raft: Introduce MultiNode.

MultiNode is an alternative to raft.Node that is more efficient when a node may participate in many consensus groups. It is currently used in the CockroachDB project; this commit merges the github.com/cockroachdb/etcd fork back into the mainline.
2024-09-27 06:25:44 +00:00 · 2015-03-04 15:30:21 -05:00 · 2015-03-04 15:30:21 -05:00 · 4e74d81bbb
commit 4e74d81bbb
parent 559466e996
2 changed files with 843 additions and 0 deletions
--- a/raft/multinode.go
+++ b/raft/multinode.go
@ -0,0 +1,449 @@
+package raft
+
+import (
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	pb "github.com/coreos/etcd/raft/raftpb"
+)
+
+// MultiNode represents a node that is participating in multiple consensus groups.
+// A MultiNode is more efficient than a collection of Nodes.
+// The methods of this interface correspond to the methods of Node and are described
+// more fully there.
+type MultiNode interface {
+	// CreateGroup adds a new group to the MultiNode. The application must call CreateGroup
+	// on each particpating node with the same group ID; it may create groups on demand as it
+	// receives messages. If the given storage contains existing log entries the list of peers
+	// may be empty.
+	CreateGroup(group uint64, peers []Peer, storage Storage) error
+	// RemoveGroup removes a group from the MultiNode.
+	RemoveGroup(group uint64) error
+	// Tick advances the internal logical clock by a single tick.
+	Tick()
+	// Campaign causes this MultiNode to transition to candidate state in the given group.
+	Campaign(ctx context.Context, group uint64) error
+	// Propose proposes that data be appended to the given group's log.
+	Propose(ctx context.Context, group uint64, data []byte) error
+	// ProposeConfChange proposes a config change.
+	ProposeConfChange(ctx context.Context, group uint64, cc pb.ConfChange) error
+	// ApplyConfChange applies a config change to the local node.
+	ApplyConfChange(group uint64, cc pb.ConfChange) *pb.ConfState
+	// Step advances the state machine using the given message.
+	Step(ctx context.Context, group uint64, msg pb.Message) error
+	// Ready returns a channel that returns the current point-in-time state of any ready
+	// groups. Only groups with something to report will appear in the map.
+	Ready() <-chan map[uint64]Ready
+	// Advance notifies the node that the application has applied and saved progress in the
+	// last Ready results. It must be called with the last value returned from the Ready()
+	// channel.
+	Advance(map[uint64]Ready)
+	// Status returns the current status of the given group.
+	Status(group uint64) Status
+	// Stop performs any necessary termination of the MultiNode.
+	Stop()
+}
+
+// StartMultiNode creates a MultiNode and starts its background goroutine.
+// The id identifies this node and will be used as its node ID in all groups.
+// The election and heartbeat timers are in units of ticks.
+func StartMultiNode(id uint64, election, heartbeat int) MultiNode {
+	mn := newMultiNode(id, election, heartbeat)
+	go mn.run()
+	return &mn
+}
+
+// TODO(bdarnell): add group ID to the underlying protos?
+type multiMessage struct {
+	group uint64
+	msg   pb.Message
+}
+
+type multiConfChange struct {
+	group uint64
+	msg   pb.ConfChange
+	ch    chan pb.ConfState
+}
+
+type multiStatus struct {
+	group uint64
+	ch    chan Status
+}
+
+type groupCreation struct {
+	id      uint64
+	peers   []Peer
+	storage Storage
+	// TODO(bdarnell): do we really need the done channel here? It's
+	// unlike the rest of this package, but we need the group creation
+	// to be complete before any Propose or other calls.
