[release-3.5] [Solution 2] Auto sync members in v3store if Islearner is the only field that differs between v2store and v3store

server/embed/etcd.go

@@ -277,6 +277,9 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 			return e, err
 		}
 	}
+
+	e.Server.SyncLearnerPromotionIfNeeded()
+
 	e.Server.Start()
 
 	if err = e.servePeers(); err != nil {

server/etcdserver/api/membership/cluster.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"path"
+	"reflect"
 	"sort"
 	"strings"
 	"sync"
@@ -530,8 +531,22 @@ func (c *RaftCluster) PromoteMember(id types.ID, shouldApplyV3 ShouldApplyV3) {
 	if c.v2store != nil {
 		mustUpdateMemberInStore(c.lg, c.v2store, c.members[id])
 	}
-	if c.be != nil && shouldApplyV3 {
-		unsafeSaveMemberToBackend(c.lg, c.be, c.members[id])
+	if c.be != nil {
+		if shouldApplyV3 {
+			unsafeSaveMemberToBackend(c.lg, c.be, c.members[id])
+		} else {
+			// Workaround https://github.com/etcd-io/etcd/issues/19557 for the case that
+			// learner promotion hasn't been applied.
+			v3Members, _ := membersFromBackend(c.lg, c.be)
+			if m, ok := v3Members[id]; ok {
+				if m.IsLearner {
+					c.lg.Info("Forcibly apply member promotion", zap.String("member", fmt.Sprintf("%+v", *c.members[id])))
+					unsafeHackySaveMemberToBackend(c.lg, c.be, c.members[id])
+				} else {
+					c.lg.Info("Member promotion had already been correctly applied", zap.String("member", fmt.Sprintf("%+v", *c.members[id])))
+				}
+			}
+		}
 	}
 
 	c.lg.Info(
@@ -542,6 +557,53 @@ func (c *RaftCluster) PromoteMember(id types.ID, shouldApplyV3 ShouldApplyV3) {
 	)
 }
 
+func (c *RaftCluster) SyncLearnerPromotionIfNeeded() {
+	c.Lock()
+	defer c.Unlock()
+
+	v2Members, _ := membersFromStore(c.lg, c.v2store)
+	v3Members, _ := membersFromBackend(c.lg, c.be)
+
+	for id, v2Member := range v2Members {
+		v3Member, ok := v3Members[id]
+
+		if !ok {
+			c.lg.Error("Detected member only in v2store but missing in v3store", zap.String("member", fmt.Sprintf("%+v", *v2Member)))
+			continue
+		}
+
+		// A peerURL list is considered the same regardless of order.
+		clonedV2Member := v2Member.Clone()
+		sort.Strings(clonedV2Member.PeerURLs)
+
+		clonedV3Member := v3Member.Clone()
+		sort.Strings(clonedV3Member.PeerURLs)
+
+		if reflect.DeepEqual(clonedV2Member.RaftAttributes, clonedV3Member.RaftAttributes) {
+			c.lg.Info("Member's RaftAttributes is consistent between v2store and v3store", zap.String("member", fmt.Sprintf("%+v", *v2Member)))
+			continue
+		}
+
+		// Sync member iff both conditions below are true,
+		//  1. IsLearner is the only field in RaftAttributes that differs between v2store and v3store.
+		//  2. v2store.IsLearner == false && v3store.IsLearner == true.
+		clonedV3Member.IsLearner = false
+		if reflect.DeepEqual(clonedV2Member.RaftAttributes, clonedV3Member.RaftAttributes) {
+			syncedV3Member := v3Member.Clone()
+			syncedV3Member.IsLearner = false
+			c.lg.Warn("Syncing member in v3store", zap.String("member", fmt.Sprintf("%+v", *syncedV3Member)))
+			unsafeHackySaveMemberToBackend(c.lg, c.be, syncedV3Member)
+			c.be.ForceCommit()
+			continue
+		}
+
+		c.lg.Error("Cannot sync member in v3store due to IsLearner not being the only field that differs between v2store amd v3store",
+			zap.String("v2member", fmt.Sprintf("%+v", *v2Member)),
+			zap.String("v3member", fmt.Sprintf("%+v", *v3Member)),
+		)
+	}
+}
+
 func (c *RaftCluster) UpdateRaftAttributes(id types.ID, raftAttr RaftAttributes, shouldApplyV3 ShouldApplyV3) {
 	c.Lock()
 	defer c.Unlock()

server/etcdserver/api/membership/cluster_test.go

@@ -24,7 +24,7 @@ import (
 
 	"github.com/coreos/go-semver/semver"
 	"github.com/stretchr/testify/assert"
-	betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
+	"github.com/stretchr/testify/require"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zaptest"
 
