Storage: Read desired mode from config instead of feature flags (#88353)

* Read desired mode from config
* Update playlist integration tests
* Add mode 1 playlist integration tests
* Add mode 0 dual writing to playlist integration tests
* Add documentation for the different dual writing modes

pkg/apiserver/builder/common.go

@@ -3,6 +3,7 @@ package builder
 import (
 	"net/http"
 
+	grafanarest "github.com/grafana/grafana/pkg/apiserver/rest"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/runtime/serializer"
@@ -27,7 +28,7 @@ type APIGroupBuilder interface {
 		scheme *runtime.Scheme,
 		codecs serializer.CodecFactory,
 		optsGetter generic.RESTOptionsGetter,
-		dualWrite bool,
+		desiredMode grafanarest.DualWriterMode,
 	) (*genericapiserver.APIGroupInfo, error)
 
 	// Get OpenAPI definitions
@@ -40,6 +41,11 @@ type APIGroupBuilder interface {
 	// Standard namespace checking will happen before this is called, specifically
 	// the namespace must matches an org|stack that the user belongs to
 	GetAuthorizer() authorizer.Authorizer
+
+	// Get the desired dual writing mode. These are modes 1, 2, 3 and 4 if
+	// the feature flag `unifiedStorage` is enabled and mode 0 if it is not enabled.
+	// #TODO add type for map[string]grafanarest.DualWriterMode?
+	GetDesiredDualWriterMode(dualWrite bool, toMode map[string]grafanarest.DualWriterMode) grafanarest.DualWriterMode
 }
 
 // Builders that implement OpenAPIPostProcessor are given a chance to modify the schema directly

pkg/apiserver/builder/helper.go

@@ -24,6 +24,7 @@ import (
 	"k8s.io/kube-openapi/pkg/common"
 
 	"github.com/grafana/grafana/pkg/apiserver/endpoints/filters"
+	"github.com/grafana/grafana/pkg/services/apiserver/options"
 )
 
 // TODO: this is a temporary hack to make rest.Connecter work with resource level routes
@@ -126,10 +127,16 @@ func InstallAPIs(
 	server *genericapiserver.GenericAPIServer,
 	optsGetter generic.RESTOptionsGetter,
 	builders []APIGroupBuilder,
-	dualWrite bool,
+	storageOpts *options.StorageOptions,
 ) error {
+	// dual writing is only enabled when the storage type is not legacy.
+	// this is needed to support setting a default RESTOptionsGetter for new APIs that don't
+	// support the legacy storage type.
+	dualWriteEnabled := storageOpts.StorageType != options.StorageTypeLegacy
+
 	for _, b := range builders {
-		g, err := b.GetAPIGroupInfo(scheme, codecs, optsGetter, dualWrite)
+		mode := b.GetDesiredDualWriterMode(dualWriteEnabled, storageOpts.DualWriterDesiredModes)
+		g, err := b.GetAPIGroupInfo(scheme, codecs, optsGetter, mode)
 		if err != nil {
 			return err
 		}