GCE load balancer: Stop managing instance groups for internal load balancer if rbs alpha feature gate enable

use multiple instance groups if present

staging/src/k8s.io/legacy-cloud-providers/gce/gce_alpha.go

@@ -23,6 +23,10 @@ const (
 	// AlphaFeatureILBSubsets allows InternalLoadBalancer services to include a subset
 	// of cluster nodes as backends instead of all nodes.
 	AlphaFeatureILBSubsets = "ILBSubsets"
+
+	// AlphaFeatureNetLBRbs enabled L4 Regional Backend Services and
+	// disables instance group management in service controller
+	AlphaFeatureNetLBRbs = "NetLB_RBS"
 )
 
 // AlphaFeatureGate contains a mapping of alpha features to whether they are enabled

staging/src/k8s.io/legacy-cloud-providers/gce/gce_instancegroup.go

@@ -50,6 +50,16 @@ func (g *Cloud) DeleteInstanceGroup(name string, zone string) error {
 	return mc.Observe(g.c.InstanceGroups().Delete(ctx, meta.ZonalKey(name, zone)))
 }
 
+// FilterInstanceGroupsByName lists all InstanceGroups in the project and
+// zone that match the name regexp.
+func (g *Cloud) FilterInstanceGroupsByName(name, zone string) ([]*compute.InstanceGroup, error) {
+	ctx, cancel := cloud.ContextWithCallTimeout()
+	defer cancel()
+	mc := newInstanceGroupMetricContext("list", zone)
+	v, err := g.c.InstanceGroups().List(ctx, zone, filter.Regexp("name", name))
+	return v, mc.Observe(err)
+}
+
 // ListInstanceGroups lists all InstanceGroups in the project and
 // zone.
 func (g *Cloud) ListInstanceGroups(zone string) ([]*compute.InstanceGroup, error) {

staging/src/k8s.io/legacy-cloud-providers/gce/gce_loadbalancer_internal.go

@@ -625,11 +625,21 @@ func (g *Cloud) ensureInternalInstanceGroups(name string, nodes []*v1.Node) ([]s
 	klog.V(2).Infof("ensureInternalInstanceGroups(%v): %d nodes over %d zones in region %v", name, len(nodes), len(zonedNodes), g.region)
 	var igLinks []string
 	for zone, nodes := range zonedNodes {
-		igLink, err := g.ensureInternalInstanceGroup(name, zone, nodes)
+		if g.AlphaFeatureGate.Enabled(AlphaFeatureNetLBRbs) {
-		if err != nil {
+			igs, err := g.FilterInstanceGroupsByName(name, zone)
-			return []string{}, err
+			if err != nil {
+				return []string{}, err
+			}
+			for _, ig := range igs {
+				igLinks = append(igLinks, ig.SelfLink)
+			}
+		} else {
+			igLink, err := g.ensureInternalInstanceGroup(name, zone, nodes)
+			if err != nil {
+				return []string{}, err
+			}
+			igLinks = append(igLinks, igLink)
 		}
-		igLinks = append(igLinks, igLink)
 	}
 
 	return igLinks, nil