|
n we get a
// quorum. If it is not, the term comes from the node that
// rejected our vote so we should become a follower at the new
// term.
default:
if m.Type == pb.MsgApp || m.Type == pb.MsgHeartbeat || m.Type == pb.MsgSnap {
r.becomeFollower(m.Term, m.From)
} else {
r.becomeFollower(m.Term, None)
}
}
case m.Term < r.Term:
// ........
}
switch m.Type {
case pb.MsgHup:
// ........
case pb.MsgVote, pb.MsgPreVote:
// We can vote if this is a repeat of a vote we've already cast...
canVote := r.Vote == m.From ||
// ...we haven't voted and we don't think there's a leader yet in this term...
(r.Vote == None && r.lead == None) ||
// ...or this is a PreVote for a future term...
(m.Type == pb.MsgPreVote && m.Term > r.Term)
// ...and we believe the candidate is up to date.
if canVote && r.raftLog.isUpToDate(m.Index, m.LogTerm) {
// Note: it turns out that that learners must be allowed to cast votes.
// This seems counter- intuitive but is necessary in the situation in which
// a learner has been promoted (i.e. is now a voter) but has not learned
// about this yet.
// For example, consider a group in which id=1 is a learner and id=2 and
// id=3 are voters. A configuration change promoting 1 can be committed on
// the quorum `{2,3}` without the config change being appended to the
// learner's log. If the leader (say 2) fails, there are de facto two
// voters remaining. Only 3 can win an election (due to its log containing
// all committed entries), but to do so it will need 1 to vote. But 1
// considers itself a learner and will continue to do so until 3 has
// stepped up as leader, replicates the conf change to 1, and 1 applies it.
// Ultimately, by receiving a request to vote, the learner realizes that
// the candidate believes it to be a voter, and that it should act
// accordingly. The candidate's config may be stale, too; but in that case
// it won't win the election, at least in the absence of the bug discussed
// in:
// https://github.com/etcd-io/etcd/issues/7625#issuecomment-488798263.
// When responding to Msg{Pre,}Vote messages we include the term
// from the message, not the local term. To see why, consider the
// case where a single node was previously partitioned away and
// it's local term is now out of date. If we include the local term
// (recall that for pre-votes we don't update the local term), the
// (pre-)campaigning node on the other end will proceed to ignore
// the message (it ignores all out of date messages).
// The term in the original message and current local term are the
// same in the case of regular votes, but different for pre-votes.
r.send(pb.Message{To: m.From, Term: m.Term, Type: voteRespMsgType(m.Type)})
if m.Type == pb.MsgVote {
// Only record real votes.
r.electionElapsed = 0
r.Vote = m.From
}
} else {
r.send(pb.Message{To: m.From, Term: r.Term, Type: voteRespMsgType(m.Type), Reject: true})
}
default:
// ...........
}
return nil
}
注意：节点同意投票消息带的是m.Term，拒绝投票消息是r.Term，如果拒接MsgPreVote消息，那么发送pre-vote消息的节点就变为
在r.Term的follower，在2.3.1节内体现
2.3 节点收到处理MsgPreVoteResp或MsgVoteResp消息流程
2.3.1 Step内处理
根据2.2节可以看到Step内有这样一段代码：在2.2节最后有解释，官方也给了详细注释
switch {
case m.Type == pb.MsgPreVote:
// Never change our term in response to a PreVote
case m.Type == pb.MsgPreVoteResp && !m.Reject:
|