Don't write out dummy zone hints in clusters with no zones

If you set `trafficDistribution: PreferClose` on a service in a
cluster with no defined zones, then it would add

  hints:
    forZones:
    - name: ""

to each endpoint. This ended up working anyway since kube-proxy would
likewise end up looking for an endpoint for the "" zone, but it's
unnecessary, since you'd get exactly the same behavior by just leaving
all of the endpoints unhinted. (Of course there's no point in using
PreferClose traffic distribution in this case, but this will make
PreferSameNode cleaner.)

staging/src/k8s.io/endpointslice/trafficdist/trafficdist.go

@@ -115,13 +115,19 @@ func (preferCloseHeuristic) needsUpdate(slice *discoveryv1.EndpointSlice) bool {
 		if !endpointReady(endpoint) {
 			continue
 		}
-		var zone string
-		if endpoint.Zone != nil {
-			zone = *endpoint.Zone
-		}
 
-		if endpoint.Hints == nil || len(endpoint.Hints.ForZones) != 1 || endpoint.Hints.ForZones[0].Name != zone {
+		if endpoint.Zone != nil {
-			return true
+			// We want a zone hint.
+			if endpoint.Hints == nil || len(endpoint.Hints.ForZones) != 1 || endpoint.Hints.ForZones[0].Name != *endpoint.Zone {
+				// ...but either it's missing or it's incorrect
+				return true
+			}
+		} else {
+			// We don't want a zone hint.
+			if endpoint.Hints != nil && len(endpoint.Hints.ForZones) > 0 {
+				// ...but we have a stale hint.
+				return true
+			}
 		}
 	}
 	return false
@@ -134,10 +140,17 @@ func (preferCloseHeuristic) update(slice *discoveryv1.EndpointSlice) {
 			continue
 		}
 
-		var zone string
+		var forZones []discoveryv1.ForZone
 		if endpoint.Zone != nil {
-			zone = *endpoint.Zone
+			forZones = []discoveryv1.ForZone{{Name: *endpoint.Zone}}
+		}
+
+		if forZones != nil {
+			slice.Endpoints[i].Hints = &discoveryv1.EndpointHints{
+				ForZones: forZones,
+			}
+		} else {
+			slice.Endpoints[i].Hints = nil
 		}
-		slice.Endpoints[i].Hints = &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: zone}}}
 	}
 }

staging/src/k8s.io/endpointslice/trafficdist/trafficdist_test.go

@@ -264,6 +264,131 @@ func TestReconcileHints(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "should not create zone hints if there are no zones",
+
+			trafficDistribution: ptr.To(corev1.ServiceTrafficDistributionPreferClose),
+			slicesToCreate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							NodeName:   ptr.To("node-1"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.2"},
+							NodeName:   ptr.To("node-2"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							NodeName:   ptr.To("node-3"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.4"},
+							NodeName:   ptr.To("node-4"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			slicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							NodeName:   ptr.To("node-5"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.6"},
+							NodeName:   ptr.To("node-6"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.7"},
+							NodeName:   ptr.To("node-7"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.8"},
+							NodeName:   ptr.To("node-8"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			wantSlicesToCreate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							NodeName:   ptr.To("node-1"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.2"},
+							NodeName:   ptr.To("node-2"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							NodeName:   ptr.To("node-3"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.4"},
+							NodeName:   ptr.To("node-4"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			wantSlicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							NodeName:   ptr.To("node-5"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.6"},
+							NodeName:   ptr.To("node-6"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.7"},
+							NodeName:   ptr.To("node-7"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.8"},
+							NodeName:   ptr.To("node-8"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+		},
 		{
 			name: "unready endpoints should not trigger updates",