Disallow -v2-deprecation>'not-yet' combined with --enable-v2

server/etcdserver/server.go

@@ -479,6 +479,11 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 				cfg.Logger.Panic("failed to recover from snapshot", zap.Error(err))
 			}
 
+			if err = assertNoV2StoreContent(cfg.Logger, st, cfg.V2Deprecation); err != nil {
+				cfg.Logger.Error("illegal v2store content", zap.Error(err))
+				return nil, err
+			}
+
 			cfg.Logger.Info(
 				"recovered v2 store from snapshot",
 				zap.Uint64("snapshot-index", snapshot.Metadata.Index),
@@ -496,6 +501,8 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 				zap.Int64("backend-size-in-use-bytes", s2),
 				zap.String("backend-size-in-use", humanize.Bytes(uint64(s2))),
 			)
+		} else {
+			cfg.Logger.Info("No snapshot found. Recovering WAL from scratch!")
 		}
 
 		if !cfg.ForceNewCluster {
@@ -662,6 +669,23 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 	return srv, nil
 }
 
+// assertNoV2StoreContent -> depending on the deprecation stage, warns or report an error
+// if the v2store contains custom content.
+func assertNoV2StoreContent(lg *zap.Logger, st v2store.Store, deprecationStage config.V2DeprecationEnum) error {
+	metaOnly, err := membership.IsMetaStoreOnly(st)
+	if err != nil {
+		return err
+	}
+	if metaOnly {
+		return nil
+	}
+	if deprecationStage.IsAtLeast(config.V2_DEPR_1_WRITE_ONLY) {
+		return fmt.Errorf("detected disallowed custom content in v2store for stage --v2-deprecation=%s", deprecationStage)
+	}
+	lg.Warn("detected custom v2store content. Etcd v3.5 is the last version allowing to access it using API v2. Please remove the content.")
+	return nil
+}
+
 func (s *EtcdServer) Logger() *zap.Logger {
 	s.lgMu.RLock()
 	l := s.lg
@@ -1252,6 +1276,10 @@ func (s *EtcdServer) applySnapshot(ep *etcdProgress, apply *apply) {
 		lg.Panic("failed to restore v2 store", zap.Error(err))
 	}
 
+	if err := assertNoV2StoreContent(lg, s.v2store, s.Cfg.V2Deprecation); err != nil {
+		lg.Panic("illegal v2store content", zap.Error(err))
+	}
+
 	lg.Info("restored v2 store")
 
 	s.cluster.SetBackend(newbe)