Use Patch when syncing GCP BackendService. Linking backend groups still uses Update

pkg/backends/backends.go

@@ -129,6 +129,25 @@ func (b *Backends) Update(be *composite.BackendService) error {
 	return nil
 }
 
+// Patch implements Pool.
+func (b *Backends) Patch(be *composite.BackendService) error {
+	// Ensure the backend service has the proper version before updating.
+	be.Version = features.VersionFromDescription(be.Description)
+	scope, err := composite.ScopeFromSelfLink(be.SelfLink)
+	if err != nil {
+		return err
+	}
+
+	key, err := composite.CreateKey(b.cloud, be.Name, scope)
+	if err != nil {
+		return err
+	}
+	if err := composite.PatchBackendService(b.cloud, key, be); err != nil {
+		return err
+	}
+	return nil
+}
+
 // Get implements Pool.
 func (b *Backends) Get(name string, version meta.Version, scope meta.KeyType) (*composite.BackendService, error) {
 	key, err := composite.CreateKey(b.cloud, name, scope)

pkg/backends/interfaces.go

@@ -39,6 +39,8 @@ type Pool interface {
 	Create(sp utils.ServicePort, hcLink string) (*composite.BackendService, error)
 	// Update a BackendService given the composite type.
 	Update(be *composite.BackendService) error
+	// Patch a BackendService given the composite type.
+	Patch(be *composite.BackendService) error
 	// Delete a BackendService given its name.
 	Delete(name string, version meta.Version, scope meta.KeyType) error
 	// Get the health of a BackendService given its name.