fix: make data syncer run configurable on mode (2->3) change (#104401)

pkg/apiserver/rest/dualwriter.go

@@ -164,6 +164,10 @@ func SetDualWritingMode(
 			return Mode0, errDualWriterSetCurrentMode
 		}
 	case cfg.Mode >= Mode3 && currentMode < Mode3:
+		if cfg.SkipDataSync {
+			return currentMode, nil
+		}
+
 		// Transitioning to Mode3 or higher requires data synchronization.
 		cfgModeTmp := cfg.Mode
 		// Before running the sync, set the syncer config to the current mode, as we have to run the syncer

pkg/apiserver/rest/dualwriter_syncer.go

@@ -36,6 +36,7 @@ type SyncerConfig struct {
 	LegacyStorage     Storage
 	Storage           Storage
 	ServerLockService ServerLockService
+	SkipDataSync      bool
 
 	DataSyncerInterval     time.Duration
 	DataSyncerRecordsLimit int

pkg/apiserver/rest/dualwriter_test.go

@@ -20,6 +20,7 @@ func TestSetDualWritingMode(t *testing.T) {
 		kvStore         *fakeNamespacedKV
 		desiredMode     DualWriterMode
 		expectedMode    DualWriterMode
+		skipDataSync    bool
 		serverLockError error
 	}
 	tests :=
@@ -61,6 +62,13 @@ func TestSetDualWritingMode(t *testing.T) {
 				expectedMode:    Mode2,
 				serverLockError: fmt.Errorf("lock already exists"),
 			},
+			{
+				name:         "should keep mode2 when trying to go from mode2 to mode3 and migration is disabled",
+				kvStore:      &fakeNamespacedKV{data: map[string]string{"playlist.grafana.app/playlists": "2"}, namespace: "storage.dualwriting"},
+				desiredMode:  Mode3,
+				expectedMode: Mode2,
+				skipDataSync: true,
+			},
 		}
 
 	for _, tt := range tests {
@@ -86,6 +94,7 @@ func TestSetDualWritingMode(t *testing.T) {
 			Storage:           us,
 			Kind:              "playlist.grafana.app/playlists",
 			Mode:              tt.desiredMode,
+			SkipDataSync:      tt.skipDataSync,
 			ServerLockService: serverLockSvc,
 			RequestInfo:       &request.RequestInfo{},
 			Reg:               p,