节点启动与leader选主分析
节点启动过程
node init的过程：
new NodeMetrics
创建 timerManager
创建需要的定时器:
voteTimer
electionTimer
这两个 timer 的倒计时时间都是根据配置的 (ElectionTimeoutMs, ElectionTimeoutMs + maxElectionDelayMs) 之间进行随机出一个整数作为其倒计时时间。
这两个timer看起来差不多，一个是voteTimer，一个是electionTimer。为啥？ 成为候选人之后再投票？ 没成为候选人时先触发选举？应该是对的， 看对应的回调handleVoteTimeout和handleElectionTimeout的处理，一个是检查STATE_FOLLOWER，另一个是STATE_CANDIDATE。 所以按此角色的判定，要electionTimer的回调逻辑先执行到才行。stepDownTimer
snapshotTimer
创建 applyDisruptor 和 applyQueue
创建 FSMCallerImpl
initLogStorage
initMetaStorage
initFSMCaller
创建BallotBox 并初始化
initSnapshotStorage
logManager.checkConsistency
创建ReplicatorGroupImpl 并在稍后初始化
创建DefaultRaftClientService
创建ReadOnlyServiceImpl并初始化
节点状态初始化为STATE_FOLLOWER 这个对应leader选举 章节中讲到的节点状态机的初始状态
如果这个group只有自己一个节点，那么触发选举自己
节点角色状态机
在理解投票与选举逻辑之前，先要搞清楚节点的状态变化的状态机，这个内容在论文的5.1章节有图讲到。
stateDiagram-v2
[*] --> Follower:starts up
Follower --> Candidate: time out, starts election
Candidate --> Leader: receives votes from majority of servers
Candidate --> Candidate: times out, new election
Leader --> Follower: discovers server with higher term
Candidate --> Follower: discovers current leader or new term最简的理想的变换过程是：
Follower – Candidate – Leader
leader选举过程的简易图示
授权成功的解释
授权成功分为两部分逻辑：
- 远端(即接收到请求的服务端)授权成功
- 本端(即发起请求的客户端)授权成功
远端授权成功逻辑
分析远端授权其实就是分析服务端对预投票和投票的处理逻辑。
handlePreVoteRequest
主要逻辑有：
- 一些合法性校验，比如请求发起端是否在配置的 peer 列表中。
- 请求中的term是否已经小于当前的term，如果是的，那么此次请求授权失败，直接返回响应给发起方。
- checkReplicator
- 比较requestLastLogId和此时再次获取到的lastLogId，如果大于等于，则授权成功，返回响应给发起方。
handleRequestVoteRequest
服务端处理投票和预投票的逻辑还是有些不同的，服务端处理投票的主要逻辑有：
- 一些合法性校验，比如请求发起端是否在配置的 peer 列表中。
- 如果请求的term小于当前term，则此次请求授权失败，并将当前term返回给发起方。
- 如果请求的term大于当前term，则要进入stepDown逻辑(TODO)，后续逻辑继续执行。
- 拿request中的lastLogId和当前获取到的lastLogId比较，如果是大于等于的则算是logIsOK
- 这个时候如果logIsOk，term也是合法(请求term大于等于当前term),且votedId是空的，则处理stepDown逻辑(TODO)且将发起请求的serverid作为votedId，并用metaStorage存储为这个candidateId在投票。
- 最后返回是否授权成功，此处，是否授权成功，还是再判断一次的，判断规则是：request.getTerm() == this.currTerm && candidateId.equals(this.votedId)
本端授权成功逻辑
分析本端授权主要是分析Ballot的授权逻辑。分析Ballot授权逻辑之前要分析其init逻辑。
Ballot init分析
Ballot的grant之前都会init， 且这两个同时出现执行，出现在preVote和electSelf中，preVote对应的是prevVoteCtx(Ballot的实例)，electSelf对应的是voteCtx(Ballot的实例)。
init逻辑
- init时将迭代conf中所有的peer构建为UnfoundPeerId，并用index按序标志。并将UnfoundPeerId实例添加到Ballot的peers字段中。
- Ballot的quorum字段初始化为peer个数的一半加1。
- 如果有oldConf则按上述逻辑同样处理，不过相应的结果都是维护在oldXX字段中。
Ballot grant分析
grant逻辑：
如果直接对某个peer grant，则用new 的PosHint，PosHint初始的pos0、pos1都是-1 , -1则意味着按serverid比对迭代查找(逻辑没啥区别，只是不是直接取到)。
如果这个peer没有被found，那么quorm减1。这个peer包括发起预投票或者投票时的发起方自己，也包括应答了这个请求并且授权成功的对端。这个逻辑非常重要。
详细的过程可以参见下面相关日志做了注释的部分：// node1的日志，这个节点接下来会被选为leader 2021-10-23 22:46:59 [JRaft-ElectionTimer-<election_test/127.0.0.1:8081>0] INFO NodeImpl:2669 - preVote before grant, serverId 127.0.0.1:8081 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=false, index=2]], quorum=2, oldPeers=[], oldQuorum=0] 2021-10-23 22:46:59 [JRaft-ElectionTimer-<election_test/127.0.0.1:8081>0] INFO NodeImpl:2670 - preVote after grant, serverId 127.0.0.1:8081 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=true, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=false, index=2]], quorum=1, oldPeers=[], oldQuorum=0] // 此时quorum 变成1 Ballot grant的是他自己： serverId 127.0.0.1:8081 2021-10-23 22:46:59 [JRaft-RPC-Processor-0] INFO NodeImpl:2577 - Node <election_test/127.0.0.1:8081> received PreVoteResponse from 127.0.0.1:8082, term=0, granted=true. 2021-10-23 22:46:59 [JRaft-RPC-Processor-0] INFO NodeImpl:2580 - handlePreVoteResponse before grant, peerId 127.0.0.1:8082 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=true, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=false, index=2]], quorum=1, oldPeers=[], oldQuorum=0] 2021-10-23 22:46:59 [JRaft-RPC-Processor-0] INFO NodeImpl:2581 - handlePreVoteResponse after grant, peerId 127.0.0.1:8082 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=true, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=true, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=false, index=2]], quorum=0, oldPeers=[], oldQuorum=0] // 此时quorum 变成0 那么表示pre vote成功 Ballot grant的是他发送的对端： peerId 127.0.0.1:8082 //............ 