applyV2 should reapply on backend only once

During review of: etcd-io#12988 spotted that PUT is actially writing to v3-backend. If we are replaying WAL log, it might happened that backend's applied_index is > than the WAL's log entry. In such situation we should skip applying on backend V3. I think both the methods (setVersion, setMembersAttributes) are in practice idempotent so its not that 'serious' problem, but for formal correctness adding the proper checks.
ptabor · May 18, 2021 · 7ddc076 · 7ddc076
1 parent 80ccb27
commit 7ddc076
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Showing 3 changed files with 10 additions and 9 deletions.
diff --git a/server/etcdserver/apply_v2.go b/server/etcdserver/apply_v2.go
@@ -36,7 +36,7 @@ const v2Version = "v2"
 type ApplierV2 interface {
 	Delete(r *RequestV2) Response
 	Post(r *RequestV2) Response
-	Put(r *RequestV2) Response
+	Put(r *RequestV2, shouldApplyV3 membership.ShouldApplyV3) Response
 	QGet(r *RequestV2) Response
 	Sync(r *RequestV2) Response
 }
@@ -67,7 +67,7 @@ func (a *applierV2store) Post(r *RequestV2) Response {
 	return toResponse(a.store.Create(r.Path, r.Dir, r.Val, true, r.TTLOptions()))
 }
 
-func (a *applierV2store) Put(r *RequestV2) Response {
+func (a *applierV2store) Put(r *RequestV2, shouldApplyV3 membership.ShouldApplyV3) Response {
 	ttlOptions := r.TTLOptions()
 	exists, existsSet := pbutil.GetBool(r.PrevExist)
 	switch {
@@ -89,7 +89,7 @@ func (a *applierV2store) Put(r *RequestV2) Response {
 				a.lg.Panic("failed to unmarshal", zap.String("value", r.Val), zap.Error(err))
 			}
 			if a.cluster != nil {
-				a.cluster.UpdateAttributes(id, attr, true)
+				a.cluster.UpdateAttributes(id, attr, shouldApplyV3)
 			}
 			// return an empty response since there is no consumer.
 			return Response{}
@@ -98,7 +98,7 @@ func (a *applierV2store) Put(r *RequestV2) Response {
 		if r.Path == membership.StoreClusterVersionKey() {
 			if a.cluster != nil {
 				// persist to backend given v2store can be very stale
-				a.cluster.SetVersion(semver.Must(semver.NewVersion(r.Val)), api.UpdateCapability, membership.ApplyBoth)
+				a.cluster.SetVersion(semver.Must(semver.NewVersion(r.Val)), api.UpdateCapability, shouldApplyV3)
 			}
 			return Response{}
 		}
@@ -117,7 +117,7 @@ func (a *applierV2store) Sync(r *RequestV2) Response {
 
 // applyV2Request interprets r as a call to v2store.X
 // and returns a Response interpreted from v2store.Event
-func (s *EtcdServer) applyV2Request(r *RequestV2) (resp Response) {
+func (s *EtcdServer) applyV2Request(r *RequestV2, shouldApplyV3 membership.ShouldApplyV3) (resp Response) {
 	stringer := panicAlternativeStringer{
 		stringer:    r,
 		alternative: func() string { return fmt.Sprintf("id:%d,method:%s,path:%s", r.ID, r.Method, r.Path) },
@@ -132,7 +132,7 @@ func (s *EtcdServer) applyV2Request(r *RequestV2) (resp Response) {
 	case "POST":
 		return s.applyV2.Post(r)
 	case "PUT":
-		return s.applyV2.Put(r)
+		return s.applyV2.Put(r, shouldApplyV3)
 	case "DELETE":
 		return s.applyV2.Delete(r)
 	case "QGET":

diff --git a/server/etcdserver/server.go b/server/etcdserver/server.go
@@ -2181,14 +2181,14 @@ func (s *EtcdServer) applyEntryNormal(e *raftpb.Entry) {
 		rp := &r
 		pbutil.MustUnmarshal(rp, e.Data)
 		s.lg.Debug("applyEntryNormal", zap.Stringer("V2request", rp))
-		s.w.Trigger(r.ID, s.applyV2Request((*RequestV2)(rp)))
+		s.w.Trigger(r.ID, s.applyV2Request((*RequestV2)(rp), shouldApplyV3))
 		return
 	}
 	s.lg.Debug("applyEntryNormal", zap.Stringer("raftReq", &raftReq))
 
 	if raftReq.V2 != nil {
 		req := (*RequestV2)(raftReq.V2)
-		s.w.Trigger(req.ID, s.applyV2Request(req))
+		s.w.Trigger(req.ID, s.applyV2Request(req, shouldApplyV3))
 		return
 	}
 

diff --git a/server/etcdserver/v2_server.go b/server/etcdserver/v2_server.go
@@ -19,6 +19,7 @@ import (
 	"time"
 
 	pb "go.etcd.io/etcd/api/v3/etcdserverpb"
+	"go.etcd.io/etcd/server/v3/etcdserver/api/membership"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v2store"
 )
 
@@ -52,7 +53,7 @@ func (a *reqV2HandlerStore) Post(ctx context.Context, r *RequestV2) (Response, e
 }
 
 func (a *reqV2HandlerStore) Put(ctx context.Context, r *RequestV2) (Response, error) {
-	return a.applier.Put(r), nil
+	return a.applier.Put(r, membership.ApplyBoth), nil
 }
 
 func (a *reqV2HandlerStore) Delete(ctx context.Context, r *RequestV2) (Response, error) {