参考：
https://segmentfault.com/a/1190000011265918
美团分布式会话跟踪系统架构设计与实践 https://zhuanlan.zhihu.com/p/23038157
https://www.cnblogs.com/davidwang456/articles/9008893.html
https://www.oschina.net/translate/distributed-tracing-design-architecture