code: func (pool *LoadBalancedPool) markInstanceDown(
  	idx int, instance *instancePool, downUntil int64) {
  	pool.lock.Lock()
  	defer pool.lock.Unlock()
  	if idx < len(pool.instanceList) && pool.instanceList[idx] == instance {
  		pool.markDownUntil[idx] = downUntil
  	}
  }
docs: // Marks instance down till downUntil epoch in seconds.