分佈式一致性算法--raft
raft算法動畫演示：http://thesecretlivesofdata.com/raft/
1> 3 states
The Follower state
the Candidate state
the Leader state
2> two timeout settings
1.election timeout
The election timeout is the amount of time a follower waits until becoming a candidate.
The election timeout is randomized to be between 150ms and 300ms.
2.heartbeat timeout
3> two step
1.Leader Election
