参见：http://dubbo.apache.org/zh-cn/blog/dubbo-loadbalance.html dubbo的负载均衡
https://www.cnblogs.com/cdfive2018/p/10204720.html dubbo的超时重试机制
https://www.jianshu.com/p/4802a512d2c2 dubbo的集群容错机制
https://www.cnblogs.com/xhj123/p/9087532.html dubbo的超时重试与集群容错机制