From 4e0b605c99ecb325575042a00103e64e88db897f Mon Sep 17 00:00:00 2001 From: Aaron Lehmann Date: Wed, 8 Feb 2017 15:22:09 -0800 Subject: [PATCH] raft: Use TransferLeadership to make leader demotion safer When we demote the leader, we currently wait for all queued messages to be sent, as a best-effort approach to making sure the other nodes find out that the node removal has been committed, and stop treating the current leader as a cluster member. This doesn't work perfectly. To make this more robust, use TransferLeadership when the leader is trying to remove itself, then call the Leave RPC on the new leader once the transfer has completed. Signed-off-by: Aaron Lehmann --- manager/state/raft/raft.go | 81 ++++++++++++++++++++--- manager/state/raft/transport/transport.go | 13 ++++ 2 files changed, 84 insertions(+), 10 deletions(-) diff --git a/manager/state/raft/raft.go b/manager/state/raft/raft.go index ba77ae0ef6..6187e11938 100644 --- a/manager/state/raft/raft.go +++ b/manager/state/raft/raft.go @@ -412,7 +412,7 @@ func (n *Node) JoinAndStart(ctx context.Context) (err error) { defer conn.Close() client := api.NewRaftMembershipClient(conn) - joinCtx, joinCancel := context.WithTimeout(ctx, 10*time.Second) + joinCtx, joinCancel := context.WithTimeout(ctx, n.reqTimeout()) defer joinCancel() resp, err := client.Join(joinCtx, &api.JoinRequest{ Addr: n.opts.Addr, @@ -1030,6 +1030,10 @@ func (n *Node) UpdateNode(id uint64, addr string) { // from a member who is willing to leave its raft // membership to an active member of the raft func (n *Node) Leave(ctx context.Context, req *api.LeaveRequest) (*api.LeaveResponse, error) { + if req.Node == nil { + return nil, grpc.Errorf(codes.InvalidArgument, "no node information provided") + } + nodeInfo, err := ca.RemoteNode(ctx) if err != nil { return nil, err @@ -1100,18 +1104,72 @@ func (n *Node) removeMember(ctx context.Context, id uint64) error { n.membershipLock.Lock() defer n.membershipLock.Unlock() - if n.CanRemoveMember(id) { - cc := raftpb.ConfChange{ - ID: id, - Type: raftpb.ConfChangeRemoveNode, - NodeID: id, - Context: []byte(""), + if !n.CanRemoveMember(id) { + return ErrCannotRemoveMember + } + + if id == n.Config.ID { + // To avoid a corner case with self-removal, transfer leadership + // to another node and ask that node to remove us. + if err := n.removeSelfGracefully(ctx); err != nil { + log.G(ctx).WithError(err).Error("failed to leave raft cluster gracefully") + } else { + return nil } - err := n.configure(ctx, cc) + } + + cc := raftpb.ConfChange{ + ID: id, + Type: raftpb.ConfChangeRemoveNode, + NodeID: id, + Context: []byte(""), + } + return n.configure(ctx, cc) +} + +// removeSelfGracefully initiates a leadership transfer and calls Leave on the +// new leader. It must be called with stopMu held. +func (n *Node) removeSelfGracefully(ctx context.Context) error { + transferCtx, cancelTransfer := context.WithTimeout(ctx, n.reqTimeout()) + defer cancelTransfer() + + if err := n.transferLeadership(transferCtx); err != nil { + return errors.Wrap(err, "failed to transfer leadership") + } + conn, err := n.transport.PeerConn(n.leader()) + if err != nil { return err } + _, err = api.NewRaftMembershipClient(conn).Leave(ctx, &api.LeaveRequest{Node: &api.RaftMember{RaftID: n.Config.ID}}) + return err +} - return ErrCannotRemoveMember +// transferLeadership attempts to transfer leadership to a different node, +// and wait for the transfer to happen. It must be called with stopMu held. +func (n *Node) transferLeadership(ctx context.Context) error { + transferee, err := n.transport.LongestActive() + if err != nil { + return errors.Wrap(err, "failed to get longest-active member") + } + start := time.Now() + log.G(ctx).Infof("raft: transfer leadership %x -> %x", n.Config.ID, transferee) + n.raftNode.TransferLeadership(ctx, n.Config.ID, transferee) + ticker := time.NewTicker(n.opts.TickInterval / 10) + defer ticker.Stop() + var leader uint64 + for { + leader = n.leader() + if leader != raft.None && leader != n.Config.ID { + break + } + select { + case <-ctx.Done(): + return ctx.Err() + case <-ticker.C: + } + } + log.G(ctx).Infof("raft: transfer leadership %x -> %x finished in %v", n.Config.ID, leader, time.Since(start)) + return nil } // RemoveMember submits a configuration change to remove a member from the raft cluster @@ -1738,7 +1796,6 @@ func (n *Node) applyRemoveNode(ctx context.Context, cc raftpb.ConfChange) (err e // while n.asyncTasks.Wait() could be helpful in this case // it's the best-effort strategy, because this send could be fail due to some errors (such as time limit exceeds) - // TODO(Runshen Zhu): use leadership transfer to solve this case, after vendoring raft 3.0+ } else { if err := n.transport.RemovePeer(cc.NodeID); err != nil { return err @@ -1852,3 +1909,7 @@ func getIDs(snap *raftpb.Snapshot, ents []raftpb.Entry) []uint64 { } return sids } + +func (n *Node) reqTimeout() time.Duration { + return 5*time.Second + 2*time.Duration(n.Config.ElectionTick)*n.opts.TickInterval +} diff --git a/manager/state/raft/transport/transport.go b/manager/state/raft/transport/transport.go index ec1e971cf3..9ce8efd51b 100644 --- a/manager/state/raft/transport/transport.go +++ b/manager/state/raft/transport/transport.go @@ -295,6 +295,19 @@ func (t *Transport) Active(id uint64) bool { return active } +// LongestActive returns the ID of the peer that has been active for the longest +// length of time. +func (t *Transport) LongestActive() (uint64, error) { + p, err := t.longestActive() + if err != nil { + return 0, err + } + + return p.id, nil +} + +// longestActive returns the peer that has been active for the longest length of +// time. func (t *Transport) longestActive() (*peer, error) { var longest *peer var longestTime time.Time