Designing a High-Throughput API Rate Limiter for Microservices

class TokenBucket {
  constructor(capacity, refillRate) {
    this.capacity = capacity;
    this.refillRate = refillRate;
    this.tokens = capacity;
    this.lastRefill = Date.now();
  }

  allowRequest() {
    const now = Date.now();
    const elapsed = (now - this.lastRefill) / 1000;
    this.tokens = Math.min(this.capacity, this.tokens + elapsed * this.refillRate);
    this.lastRefill = now;

    if (this.tokens >= 1) {
      this.tokens -= 1;
      return true;
    }
    return false;
  }
}

const bucket = new TokenBucket(3, 1);
console.log("Allowed:", bucket.allowRequest());