DualWrite: Cleanup and centralize the dual write creation (#90013)

pkg/apiserver/rest/dualwriter.go

@@ -11,6 +11,7 @@ import (
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apiserver/pkg/registry/rest"
 	"k8s.io/klog/v2"
 )
@@ -25,6 +26,9 @@ var (
 	_ rest.SingularNameProvider = (DualWriter)(nil)
 )
 
+// Function that will create a dual writer
+type DualWriteBuilder func(gr schema.GroupResource, legacy LegacyStorage, storage Storage) (Storage, error)
+
 // Storage is a storage implementation that satisfies the same interfaces as genericregistry.Store.
 type Storage interface {
 	rest.Storage
@@ -152,7 +156,12 @@ func SetDualWritingMode(
 	entity string,
 	desiredMode DualWriterMode,
 	reg prometheus.Registerer,
-) (DualWriter, error) {
+) (DualWriterMode, error) {
+	// Mode0 means no DualWriter
+	if desiredMode == Mode0 {
+		return Mode0, nil
+	}
+
 	toMode := map[string]DualWriterMode{
 		// It is not possible to initialize a mode 0 dual writer. Mode 0 represents
 		// writing to legacy storage without `unifiedStorage` enabled.
@@ -166,7 +175,7 @@ func SetDualWritingMode(
 	// Use entity name as key
 	m, ok, err := kvs.Get(ctx, entity)
 	if err != nil {
-		return nil, errors.New("failed to fetch current dual writing mode")
+		return Mode0, errors.New("failed to fetch current dual writing mode")
 	}
 
 	currentMode, valid := toMode[m]
@@ -182,7 +191,7 @@ func SetDualWritingMode(
 
 		err := kvs.Set(ctx, entity, fmt.Sprint(currentMode))
 		if err != nil {
-			return nil, errDualWriterSetCurrentMode
+			return Mode0, errDualWriterSetCurrentMode
 		}
 	}
 
@@ -194,7 +203,7 @@ func SetDualWritingMode(
 
 		err := kvs.Set(ctx, entity, fmt.Sprint(currentMode))
 		if err != nil {
-			return nil, errDualWriterSetCurrentMode
+			return Mode0, errDualWriterSetCurrentMode
 		}
 	}
 	if (desiredMode == Mode1) && (currentMode == Mode2) {
@@ -204,13 +213,13 @@ func SetDualWritingMode(
 
 		err := kvs.Set(ctx, entity, fmt.Sprint(currentMode))
 		if err != nil {
-			return nil, errDualWriterSetCurrentMode
+			return Mode0, errDualWriterSetCurrentMode
 		}
 	}
 
 	// 	#TODO add support for other combinations of desired and current modes
 
-	return NewDualWriter(currentMode, legacy, storage, reg), nil
+	return currentMode, nil
 }
 
 var defaultConverter = runtime.UnstructuredConverter(runtime.DefaultUnstructuredConverter)

pkg/apiserver/rest/dualwriter_test.go

@@ -46,9 +46,9 @@ func TestSetDualWritingMode(t *testing.T) {
 		kvStore := &fakeNamespacedKV{data: make(map[string]string), namespace: "storage.dualwriting." + tt.stackID}
 
 		p := prometheus.NewRegistry()
-		dw, err := SetDualWritingMode(context.Background(), kvStore, ls, us, "playlist.grafana.app/v0alpha1", tt.desiredMode, p)
+		dwMode, err := SetDualWritingMode(context.Background(), kvStore, ls, us, "playlist.grafana.app/v0alpha1", tt.desiredMode, p)
 		assert.NoError(t, err)
-		assert.Equal(t, tt.expectedMode, dw.Mode())
+		assert.Equal(t, tt.expectedMode, dwMode)
 
 		// check kv store
 		val, ok, err := kvStore.Get(context.Background(), "playlist.grafana.app/v0alpha1")