+	done chan struct{}
+}
+
+type groupRemoval struct {
+	id uint64
+	// TODO(bdarnell): see comment on groupCreation.done
+	done chan struct{}
+}
+
+type multiNode struct {
+	id        uint64
+	election  int
+	heartbeat int
+	groupc    chan groupCreation
+	rmgroupc  chan groupRemoval
+	propc     chan multiMessage
+	recvc     chan multiMessage
+	confc     chan multiConfChange
+	readyc    chan map[uint64]Ready
+	advancec  chan map[uint64]Ready
+	tickc     chan struct{}
+	stop      chan struct{}
+	done      chan struct{}
+	status    chan multiStatus
+}
+
+func newMultiNode(id uint64, election, heartbeat int) multiNode {
+	return multiNode{
+		id:        id,
+		election:  election,
+		heartbeat: heartbeat,
+		groupc:    make(chan groupCreation),
+		rmgroupc:  make(chan groupRemoval),
+		propc:     make(chan multiMessage),
+		recvc:     make(chan multiMessage),
+		confc:     make(chan multiConfChange),
+		readyc:    make(chan map[uint64]Ready),
+		advancec:  make(chan map[uint64]Ready),
+		tickc:     make(chan struct{}),
+		stop:      make(chan struct{}),
+		done:      make(chan struct{}),
+		status:    make(chan multiStatus),
+	}
+}
+
+type groupState struct {
+	id         uint64
+	raft       *raft
+	prevSoftSt *SoftState
+	prevHardSt pb.HardState
+	prevSnapi  uint64
+}
+
+func (g *groupState) newReady() Ready {
+	return newReady(g.raft, g.prevSoftSt, g.prevHardSt)
+}
+
+func (g *groupState) commitReady(rd Ready) {
+	if rd.SoftState != nil {
+		g.prevSoftSt = rd.SoftState
+	}
+	if !IsEmptyHardState(rd.HardState) {
+		g.prevHardSt = rd.HardState
+	}
+	if !IsEmptySnap(rd.Snapshot) {
+		g.prevSnapi = rd.Snapshot.Metadata.Index
+		g.raft.raftLog.stableSnapTo(g.prevSnapi)
+	}
+	if len(rd.Entries) > 0 {
+		// TODO(bdarnell): stableTo(rd.Snapshot.Index) if any
+		e := rd.Entries[len(rd.Entries)-1]
+		g.raft.raftLog.stableTo(e.Index, e.Term)
+	}
+
+	// TODO(bdarnell): in node.go, Advance() ignores CommittedEntries and calls
+	// appliedTo with HardState.Commit, but this causes problems in multinode/cockroach.
+	// The two should be the same except for the special-casing of the initial ConfChange
+	// entries.
+	if len(rd.CommittedEntries) > 0 {
+		g.raft.raftLog.appliedTo(rd.CommittedEntries[len(rd.CommittedEntries)-1].Index)
+	}
+	//g.raft.raftLog.appliedTo(rd.HardState.Commit)
+}
+
+func (mn *multiNode) run() {
+	groups := map[uint64]*groupState{}
+	rds := map[uint64]Ready{}
+	var advancec chan map[uint64]Ready
+	for {
+		// Only select readyc if we have something to report and we are not
+		// currently waiting for an advance.
+		readyc := mn.readyc
+		if len(rds) == 0 || advancec != nil {
+			readyc = nil
+		}
+
+		// group points to the group that was touched on this iteration (if any)
+		var group *groupState
+		select {
+		case gc := <-mn.groupc:
+			// TODO(bdarnell): pass applied through gc and into newRaft. Or get rid of it?
+			r := newRaft(mn.id, nil, mn.election, mn.heartbeat, gc.storage, 0)
+			group = &groupState{
+				id:         gc.id,
+				raft:       r,
+				prevSoftSt: r.softState(),
+				prevHardSt: r.HardState,
+			}
+			groups[gc.id] = group
+			lastIndex, err := gc.storage.LastIndex()
+			if err != nil {
+				panic(err) // TODO(bdarnell)
+			}
+			// If the log is empty, this is a new group (like StartNode); otherwise it's
+			// restoring an existing group (like RestartNode).
+			// TODO(bdarnell): rethink group initialization and whether the application needs
+			// to be able to tell us when it expects the group to exist.