2021-10-23 22:46:59 [JRaft-RPC-Processor-1] INFO Replicator:897 - Replicator=Replicator [state=Created, statInfo=<running=null, firstLogIndex=0, lastLogIncluded=0, lastLogIndex=0, lastTermIncluded=0>, peerId=127.0.0.1:8082, type=Follower]@127.0.0.1:8082 is started //成为leader之后就是一直发空的AppendEntriesRequest请求了 此时per_log_term和pre_log_index都是0 2021-10-23 22:46:59 [JRaft-RPC-Processor-1] INFO AbstractClientService:195 - ===invokeWithDone, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8081" peer_id: "127.0.0.1:8082" term: 1 prev_log_term: 0 prev_log_index: 0 committed_index: 0 data: "" //............ 2021-10-23 22:46:59 [JRaft-FSMCaller-Disruptor-0] INFO StateMachineAdapter:62 - onLeaderStart: term=1. [ElectionBootstrap] Leader's ip is: 127.0.0.1, port: 8081 [ElectionBootstrap] Leader start on term: 1 2021-10-23 22:46:59 [JRaft-Rpc-Closure-Executor-1] INFO AbstractClientService:195 - ===invokeWithDone, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8081" peer_id: "127.0.0.1:8082" term: 1 prev_log_term: 1 prev_log_index: 1 committed_index: 1 //............ 2021-10-23 22:47:55 [election_test/PeerPair[127.0.0.1:8081 -> 127.0.0.1:8083]-AppendEntriesThread0] INFO NodeImpl:1878 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8081" term: 2 prev_log_term: 2 prev_log_index: 2 committed_index: 2 data: "" // ............ 2021-10-23 22:47:56 [election_test/PeerPair[127.0.0.1:8081 -> 127.0.0.1:8083]-AppendEntriesThread0] INFO NodeImpl:1878 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8081" term: 2 prev_log_term: 1 prev_log_index: 1 entries { term: 2 type: ENTRY_TYPE_CONFIGURATION peers: "127.0.0.1:8081" peers: "127.0.0.1:8082" peers: "127.0.0.1:8083" data_len: 0 } committed_index: 2 // node2的日志，他响应了node1的预投票和投票请求 2021-10-23 22:46:58 [main] INFO RaftGroupService:136 - Start the RaftGroupService successfully. 2021-10-23 22:46:59 [Bolt-default-executor-6-thread-2] INFO NodeImpl:1635 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8081" peer_id: "127.0.0.1:8082" term: 1 last_log_term: 0 last_log_index: 0 pre_vote: true // 预投票的日志 2021-10-23 22:46:59 [Bolt-default-executor-6-thread-2] INFO NodeImpl:1689 - Node <election_test/127.0.0.1:8082> received PreVoteRequest from 127.0.0.1:8081, term=1, currTerm=0, granted=true, requestLastLogId=LogId [index=0, term=0], lastLogId=LogId [index=0, term=0]. 2021-10-23 22:46:59 [Bolt-default-executor-6-thread-3] INFO NodeImpl:1736 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8081" peer_id: "127.0.0.1:8082" term: 1 last_log_term: 0 last_log_index: 0 pre_vote: false // 投票的日志 2021-10-23 22:46:59 [Bolt-default-executor-6-thread-3] INFO NodeImpl:1760 - Node <election_test/127.0.0.1:8082> received RequestVoteRequest from 127.0.0.1:8081, term=1, currTerm=0. 2021-10-23 22:46:59 [Bolt-default-executor-6-thread-3] INFO LocalRaftMetaStorage:132 - Save raft meta, path=/tmp/server2/meta, term=1, votedFor=0.0.0.0:0, cost time=155 ms 2021-10-23 22:46:59 [Bolt-default-executor-6-thread-3] INFO LocalRaftMetaStorage:132 - Save raft meta, path=/tmp/server2/meta, term=1, votedFor=127.0.0.1:8081, cost time=77 ms //............ 2021-10-23 22:46:59 [election_test/PeerPair[127.0.0.1:8082 -> 127.0.0.1:8081]-AppendEntriesThread0] INFO NodeImpl:1878 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8081" peer_id: "127.0.0.1:8082" term: 1 prev_log_term: 0 prev_log_index: 0 committed_index: 0 data: "" //............ 