cluster.go
func DefaultCluster() *Cluster {
	return &Cluster{
		hosts:  make([]*URI, 0),
		okList: make([]bool, 0),
		mutex:  &sync.RWMutex{},
	}
}
func DefaultCluster() *Cluster {
	return &Cluster{
		hosts:  make([]*URI, 0),
		okList: make([]bool, 0),
		mutex:  &sync.RWMutex{},
	}
}
// DefaultCluster returns the default Cluster.