cmd/k8s-operator: fix DNS reconciler for dual-stack clusters (#13057)

* cmd/k8s-operator: fix DNS reconciler for dual-stack clusters

This fixes a bug where DNS reconciler logic was always assuming
that no more than one EndpointSlice exists for a Service.
In fact, there can be multiple, for example, in dual-stack
clusters, but also in other cases this is valid (as per kube docs).
This PR:
- allows for multiple EndpointSlices
- picks out the ones for IPv4 family
- deduplicates addresses

Updates tailscale/tailscale#13056

Signed-off-by: Irbe Krumina <irbe@tailscale.com>
Co-authored-by: Tom Proctor <tomhjp@users.noreply.github.com>

cmd/k8s-operator/dnsrecords.go

@@ -24,6 +24,7 @@ import (
 	operatorutils "tailscale.com/k8s-operator"
 	tsapi "tailscale.com/k8s-operator/apis/v1alpha1"
 	"tailscale.com/util/mak"
+	"tailscale.com/util/set"
 )
 
 const (
@@ -167,36 +168,49 @@ func (dnsRR *dnsRecordsReconciler) maybeProvision(ctx context.Context, headlessS
 		}
 	}
 
-	// Get the Pod IP addresses for the proxy from the EndpointSlice for the
+	// Get the Pod IP addresses for the proxy from the EndpointSlices for
-	// headless Service.
+	// the headless Service. The Service can have multiple EndpointSlices
+	// associated with it, for example in dual-stack clusters.
 	labels := map[string]string{discoveryv1.LabelServiceName: headlessSvc.Name} // https://kubernetes.io/docs/concepts/services-networking/endpoint-slices/#ownership
-	eps, err := getSingleObject[discoveryv1.EndpointSlice](ctx, dnsRR.Client, dnsRR.tsNamespace, labels)
+	var eps = new(discoveryv1.EndpointSliceList)
-	if err != nil {
+	if err := dnsRR.List(ctx, eps, client.InNamespace(dnsRR.tsNamespace), client.MatchingLabels(labels)); err != nil {
-		return fmt.Errorf("error getting the EndpointSlice for the proxy's headless Service: %w", err)
+		return fmt.Errorf("error listing EndpointSlices for the proxy's headless Service: %w", err)
 	}
-	if eps == nil {
+	if len(eps.Items) == 0 {
 		logger.Debugf("proxy's headless Service EndpointSlice does not yet exist. We will reconcile again once it's created")
 		return nil
 	}
-	// An EndpointSlice for a Service can have a list of endpoints that each
+	// Each EndpointSlice for a Service can have a list of endpoints that each
 	// can have multiple addresses - these are the IP addresses of any Pods
 	// selected by that Service. Pick all the IPv4 addresses.
-	ips := make([]string, 0)
+	// It is also possible that multiple EndpointSlices have overlapping addresses.
-	for _, ep := range eps.Endpoints {
+	// https://kubernetes.io/docs/concepts/services-networking/endpoint-slices/#duplicate-endpoints
+	ips := make(set.Set[string], 0)
+	for _, slice := range eps.Items {
+		if slice.AddressType != discoveryv1.AddressTypeIPv4 {
+			logger.Infof("EndpointSlice is for AddressType %s, currently only IPv4 address type is supported", slice.AddressType)
+			continue
+		}
+		for _, ep := range slice.Endpoints {
+			if !epIsReady(&ep) {
+				logger.Debugf("Endpoint with addresses %v appears not ready to receive traffic %v", ep.Addresses, ep.Conditions.String())
+				continue
+			}
 			for _, ip := range ep.Addresses {
 				if !net.IsIPv4String(ip) {
 					logger.Infof("EndpointSlice contains IP address %q that is not IPv4, ignoring. Currently only IPv4 is supported", ip)
 				} else {
-				ips = append(ips, ip)
+					ips.Add(ip)
+				}
 			}
 		}
 	}
-	if len(ips) == 0 {
+	if ips.Len() == 0 {
 		logger.Debugf("EndpointSlice for the Service contains no IPv4 addresses. We will reconcile again once they are created.")
 		return nil
 	}
 	updateFunc := func(rec *operatorutils.Records) {
-		mak.Set(&rec.IP4, fqdn, ips)
+		mak.Set(&rec.IP4, fqdn, ips.Slice())
 	}
 	if err = dnsRR.updateDNSConfig(ctx, updateFunc); err != nil {
 		return fmt.Errorf("error updating DNS records: %w", err)
@@ -204,6 +218,17 @@ func (dnsRR *dnsRecordsReconciler) maybeProvision(ctx context.Context, headlessS
 	return nil
 }
 
