高可用架构设计

class CanaryDeployment {
  constructor() {
    this.stable = { version: 'v1.0.0', weight: 90 };
    this.canary = { version: 'v2.0.0', weight: 10 };
  }

  route(userId) {
    const hash = this.hashCode(userId) % 100;
    return hash < this.canary.weight ? this.canary.version : this.stable.version;
  }

  monitor() {
    const errorRate = this.getErrorRate('canary');
    if (errorRate > 0.05) this.rollback(); // 错误率 > 5% 自动回滚
  }

  rollback() {
    this.canary.weight = 0;
    this.stable.weight = 100;
  }
}

class MultiDataCenter {
  constructor() {
    this.dcs = {
      beijing:  { status: 'active', weight: 30 },
      shanghai: { status: 'active', weight: 30 },
      guangzhou:{ status: 'active', weight: 40 }
    };
  }

  failover(failedDC) {
    const failedWeight = this.dcs[failedDC].weight;
    this.dcs[failedDC].status = 'failed';
    this.dcs[failedDC].weight = 0;

    const active = Object.keys(this.dcs).filter(k => this.dcs[k].status === 'active');
    const extra = failedWeight / active.length;
    active.forEach(dc => { this.dcs[dc].weight += extra; });
  }
}

class CircuitBreaker {
  constructor(threshold = 5, timeout = 60000) {
    this.states = new Map();
    this.threshold = threshold;
    this.timeout = timeout;
  }

  isOpen(service) {
    const s = this.states.get(service);
    if (!s || s.status !== 'open') return false;
    if (Date.now() - s.lastFailure > this.timeout) {
      s.status = 'half-open'; // 半开：允许试探性请求
      return false;
    }
    return true;
  }

  recordFailure(service) {
    const s = this.states.get(service) || { status: 'closed', count: 0 };
    s.count++;
    s.lastFailure = Date.now();
    if (s.count >= this.threshold) s.status = 'open';
    this.states.set(service, s);
  }

  recordSuccess(service) {
    this.states.set(service, { status: 'closed', count: 0 });
  }
}