构建特性开关服务

项目概述

本项目实现一个面向 feature toggling 的完整系统，核心要解决的问题是 serving flag evaluations with targeting rules and gradual rollouts without a flag change becoming a deploy。整体由 Flag store、Rule evaluator、Rollout bucket、Snapshot cache、Change watcher 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 rollout hash that clusters identifiers and gives one cohort far more traffic than the percentage implies 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 set of flags each with rules keyed by attribute, plus a rollout percentage evaluated by hashing an identifier into a bucket。Flag store 定义其余阶段共同依赖的数据形状并在边界处校验输入；Rule evaluator 承载 feature toggling 的正确性逻辑；Rollout bucket 专门处理 a rollout hash that clusters identifiers and gives one cohort far more traffic than the percentage implies，在失败路径上给出明确的拒绝、重试或降级策略；Snapshot cache 提供可观测性，每次操作输出带关联 id 的结构化事件；Change watcher 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 Flag store、Rule evaluator、Rollout bucket、Snapshot cache、Change watcher，每阶段配套聚焦单测。集成测试组合各模块并驱动真实 feature toggling 场景：先验证正常路径，再刻意触发 a rollout hash that clusters identifiers and gives one cohort far more traffic than the percentage implies 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。
• Flag store 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 feature-toggle-service
pnpm init
pnpm add fastify redis xxhash-wasm
pnpm add -D typescript tsx vitest

feature_toggle_service/
├── src/index.ts
├── src/flag-store.ts
├── src/rule-evaluator.ts
├── tests/feature_toggle_service.test.ts
└── package.json

// Flag store: feature toggling core
export function flagstore(input: FlagstoreInput): FlagstoreResult {
  // Build the flag store that anchors feature toggling and defines the core data shape.
  return processFlagstore(input);
}

// Rule evaluator — handles feature toggling Add the rule evaluator so
export class Ruleevaluator {
  constructor(private opts: RuleevaluatorOptions) {}
  async run(ctx: Context): Promise<RuleevaluatorOutput> {
    return this.execute(ctx);
  }
}

// Rollout bucket: feature toggling stage
export const rolloutbucket = (next: Next) => async (req: Request) => {
  const out = await transform(req);
  return next(out);
};

// Snapshot cache for feature toggling
export async function snapshotcache(stream: AsyncIterable<Chunk>): Promise<Aggregate> {
  let acc = init();
  for await (const c of stream) acc = merge(acc, c);
  return acc;
}

// Change watcher: feature toggling finalization
export function changewatcher(state: State): Result {
  validate(state);
  return finalize(state);
}

# run the feature toggling test suite
pnpm vitest run