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raft: prevent learners from becoming leader

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We were already taking some precautions against learners campaigning,
but there was no safeguard against an explicit call to `Campaign()`.
The newly added test also verifies that leadership transfers to
learners are ignored.
This commit is contained in:
Tobias Schottdorf 2019-06-17 09:20:45 +02:00
parent 2c5162af5c
commit c844526002
2 changed files with 45 additions and 0 deletions
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11
raft/raft.go
View File

@ -724,7 +724,14 @@ func (r *raft) becomeLeader() {
r.logger.Infof("%x became leader at term %d", r.id, r.Term)
}
// campaign transitions the raft instance to candidate state. This must only be
// called after verifying that this is a legitimate transition.
func (r *raft) campaign(t CampaignType) {
if !r.promotable() {
// This path should not be hit (callers are supposed to check), but
// better safe than sorry.
r.logger.Warningf("%x is unpromotable; campaign() should have been called", r.id)
}
var term uint64
var voteMsg pb.MessageType
if t == campaignPreElection {
@ -858,6 +865,10 @@ func (r *raft) Step(m pb.Message) error {
switch m.Type {
case pb.MsgHup:
if r.state != StateLeader {
if !r.promotable() {
r.logger.Warningf("%x is unpromotable and can not campaign; ignoring MsgHup", r.id)
return nil
}
ents, err := r.raftLog.slice(r.raftLog.applied+1, r.raftLog.committed+1, noLimit)
if err != nil {
r.logger.Panicf("unexpected error getting unapplied entries (%v)", err)

34
raft/raft_test.go
View File

@ -4082,6 +4082,40 @@ func TestPreVoteWithCheckQuorum(t *testing.T) {
}
}
// TestLearnerCampaign verifies that a learner won't campaign even if it receives
// a MsgHup or MsgTimeoutNow.
func TestLearnerCampaign(t *testing.T) {
n1 := newTestRaft(1, []uint64{1}, 10, 1, NewMemoryStorage())
n1.addLearner(2)
n2 := newTestRaft(2, []uint64{1}, 10, 1, NewMemoryStorage())
n2.addLearner(2)
nt := newNetwork(n1, n2)
nt.send(pb.Message{From: 2, To: 2, Type: pb.MsgHup})
if !n2.isLearner {
t.Fatalf("failed to make n2 a learner")
}
if n2.state != StateFollower {
t.Fatalf("n2 campaigned despite being learner")
}
nt.send(pb.Message{From: 1, To: 1, Type: pb.MsgHup})
if n1.state != StateLeader || n1.lead != 1 {
t.Fatalf("n1 did not become leader")
}
// NB: TransferLeader already checks that the recipient is not a learner, but
// the check could have happened by the time the recipient becomes a learner,
// in which case it will receive MsgTimeoutNow as in this test case and we
// verify that it's ignored.
nt.send(pb.Message{From: 1, To: 2, Type: pb.MsgTimeoutNow})
if n2.state != StateFollower {
t.Fatalf("n2 accepted leadership transfer despite being learner")
}
}
// simulate rolling update a cluster for Pre-Vote. cluster has 3 nodes [n1, n2, n3].
// n1 is leader with term 2
// n2 is follower with term 2