2021-10-23 22:46:59 [election_test/PeerPair[127.0.0.1:8082 -> 127.0.0.1:8081]-AppendEntriesThread0] INFO NodeImpl:1878 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8081" peer_id: "127.0.0.1:8082" term: 1 prev_log_term: 1 prev_log_index: 1 committed_index: 1 //............ 2021-10-23 22:47:35 [Bolt-conn-event-executor-10-thread-1] INFO RpcRequestProcessor:279 - Destroyed peer request context for election_test/PeerPair[127.0.0.1:8082 -> 127.0.0.1:8081] 2021-10-23 22:47:37 [Bolt-default-executor-6-thread-5] INFO NodeImpl:1635 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 last_log_term: 1 last_log_index: 1 pre_vote: true 2021-10-23 22:47:37 [Bolt-default-executor-6-thread-5] INFO NodeImpl:1689 - Node <election_test/127.0.0.1:8082> received PreVoteRequest from 127.0.0.1:8083, term=2, currTerm=1, granted=true, requestLastLogId=LogId [index=1, term=1], lastLogId=LogId [index=1, term=1]. 2021-10-23 22:47:37 [Bolt-default-executor-6-thread-6] INFO NodeImpl:1736 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 last_log_term: 1 last_log_index: 1 pre_vote: false 2021-10-23 22:47:37 [Bolt-default-executor-6-thread-6] INFO NodeImpl:1760 - Node <election_test/127.0.0.1:8082> received RequestVoteRequest from 127.0.0.1:8083, term=2, currTerm=1. 2021-10-23 22:47:37 [JRaft-FSMCaller-Disruptor-0] INFO StateMachineAdapter:84 - onStopFollowing: LeaderChangeContext [leaderId=127.0.0.1:8081, term=1, status=Status[EHIGHERTERMRESPONSE<10008>: Raft node receives higher term RequestVoteRequest.]]. 2021-10-23 22:47:37 [Bolt-default-executor-6-thread-6] INFO LocalRaftMetaStorage:132 - Save raft meta, path=/tmp/server2/meta, term=2, votedFor=0.0.0.0:0, cost time=71 ms 2021-10-23 22:47:37 [Bolt-default-executor-6-thread-6] INFO LocalRaftMetaStorage:132 - Save raft meta, path=/tmp/server2/meta, term=2, votedFor=127.0.0.1:8083, cost time=71 ms 2021-10-23 22:47:37 [election_test/PeerPair[127.0.0.1:8082 -> 127.0.0.1:8083]-AppendEntriesThread0] INFO NodeImpl:1878 - ===handle rpc request, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 prev_log_term: 1 prev_log_index: 1 committed_index: 1 data: "" // node3 日志，主要体现当时做了一次leader切换的过程(此时停了node1了，node3上来接管了) 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO AbstractClientService:195 - ===invokeWithDone, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 last_log_term: 1 last_log_index: 1 pre_vote: true 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO BoltRpcClient:102 - ==== invokeSync 127.0.0.1:8081, class com.alipay.sofa.jraft.rpc.RpcRequests$PingRequest ============= 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO NodeImpl:2669 - preVote before grant, serverId 127.0.0.1:8083 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=false, index=2]], quorum=2, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO NodeImpl:2670 - preVote after grant, serverId 127.0.0.1:8083 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=true, index=2]], quorum=1, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO NodeImpl:2577 - Node <election_test/127.0.0.1:8083> received PreVoteResponse from 127.0.0.1:8082, term=1, granted=true. ============= 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO NodeImpl:2580 - handlePreVoteResponse before grant, peerId 127.0.0.1:8082 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=true, index=2]], quorum=1, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO NodeImpl:2581 - handlePreVoteResponse after grant, peerId 127.0.0.1:8082 ,,, prevVoteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=true, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=true, index=2]], quorum=0, oldPeers=[], oldQuorum=0] ============= 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO NodeImpl:1120 - Node <election_test/127.0.0.1:8083> start vote and grant vote self, term=1. 