@@ -33,6 +33,7 @@ import (
 	"go.etcd.io/etcd/raft/v3/raftpb"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v2store"
 	"go.etcd.io/etcd/server/v3/mock/mockstore"
+	betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
 )
 
 func TestClusterMember(t *testing.T) {
@@ -1210,3 +1211,160 @@ func TestRemoveMemberSyncsBackendAndStoreV2(t *testing.T) {
 		})
 	}
 }
+
+func TestSyncLearnerPromotion(t *testing.T) {
+	tcs := []struct {
+		name string
+
+		storeV2Members []*Member
+		backendMembers []*Member
+
+		expectV3Members map[types.ID]*Member
+	}{
+		{
+			name: "v3store should keep unchanged if IsLearner isn't the only field that differs",
+			storeV2Members: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.100:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+			backendMembers: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: true,
+					},
+				},
+			},
+			expectV3Members: map[types.ID]*Member{
+				100: {
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: true,
+					},
+				},
+			},
+		},
+		{
+			name: "v3store should keep unchanged if IsLearner is the only field that differs but v3store.IsLearner is false",
+			storeV2Members: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: true,
+					},
+				},
+			},
+			backendMembers: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+			expectV3Members: map[types.ID]*Member{
+				100: {
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+		},
+		{
+			name: "v3store should be updated if IsLearner is the only field that differs and v3store.IsLearner is true",
+			storeV2Members: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+			backendMembers: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: true,
+					},
+				},
+			},
+			expectV3Members: map[types.ID]*Member{
+				100: {
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+		},
+		{
+			name: "v3store should be updated if IsLearner is the only field that differs and peerURLs are in different order in v2store and v3store",
+			storeV2Members: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://10.0.0.9:2380", "http://127.0.0.1:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+			backendMembers: []*Member{
+				{
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://127.0.0.1:2380", "http://10.0.0.9:2380"},
+						IsLearner: true,
+					},
+				},
+			},
+			expectV3Members: map[types.ID]*Member{
+				100: {
+					ID: 100,
+					RaftAttributes: RaftAttributes{
+						PeerURLs:  []string{"http://127.0.0.1:2380", "http://10.0.0.9:2380"},
+						IsLearner: false,
+					},
+				},
+			},
+		},
+	}
+	for _, tc := range tcs {
+		t.Run(tc.name, func(t *testing.T) {
+			lg := zaptest.NewLogger(t)
+			be, _ := betesting.NewDefaultTmpBackend(t)
+			defer be.Close()
+			mustCreateBackendBuckets(be)
+			for _, m := range tc.backendMembers {
+				unsafeSaveMemberToBackend(lg, be, m)
+			}
+			be.ForceCommit()
+
+			st := v2store.New()
+			for _, m := range tc.storeV2Members {
+				mustSaveMemberToStore(lg, st, m)
+			}
+
+			cluster := NewCluster(lg)
+			cluster.SetBackend(be)
+			cluster.SetStore(st)
+
+			cluster.SyncLearnerPromotionIfNeeded()
+			v3Members, _ := cluster.MembersFromBackend()
+			require.Equal(t, tc.expectV3Members, v3Members)
+		})
+	}
+}

server/etcdserver/api/membership/store.go

@@ -58,6 +58,22 @@ func unsafeSaveMemberToBackend(lg *zap.Logger, be backend.Backend, m *Member) er
 	return nil
 }
 
+// unsafeHackySaveMemberToBackend updates the member in a hacky way.
+// It's only used to workaround https://github.com/etcd-io/etcd/issues/19557.
+func unsafeHackySaveMemberToBackend(lg *zap.Logger, be backend.Backend, m *Member) error {
+	mkey := backendMemberKey(m.ID)
+	mvalue, err := json.Marshal(m)
+	if err != nil {
+		lg.Panic("failed to marshal member", zap.Error(err))
+	}
+
+	tx := be.BatchTx()
+	tx.LockOutsideApply()
+	defer tx.Unlock()
+	tx.UnsafePut(buckets.Members, mkey, mvalue)
+	return nil
+}
+
 // TrimClusterFromBackend removes all information about cluster (versions)
 // from the v3 backend.
 func TrimClusterFromBackend(be backend.Backend) error {

server/etcdserver/server.go

@@ -2931,3 +2931,15 @@ func maybeDefragBackend(cfg config.ServerConfig, be backend.Backend) error {
 func (s *EtcdServer) CorruptionChecker() CorruptionChecker {
 	return s.corruptionChecker
 }
+
+// SyncLearnerPromotionIfNeeded provides a workaround for the users who have
+// already been affected by https://github.com/etcd-io/etcd/issues/19557.
+// It automatically syncs the v3store (bbolt) from v2store iff all the
+// conditions below are true for each member,
+//  1. IsLearner is the only field that differs between v2store and v3store.
+//  2. v2store.IsLearner == false && v3store.IsLearner == true.
+func (s *EtcdServer) SyncLearnerPromotionIfNeeded() {
+	s.Logger().Info("Trying to sync the learner promotion operations for v3store if needed")
+	s.cluster.SyncLearnerPromotionIfNeeded()
+	s.Logger().Info("Finished syncing the learner promotion operations for v3store")
+}

server/mvcc/backend/verify.go

@@ -61,6 +61,14 @@ func verifyLockEnabled() bool {
 
 func insideApply() bool {
 	stackTraceStr := string(debug.Stack())
+
+	// Exclude the case of `unsafeHackySaveMemberToBackend`, which is
+	// used to workaround the situation which are already affected by
+	// https://github.com/etcd-io/etcd/issues/19557
+	if strings.Contains(stackTraceStr, "unsafeHackySaveMemberToBackend") {
+		return false
+	}
+
 	return strings.Contains(stackTraceStr, ".applyEntries")
 }