+			if lastIndex == 0 {
+				r.becomeFollower(1, None)
+				ents := make([]pb.Entry, len(gc.peers))
+				for i, peer := range gc.peers {
+					cc := pb.ConfChange{Type: pb.ConfChangeAddNode, NodeID: peer.ID, Context: peer.Context}
+					data, err := cc.Marshal()
+					if err != nil {
+						panic("unexpected marshal error")
+					}
+					ents[i] = pb.Entry{Type: pb.EntryConfChange, Term: 1, Index: uint64(i + 1), Data: data}
+				}
+				r.raftLog.append(ents...)
+				r.raftLog.committed = uint64(len(ents))
+				for _, peer := range gc.peers {
+					r.addNode(peer.ID)
+				}
+			}
+			close(gc.done)
+
+		case gr := <-mn.rmgroupc:
+			delete(groups, gr.id)
+			delete(rds, gr.id)
+			close(gr.done)
+
+		case mm := <-mn.propc:
+			// TODO(bdarnell): single-node impl doesn't read from propc unless the group
+			// has a leader; we can't do that since we have one propc for many groups.
+			// We'll have to buffer somewhere on a group-by-group basis, or just let
+			// raft.Step drop any such proposals on the floor.
+			mm.msg.From = mn.id
+			group = groups[mm.group]
+			group.raft.Step(mm.msg)
+
+		case mm := <-mn.recvc:
+			group = groups[mm.group]
+			if _, ok := group.raft.prs[mm.msg.From]; ok || !IsResponseMsg(mm.msg) {
+				group.raft.Step(mm.msg)
+			}
+
+		case mcc := <-mn.confc:
+			group = groups[mcc.group]
+			if mcc.msg.NodeID == None {
+				group.raft.resetPendingConf()
+				select {
+				case mcc.ch <- pb.ConfState{Nodes: group.raft.nodes()}:
+				case <-mn.done:
+				}
+				break
+			}
+			switch mcc.msg.Type {
+			case pb.ConfChangeAddNode:
+				group.raft.addNode(mcc.msg.NodeID)
+			case pb.ConfChangeRemoveNode:
+				group.raft.removeNode(mcc.msg.NodeID)
+			case pb.ConfChangeUpdateNode:
+				group.raft.resetPendingConf()
+			default:
+				panic("unexpected conf type")
+			}
+			select {
+			case mcc.ch <- pb.ConfState{Nodes: group.raft.nodes()}:
+			case <-mn.done:
+			}
+
+		case <-mn.tickc:
+			// TODO(bdarnell): instead of calling every group on every tick,
+			// we should have a priority queue of groups based on their next
+			// time-based event.
+			for _, g := range groups {
+				g.raft.tick()
+				rd := g.newReady()
+				if rd.containsUpdates() {
+					rds[g.id] = rd
+				}
+			}
+
+		case readyc <- rds:
+			// Clear outgoing messages as soon as we've passed them to the application.
+			for g := range rds {
+				groups[g].raft.msgs = nil
+			}
+			rds = map[uint64]Ready{}
+			advancec = mn.advancec
+
+		case advs := <-advancec:
+			for groupID, rd := range advs {
+				group, ok := groups[groupID]
+				if !ok {
+					continue
+				}
+				group.commitReady(rd)
+
+				// We've been accumulating new entries in rds which may now be obsolete.
+				// Drop the old Ready object and create a new one if needed.
