zookeeper

http://www.ibm.com/developerworks/cn/opensource/os-cn-zookeeper/

http://shiyanjun.cn/archives/474.html

http://wsztrush.github.io/%E7%BC%96%E7%A8%8B%E6%8A%80%E6%9C%AF/2015/12/22/ZOOKEEPER-BASIC.html

过半可用