+// epIsReady reports whether the endpoint is currently in a state to receive new
+// traffic. As per kube docs, only explicitly set 'false' for 'Ready' or
+// 'Serving' conditions or explicitly set 'true' for 'Terminating' condition
+// means that the Endpoint is NOT ready.
+// https://github.com/kubernetes/kubernetes/blob/60c4c2b2521fb454ce69dee737e3eb91a25e0535/pkg/apis/discovery/types.go#L109-L131
+func epIsReady(ep *discoveryv1.Endpoint) bool {
+	return (ep.Conditions.Ready == nil || *ep.Conditions.Ready) &&
+		(ep.Conditions.Serving == nil || *ep.Conditions.Serving) &&
+		(ep.Conditions.Terminating == nil || !*ep.Conditions.Terminating)
+}
+
 // maybeCleanup ensures that the DNS record for the proxy has been removed from
 // dnsrecords ConfigMap and the tailscale.com/dns-records-reconciler finalizer
 // has been removed from the Service. If the record is not found in the

cmd/k8s-operator/dnsrecords_test.go

@@ -8,6 +8,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -87,13 +88,16 @@ func TestDNSRecordsReconciler(t *testing.T) {
 		},
 	}
 	headlessForEgressSvcFQDN := headlessSvcForParent(egressSvcFQDN, "svc") // create the proxy headless Service
-	ep := endpointSliceForService(headlessForEgressSvcFQDN, "10.9.8.7")
+	ep := endpointSliceForService(headlessForEgressSvcFQDN, "10.9.8.7", discoveryv1.AddressTypeIPv4)
+	epv6 := endpointSliceForService(headlessForEgressSvcFQDN, "2600:1900:4011:161:0:d:0:d", discoveryv1.AddressTypeIPv6)
+
 	mustCreate(t, fc, egressSvcFQDN)
 	mustCreate(t, fc, headlessForEgressSvcFQDN)
 	mustCreate(t, fc, ep)
+	mustCreate(t, fc, epv6)
 	expectReconciled(t, dnsRR, "tailscale", "egress-fqdn") // dns-records-reconciler reconcile the headless Service
 	// ConfigMap should now have a record for foo.bar.ts.net -> 10.8.8.7
-	wantHosts := map[string][]string{"foo.bar.ts.net": {"10.9.8.7"}}
+	wantHosts := map[string][]string{"foo.bar.ts.net": {"10.9.8.7"}} // IPv6 endpoint is currently ignored
 	expectHostsRecords(t, fc, wantHosts)
 
 	// 2. DNS record is updated if tailscale.com/tailnet-fqdn annotation's
@@ -106,7 +110,7 @@ func TestDNSRecordsReconciler(t *testing.T) {
 	expectHostsRecords(t, fc, wantHosts)
 
 	// 3. DNS record is updated if the IP address of the proxy Pod changes.
-	ep = endpointSliceForService(headlessForEgressSvcFQDN, "10.6.5.4")
+	ep = endpointSliceForService(headlessForEgressSvcFQDN, "10.6.5.4", discoveryv1.AddressTypeIPv4)
 	mustUpdate(t, fc, ep.Namespace, ep.Name, func(ep *discoveryv1.EndpointSlice) {
 		ep.Endpoints[0].Addresses = []string{"10.6.5.4"}
 	})
@@ -116,7 +120,7 @@ func TestDNSRecordsReconciler(t *testing.T) {
 
 	// 4. DNS record is created for an ingress proxy configured via Ingress
 	headlessForIngress := headlessSvcForParent(ing, "ingress")
-	ep = endpointSliceForService(headlessForIngress, "10.9.8.7")
+	ep = endpointSliceForService(headlessForIngress, "10.9.8.7", discoveryv1.AddressTypeIPv4)
 	mustCreate(t, fc, headlessForIngress)
 	mustCreate(t, fc, ep)
 	expectReconciled(t, dnsRR, "tailscale", "ts-ingress") // dns-records-reconciler should reconcile the headless Service
@@ -140,6 +144,17 @@ func TestDNSRecordsReconciler(t *testing.T) {
 	expectReconciled(t, dnsRR, "tailscale", "ts-ingress")
 	wantHosts["another.ingress.ts.net"] = []string{"7.8.9.10"}
 	expectHostsRecords(t, fc, wantHosts)
+
+	// 7. A not-ready Endpoint is removed from DNS config.
+	mustUpdate(t, fc, ep.Namespace, ep.Name, func(ep *discoveryv1.EndpointSlice) {
+		ep.Endpoints[0].Conditions.Ready = ptr.To(false)
+		ep.Endpoints = append(ep.Endpoints, discoveryv1.Endpoint{
+			Addresses: []string{"1.2.3.4"},
+		})
+	})
+	expectReconciled(t, dnsRR, "tailscale", "ts-ingress")
+	wantHosts["another.ingress.ts.net"] = []string{"1.2.3.4"}
+	expectHostsRecords(t, fc, wantHosts)
 }
 
 func headlessSvcForParent(o client.Object, typ string) *corev1.Service {
@@ -162,15 +177,21 @@ func headlessSvcForParent(o client.Object, typ string) *corev1.Service {
 	}
 }
 
-func endpointSliceForService(svc *corev1.Service, ip string) *discoveryv1.EndpointSlice {
+func endpointSliceForService(svc *corev1.Service, ip string, fam discoveryv1.AddressType) *discoveryv1.EndpointSlice {
 	return &discoveryv1.EndpointSlice{
 		ObjectMeta: metav1.ObjectMeta{
-			Name:      svc.Name,
+			Name:      fmt.Sprintf("%s-%s", svc.Name, string(fam)),
 			Namespace: svc.Namespace,
 			Labels:    map[string]string{discoveryv1.LabelServiceName: svc.Name},
 		},
+		AddressType: fam,
 		Endpoints: []discoveryv1.Endpoint{{
 			Addresses: []string{ip},
+			Conditions: discoveryv1.EndpointConditions{
+				Ready:       ptr.To(true),
+				Serving:     ptr.To(true),
+				Terminating: ptr.To(false),
+			},
 		}},
 	}
 }