+				delete(rds, groupID)
+				newRd := group.newReady()
+				if newRd.containsUpdates() {
+					rds[groupID] = newRd
+				}
+			}
+			advancec = nil
+
+		case ms := <-mn.status:
+			ms.ch <- getStatus(groups[ms.group].raft)
+
+		case <-mn.stop:
+			close(mn.done)
+			return
+		}
+
+		if group != nil {
+			rd := group.newReady()
+			if rd.containsUpdates() {
+				rds[group.id] = rd
+			}
+		}
+	}
+}
+
+func (mn *multiNode) CreateGroup(id uint64, peers []Peer, storage Storage) error {
+	gc := groupCreation{
+		id:      id,
+		peers:   peers,
+		storage: storage,
+		done:    make(chan struct{}),
+	}
+	mn.groupc <- gc
+	select {
+	case <-gc.done:
+		return nil
+	case <-mn.done:
+		return ErrStopped
+	}
+}
+
+func (mn *multiNode) RemoveGroup(id uint64) error {
+	gr := groupRemoval{
+		id:   id,
+		done: make(chan struct{}),
+	}
+	mn.rmgroupc <- gr
+	select {
+	case <-gr.done:
+		return nil
+	case <-mn.done:
+		return ErrStopped
+	}
+}
+
+func (mn *multiNode) Stop() {
+	select {
+	case mn.stop <- struct{}{}:
+	case <-mn.done:
+	}
+	<-mn.done
+}
+
+func (mn *multiNode) Tick() {
+	select {
+	case mn.tickc <- struct{}{}:
+	case <-mn.done:
+	}
+}
+
+func (mn *multiNode) Campaign(ctx context.Context, group uint64) error {
+	return mn.step(ctx, multiMessage{group,
+		pb.Message{
+			Type: pb.MsgHup,
+		},
+	})
+}
+
+func (mn *multiNode) Propose(ctx context.Context, group uint64, data []byte) error {
+	return mn.step(ctx, multiMessage{group,
+		pb.Message{
+			Type: pb.MsgProp,
+			Entries: []pb.Entry{
+				{Data: data},
+			},
+		}})
+}
+
+func (mn *multiNode) ProposeConfChange(ctx context.Context, group uint64, cc pb.ConfChange) error {
+	data, err := cc.Marshal()
+	if err != nil {
+		return err
+	}
+	return mn.Step(ctx, group,
+		pb.Message{
+			Type: pb.MsgProp,
+			Entries: []pb.Entry{
+				{Type: pb.EntryConfChange, Data: data},
+			},
+		})
+}
+
+func (mn *multiNode) step(ctx context.Context, m multiMessage) error {
+	ch := mn.recvc
+	if m.msg.Type == pb.MsgProp {
+		ch = mn.propc
+	}
+
+	select {
+	case ch <- m:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-mn.done:
+		return ErrStopped
+	}
+}
+
+func (mn *multiNode) ApplyConfChange(group uint64, cc pb.ConfChange) *pb.ConfState {
+	mcc := multiConfChange{group, cc, make(chan pb.ConfState)}
+	select {
+	case mn.confc <- mcc:
+	case <-mn.done:
+	}
+	select {
+	case cs := <-mcc.ch:
+		return &cs
+	case <-mn.done:
+		// Per comments on Node.ApplyConfChange, this method should never return nil.
+		return &pb.ConfState{}
+	}
+}
+
+func (mn *multiNode) Step(ctx context.Context, group uint64, m pb.Message) error {
+	// ignore unexpected local messages receiving over network
+	if IsLocalMsg(m) {
+		// TODO: return an error?
+		return nil
+	}
+	return mn.step(ctx, multiMessage{group, m})
+}
+
+func (mn *multiNode) Ready() <-chan map[uint64]Ready {
+	return mn.readyc
+}
+
+func (mn *multiNode) Advance(rds map[uint64]Ready) {
+	select {
+	case mn.advancec <- rds:
+	case <-mn.done:
+	}
+}
+
+func (mn *multiNode) Status(group uint64) Status {
+	ms := multiStatus{
+		group: group,
+		ch:    make(chan Status),
+	}
+	mn.status <- ms
+	return <-ms.ch
+}
--- a/raft/multinode_test.go
+++ b/raft/multinode_test.go
@ -0,0 +1,394 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package raft
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+	"time"
+
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	"github.com/coreos/etcd/raft/raftpb"
+)
+
+// TestMultiNodeStep ensures that multiNode.Step sends MsgProp to propc
+// chan and other kinds of messages to recvc chan.
+func TestMultiNodeStep(t *testing.T) {
+	for i, msgn := range raftpb.MessageType_name {
+		mn := &multiNode{
+			propc: make(chan multiMessage, 1),
+			recvc: make(chan multiMessage, 1),
+		}
+		msgt := raftpb.MessageType(i)
+		mn.Step(context.TODO(), 1, raftpb.Message{Type: msgt})
+		// Proposal goes to proc chan. Others go to recvc chan.