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO AbstractClientService:195 - ===invokeWithDone, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 last_log_term: 1 last_log_index: 1 pre_vote: false 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO LocalRaftMetaStorage:132 - Save raft meta, path=/tmp/server3/meta, term=2, votedFor=127.0.0.1:8083, cost time=95 ms 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO NodeImpl:1172 - electSelf before grant, serverId 127.0.0.1:8083 ,,, voteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=false, index=2]], quorum=2, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-RPC-Processor-0] INFO NodeImpl:1173 - electSelf after grant, serverId 127.0.0.1:8083 ,,, voteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=true, index=2]], quorum=1, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-RPC-Processor-1] INFO NodeImpl:2518 - handleRequestVoteResponse before grant, peerId 127.0.0.1:8082 ,,, voteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=false, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=true, index=2]], quorum=1, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-RPC-Processor-1] INFO NodeImpl:2519 - handleRequestVoteResponse after grant, peerId 127.0.0.1:8082 ,,, voteCtx Ballot [peers=[UnfoundPeerId [peerId=127.0.0.1:8081, found=false, index=0], UnfoundPeerId [peerId=127.0.0.1:8082, found=true, index=1], UnfoundPeerId [peerId=127.0.0.1:8083, found=true, index=2]], quorum=0, oldPeers=[], oldQuorum=0] 2021-10-23 22:47:37 [JRaft-RPC-Processor-1] INFO NodeImpl:1217 - Node <election_test/127.0.0.1:8083> become leader of group, term=2, conf=127.0.0.1:8081,127.0.0.1:8082,127.0.0.1:8083, oldConf=.// node3变成leader 2021-10-23 22:47:37 [JRaft-RPC-Processor-1] INFO Replicator:897 - Replicator=Replicator [state=Created, statInfo=<running=null, firstLogIndex=0, lastLogIncluded=0, lastLogIndex=0, lastTermIncluded=0>, peerId=127.0.0.1:8082, type=Follower]@127.0.0.1:8082 is started 2021-10-23 22:47:37 [JRaft-RPC-Processor-1] INFO AbstractClientService:195 - ===invokeWithDone, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$AppendEntriesRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 prev_log_term: 1 prev_log_index: 1 committed_index: 1 data: "" // ............ 2021-10-23 22:47:35 [Bolt-conn-event-executor-10-thread-1] INFO RpcRequestProcessor:279 - Destroyed peer request context for election_test/PeerPair[127.0.0.1:8083 -> 127.0.0.1:8081] 2021-10-23 22:47:37 [JRaft-FSMCaller-Disruptor-0] INFO StateMachineAdapter:84 - onStopFollowing: LeaderChangeContext [leaderId=127.0.0.1:8081, term=1, status=Status[ERAFTTIMEDOUT<10001>: Lost connection from leader 127.0.0.1:8081.]]. 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO NodeImpl:2623 - Node <election_test/127.0.0.1:8083> term 1 start preVote. 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO BoltRpcClient:102 - ==== invokeSync 127.0.0.1:8082, class com.alipay.sofa.jraft.rpc.RpcRequests$PingRequest 2021-10-23 22:47:37 [Bolt-conn-event-executor-5-thread-1] INFO ClientServiceConnectionEventProcessor:50 - Peer 127.0.0.1:8082 is connected 2021-10-23 22:47:37 [JRaft-ElectionTimer-<election_test/127.0.0.1:8083>0] INFO AbstractClientService:195 - ===invokeWithDone, request is : class com.alipay.sofa.jraft.rpc.RpcRequests$RequestVoteRequest group_id: "election_test" server_id: "127.0.0.1:8083" peer_id: "127.0.0.1:8082" term: 2 last_log_term: 1 last_log_index: 1 pre_vote: true如上有两条重要的地方，如日志中的注释：
此时quorum 变成1 Ballot grant的是他自己： serverId 127.0.0.1:8081
此时quorum 变成0 那么表示pre vote成功 Ballot grant的是他发送的对端： peerId 127.0.0.1:8082
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