Fix ILB forwarding rule bug

pkg/loadbalancers/features/l7ilb.go

@@ -65,6 +65,23 @@ func isSameNetwork(l, r string) (bool, error) {
 	return lID.Equal(rID), nil
 }
 
+// IsCustomModeNetwork is a helper for determining if a network is a custom mode network
+// (as opposed to a auto mode network).  This is used for l7-ilb since custom mode networks
+// require an additional field on the forwarding rule
+func IsCustomModeNetwork(c *gce.Cloud, networkURL string) (bool, error) {
+	netID, err := cloud.ParseResourceURL(networkURL)
+	if err != nil {
+		return false, err
+	}
+
+	network, err := c.Compute().Networks().Get(context.Background(), netID.Key)
+	if err != nil {
+		return false, err
+	}
+
+	return !network.AutoCreateSubnetworks, nil
+}
+
 // L7ILBVersion is a helper to get the version of L7-ILB
 func L7ILBVersions() *ResourceVersions {
 	return versionsFromFeatures([]string{FeatureL7ILB})

pkg/loadbalancers/forwarding_rules.go

@@ -18,6 +18,8 @@ package loadbalancers
 
 import (
 	"fmt"
+	"k8s.io/ingress-gce/pkg/flags"
+	"k8s.io/ingress-gce/pkg/loadbalancers/features"
 
 	"k8s.io/ingress-gce/pkg/composite"
 	"k8s.io/ingress-gce/pkg/utils"
@@ -91,9 +93,17 @@ func (l *L7) checkForwardingRule(name, proxyLink, ip, portRange string) (fw *com
 		}
 
 		// Update rule for L7-ILB
-		if utils.IsGCEL7ILBIngress(l.runtimeInfo.Ingress) {
+		if flags.F.EnableL7Ilb && utils.IsGCEL7ILBIngress(l.runtimeInfo.Ingress) {
 			rule.LoadBalancingScheme = "INTERNAL_MANAGED"
+
+			// Custom mode networks require adding the cluster subnetwork
+			if isCustomMode, err := features.IsCustomModeNetwork(l.cloud, l.cloud.NetworkURL()); err != nil {
+				return nil, err
+			} else if isCustomMode {
+				rule.Subnetwork = l.cloud.SubnetworkURL()
+			}
 		}
+
 		if err = composite.CreateForwardingRule(l.cloud, key, rule); err != nil {
 			return nil, err
 		}