+		if msgt == raftpb.MsgProp {
+			select {
+			case <-mn.propc:
+			default:
+				t.Errorf("%d: cannot receive %s on propc chan", msgt, msgn)
+			}
+		} else {
+			if msgt == raftpb.MsgBeat || msgt == raftpb.MsgHup || msgt == raftpb.MsgUnreachable || msgt == raftpb.MsgSnapStatus {
+				select {
+				case <-mn.recvc:
+					t.Errorf("%d: step should ignore %s", msgt, msgn)
+				default:
+				}
+			} else {
+				select {
+				case <-mn.recvc:
+				default:
+					t.Errorf("%d: cannot receive %s on recvc chan", msgt, msgn)
+				}
+			}
+		}
+	}
+}
+
+// Cancel and Stop should unblock Step()
+func TestMultiNodeStepUnblock(t *testing.T) {
+	// a node without buffer to block step
+	mn := &multiNode{
+		propc: make(chan multiMessage),
+		done:  make(chan struct{}),
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	stopFunc := func() { close(mn.done) }
+
+	tests := []struct {
+		unblock func()
+		werr    error
+	}{
+		{stopFunc, ErrStopped},
+		{cancel, context.Canceled},
+	}
+
+	for i, tt := range tests {
+		errc := make(chan error, 1)
+		go func() {
+			err := mn.Step(ctx, 1, raftpb.Message{Type: raftpb.MsgProp})
+			errc <- err
+		}()
+		tt.unblock()
+		select {
+		case err := <-errc:
+			if err != tt.werr {
+				t.Errorf("#%d: err = %v, want %v", i, err, tt.werr)
+			}
+			//clean up side-effect
+			if ctx.Err() != nil {
+				ctx = context.TODO()
+			}
+			select {
+			case <-mn.done:
+				mn.done = make(chan struct{})
+			default:
+			}
+		case <-time.After(time.Millisecond * 100):
+			t.Errorf("#%d: failed to unblock step", i)
+		}
+	}
+}
+
+// TestMultiNodePropose ensures that node.Propose sends the given proposal to the underlying raft.
+func TestMultiNodePropose(t *testing.T) {
+	mn := newMultiNode(1, 10, 1)
+	go mn.run()
+	s := NewMemoryStorage()
+	mn.CreateGroup(1, []Peer{{ID: 1}}, s)
+	mn.Campaign(context.TODO(), 1)
+	proposed := false
+	for {
+		rds := <-mn.Ready()
+		rd := rds[1]
+		s.Append(rd.Entries)
+		// Once we are the leader, propose a command.
+		if !proposed && rd.SoftState.Lead == mn.id {
+			mn.Propose(context.TODO(), 1, []byte("somedata"))
+			proposed = true
+		}
+		mn.Advance(rds)
+
+		// Exit when we have three entries: one ConfChange, one no-op for the election,
+		// and our proposed command.
+		lastIndex, err := s.LastIndex()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if lastIndex >= 3 {
+			break
+		}
+	}
+	mn.Stop()
+
+	lastIndex, err := s.LastIndex()
+	if err != nil {
+		t.Fatal(err)
+	}
+	entries, err := s.Entries(lastIndex, lastIndex+1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(entries) != 1 {
+		t.Fatalf("len(entries) = %d, want %d", len(entries), 1)
+	}
+	if !bytes.Equal(entries[0].Data, []byte("somedata")) {
+		t.Errorf("entries[0].Data = %v, want %v", entries[0].Data, []byte("somedata"))
+	}
+}
+
+// TestMultiNodeProposeConfig ensures that multiNode.ProposeConfChange
+// sends the given configuration proposal to the underlying raft.
