services: add opt-in support for endpointless Cluster LB services

Signed-off-by: Yannick Wahner <thenabsku@gmail.com>

pkg/endpoints/endpoints.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -65,6 +66,8 @@ func (p *Processor) AddOrModify(svcCtx *servicecontext.Context, event watch.Even
 		log.Error("updating instance", "err", err)
 	}
 
+	allowReconcileWithoutEndpoints := shouldAllowReconcileWithoutEndpoints(service)
+
 	// Find out if we have any local endpoints
 	// if out endpoint is empty then populate it
 	// if not, go through the endpoints and see if ours still exists
@@ -115,8 +118,11 @@ func (p *Processor) AddOrModify(svcCtx *servicecontext.Context, event watch.Even
 			}
 		}
 	} else {
-		// There are no local endpoints
-		if svcCtx.Signalled.Load() {
+		if allowReconcileWithoutEndpoints {
+			// Explicit opt-in for controllers that create LoadBalancer services without endpoints
+			svcCtx.SignalReadiness()
+		} else if svcCtx.Signalled.Load() {
+			// There are no local endpoints
 			svcCtx.ResetReadiness()
 			p.worker.clear(svcCtx, lastKnownGoodEndpoint, service)
 			if p.config.EnableARP && !p.config.EnableServicesElection {
@@ -272,6 +278,14 @@ func (p *Processor) startLeaderElection(svcCtx *servicecontext.Context, service
 	}
 }
 
+func shouldAllowReconcileWithoutEndpoints(service *v1.Service) bool {
+	if service == nil || service.Spec.ExternalTrafficPolicy != v1.ServiceExternalTrafficPolicyTypeCluster {
+		return false
+	}
+
+	return strings.EqualFold(service.Annotations[kubevip.AllowReconcileWithoutEndpoints], "true")
+}
+
 func hasV6(endpoints []string) bool {
 	for _, e := range endpoints {
 		ip := net.ParseIP(e)

pkg/endpoints/endpoints_test.go

@@ -0,0 +1,63 @@
+package endpoints
+
+import (
+	"testing"
+
+	"github.com/kube-vip/kube-vip/pkg/kubevip"
+	v1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+func TestShouldAllowReconcileWithoutEndpoints(t *testing.T) {
+	tests := []struct {
+		name     string
+		service  *v1.Service
+		expected bool
+	}{
+		{
+			name:     "nil service",
+			expected: false,
+		},
+		{
+			name: "cluster policy with opt-in annotation",
+			service: &v1.Service{
+				Spec:       v1.ServiceSpec{ExternalTrafficPolicy: v1.ServiceExternalTrafficPolicyTypeCluster},
+				ObjectMeta: metav1.ObjectMeta{Annotations: map[string]string{kubevip.AllowReconcileWithoutEndpoints: "true"}},
+			},
+			expected: true,
+		},
+		{
+			name: "cluster policy with case-insensitive opt-in",
+			service: &v1.Service{
+				Spec:       v1.ServiceSpec{ExternalTrafficPolicy: v1.ServiceExternalTrafficPolicyTypeCluster},
+				ObjectMeta: metav1.ObjectMeta{Annotations: map[string]string{kubevip.AllowReconcileWithoutEndpoints: "TRUE"}},
+			},
+			expected: true,
+		},
+		{
+			name: "cluster policy without opt-in",
+			service: &v1.Service{
+				Spec:       v1.ServiceSpec{ExternalTrafficPolicy: v1.ServiceExternalTrafficPolicyTypeCluster},
+				ObjectMeta: metav1.ObjectMeta{Annotations: map[string]string{}},
+			},
+			expected: false,
+		},
+		{
+			name: "local policy with opt-in",
+			service: &v1.Service{
+				Spec:       v1.ServiceSpec{ExternalTrafficPolicy: v1.ServiceExternalTrafficPolicyTypeLocal},
+				ObjectMeta: metav1.ObjectMeta{Annotations: map[string]string{kubevip.AllowReconcileWithoutEndpoints: "true"}},
+			},
+			expected: false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			actual := shouldAllowReconcileWithoutEndpoints(test.service)
+			if actual != test.expected {
+				t.Fatalf("expected %v, got %v", test.expected, actual)
+			}
+		})
+	}
+}

pkg/kubevip/annotations.go

@@ -68,6 +68,9 @@ const (
 	// Name of the service lease object
 	ServiceLease = "kube-vip.io/leaseName"
 
+	// Allow service reconciliation even when no endpoints are present (Cluster policy only)
+	AllowReconcileWithoutEndpoints = "kube-vip.io/allow-reconcile-without-endpoints"
+
 	// Enable DDNS for the service
 	ServiceDDNS = "kube-vip.io/ddns"