative cache 专门处理 a popular name whose TTL expires simultaneously across many instances and produces a thundering herd of lookups，在失败路径上给出明确的拒绝、重试或降级策略；Prefetch warmer 提供可观测性，每次操作输出带关联 id 的结构化事件；Resolution pipeline 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 Record cache、TTL scheduler、Negative cache、Prefetch warmer、Resolution pipeline，每阶段配套聚焦单测。集成测试组合各模块并驱动真实 dns resolution 场景：先验证正常路径，再刻意触发 a popular name whose TTL expires simultaneously across many instances and produces a thundering herd of lookups 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。
• Record cache 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 dns-resolver-cache
pnpm init
pnpm add dns-packet dgram
pnpm add -D typescript tsx vitest

dns_resolver_cache/
├── src/index.ts
├── src/record-cache.ts
├── src/ttl-scheduler.ts
├── tests/dns_resolver_cache.test.ts
└── package.json

// Record cache: dns resolution core
export function recordcache(input: RecordcacheInput): RecordcacheResult {
  // Build the record cache that anchors dns resolution and defines the core data shape.
  return processRecordcache(input);
}

// TTL scheduler — handles dns resolution Add the ttl scheduler so
export class Ttlscheduler {
  constructor(private opts: TtlschedulerOptions) {}
  async run(ctx: Context): Promise<TtlschedulerOutput> {
    return this.execute(ctx);
  }
}

// Negative cache: dns resolution stage
export const negativecache = (next: Next) => async (req: Request) => {
  const out = await transform(req);
  return next(out);
};

// Prefetch warmer for dns resolution
export async function prefetchwarmer(stream: AsyncIterable<Chunk>): Promise<Aggregate> {
  let acc = init();
  for await (const c of stream) acc = merge(acc, c);
  return acc;
}

// Resolution pipeline: dns resolution finalization
export function resolutionpipeline(state: State): Result {
  validate(state);
  return finalize(state);
}

# run the dns resolution test suite
pnpm vitest run