+func TestMultiNodeProposeConfig(t *testing.T) {
+	mn := newMultiNode(1, 10, 1)
+	go mn.run()
+	s := NewMemoryStorage()
+	mn.CreateGroup(1, []Peer{{ID: 1}}, s)
+	mn.Campaign(context.TODO(), 1)
+	proposed := false
+	var lastIndex uint64
+	var ccdata []byte
+	for {
+		rds := <-mn.Ready()
+		rd := rds[1]
+		s.Append(rd.Entries)
+		// change the step function to appendStep until this raft becomes leader
+		if !proposed && rd.SoftState.Lead == mn.id {
+			cc := raftpb.ConfChange{Type: raftpb.ConfChangeAddNode, NodeID: 1}
+			var err error
+			ccdata, err = cc.Marshal()
+			if err != nil {
+				t.Fatal(err)
+			}
+			mn.ProposeConfChange(context.TODO(), 1, cc)
+			proposed = true
+		}
+		mn.Advance(rds)
+
+		var err error
+		lastIndex, err = s.LastIndex()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if lastIndex >= 3 {
+			break
+		}
+	}
+	mn.Stop()
+
+	entries, err := s.Entries(lastIndex, lastIndex+1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(entries) != 1 {
+		t.Fatalf("len(entries) = %d, want %d", len(entries), 1)
+	}
+	if entries[0].Type != raftpb.EntryConfChange {
+		t.Fatalf("type = %v, want %v", entries[0].Type, raftpb.EntryConfChange)
+	}
+	if !bytes.Equal(entries[0].Data, ccdata) {
+		t.Errorf("data = %v, want %v", entries[0].Data, ccdata)
+	}
+}
+
+// TestBlockProposal from node_test.go has no equivalent in multiNode
+// because we cannot block proposals based on individual group leader status.
+
+// TestNodeTick from node_test.go has no equivalent in multiNode because
+// it reaches into the raft object which is not exposed.
+
+// TestMultiNodeStop ensures that multiNode.Stop() blocks until the node has stopped
+// processing, and that it is idempotent
+func TestMultiNodeStop(t *testing.T) {
+	mn := newMultiNode(1, 10, 1)
+	donec := make(chan struct{})
+
+	go func() {
+		mn.run()
+		close(donec)
+	}()
+
+	mn.Tick()
+	mn.Stop()
+
+	select {
+	case <-donec:
+	case <-time.After(time.Second):
+		t.Fatalf("timed out waiting for node to stop!")
+	}
+
+	// Further ticks should have no effect, the node is stopped.
+	// There is no way to verify this in multinode but at least we can test
+	// it doesn't block or panic.
+	mn.Tick()
+	// Subsequent Stops should have no effect.
+	mn.Stop()
+}
+
+// TestMultiNodeStart ensures that a node can be started correctly. The node should
+// start with correct configuration change entries, and can accept and commit
+// proposals.
+func TestMultiNodeStart(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	cc := raftpb.ConfChange{Type: raftpb.ConfChangeAddNode, NodeID: 1}
+	ccdata, err := cc.Marshal()
+	if err != nil {
+		t.Fatalf("unexpected marshal error: %v", err)
+	}
+	wants := []Ready{
+		{
+			SoftState: &SoftState{Lead: 1, RaftState: StateLeader},
+			HardState: raftpb.HardState{Term: 2, Commit: 2},
+			Entries: []raftpb.Entry{
+				{Type: raftpb.EntryConfChange, Term: 1, Index: 1, Data: ccdata},
+				{Term: 2, Index: 2},
+			},
+			CommittedEntries: []raftpb.Entry{
+				{Type: raftpb.EntryConfChange, Term: 1, Index: 1, Data: ccdata},
+				{Term: 2, Index: 2},
+			},
+		},
+		{
+			HardState:        raftpb.HardState{Term: 2, Commit: 3},
+			Entries:          []raftpb.Entry{{Term: 2, Index: 3, Data: []byte("foo")}},
+			CommittedEntries: []raftpb.Entry{{Term: 2, Index: 3, Data: []byte("foo")}},
+		},
+	}
+	mn := StartMultiNode(1, 10, 1)
+	storage := NewMemoryStorage()
+	mn.CreateGroup(1, []Peer{{ID: 1}}, storage)
+	mn.Campaign(ctx, 1)
+	gs := <-mn.Ready()
+	g := gs[1]
+	if !reflect.DeepEqual(g, wants[0]) {
+		t.Fatalf("#%d: g = %+v,\n             w   %+v", 1, g, wants[0])
+	} else {
+		storage.Append(g.Entries)
+		mn.Advance(gs)
+	}
+
+	mn.Propose(ctx, 1, []byte("foo"))
+	if gs2 := <-mn.Ready(); !reflect.DeepEqual(gs2[1], wants[1]) {
+		t.Errorf("#%d: g = %+v,\n             w   %+v", 2, gs2[1], wants[1])
+	} else {
+		storage.Append(gs2[1].Entries)
+		mn.Advance(gs2)
+	}
+
+	select {
+	case rd := <-mn.Ready():
+		t.Errorf("unexpected Ready: %+v", rd)
+	case <-time.After(time.Millisecond):
+	}
+}
+
+func TestMultiNodeRestart(t *testing.T) {
+	entries := []raftpb.Entry{
+		{Term: 1, Index: 1},
+		{Term: 1, Index: 2, Data: []byte("foo")},
+	}
+	st := raftpb.HardState{Term: 1, Commit: 1}
+
+	want := Ready{
+		HardState: emptyState,
+		// commit up to index commit index in st
+		CommittedEntries: entries[:st.Commit],
+	}
+
+	storage := NewMemoryStorage()
+	storage.SetHardState(st)
+	storage.Append(entries)
+	mn := StartMultiNode(1, 10, 1)
+	mn.CreateGroup(1, nil, storage)
+	gs := <-mn.Ready()
+	if !reflect.DeepEqual(gs[1], want) {
+		t.Errorf("g = %+v,\n             w   %+v", gs[1], want)
+	}
+	mn.Advance(gs)
+
+	select {
+	case rd := <-mn.Ready():
+		t.Errorf("unexpected Ready: %+v", rd)
+	case <-time.After(time.Millisecond):
+	}
+	mn.Stop()
+}
+
+func TestMultiNodeRestartFromSnapshot(t *testing.T) {
+	snap := raftpb.Snapshot{
+		Metadata: raftpb.SnapshotMetadata{
+			ConfState: raftpb.ConfState{Nodes: []uint64{1, 2}},
+			Index:     2,
+			Term:      1,
+		},
+	}
+	entries := []raftpb.Entry{
+		{Term: 1, Index: 3, Data: []byte("foo")},
+	}
+	st := raftpb.HardState{Term: 1, Commit: 3}
+
+	want := Ready{
+		HardState: emptyState,
+		// commit up to index commit index in st
+		CommittedEntries: entries,
+	}
+
+	s := NewMemoryStorage()
+	s.SetHardState(st)
+	s.ApplySnapshot(snap)
+	s.Append(entries)
+	mn := StartMultiNode(1, 10, 1)
+	mn.CreateGroup(1, nil, s)
+	if gs := <-mn.Ready(); !reflect.DeepEqual(gs[1], want) {
+		t.Errorf("g = %+v,\n             w   %+v", gs[1], want)
+	} else {
+		mn.Advance(gs)
+	}
+
+	select {
+	case rd := <-mn.Ready():
+		t.Errorf("unexpected Ready: %+v", rd)
+	case <-time.After(time.Millisecond):
+	}
+}
+
+func TestMultiNodeAdvance(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	storage := NewMemoryStorage()
+	mn := StartMultiNode(1, 10, 1)
+	mn.CreateGroup(1, []Peer{{ID: 1}}, storage)
+	mn.Campaign(ctx, 1)
+	rd1 := <-mn.Ready()
+	mn.Propose(ctx, 1, []byte("foo"))
+	select {
+	case rd2 := <-mn.Ready():
+		t.Fatalf("unexpected Ready before Advance: %+v", rd2)
+	case <-time.After(time.Millisecond):
+	}
+	storage.Append(rd1[1].Entries)
+	mn.Advance(rd1)
+	select {
+	case <-mn.Ready():
+	case <-time.After(time.Millisecond):
+		t.Errorf("expect Ready after Advance, but there is no Ready available")
+	}
+}