feat: support externalname services

fixes #3505

Author: msvticket

pkg/backend/endpoint_resolver.go

@@ -3,6 +3,7 @@ package backend
 import (
 	"context"
 	"fmt"
+	"net"
 
 	awssdk "github.com/aws/aws-sdk-go/aws"
 	"github.com/go-logr/logr"
@@ -27,12 +28,17 @@ var ErrNotFound = errors.New("backend not found")
 type EndpointResolver interface {
 	// ResolvePodEndpoints will resolve endpoints backed by pods directly.
 	// returns resolved podEndpoints and whether there are unready endpoints that can potentially turn ready in future reconciles.
-	ResolvePodEndpoints(ctx context.Context, svcKey types.NamespacedName, port intstr.IntOrString,
-		opts ...EndpointResolveOption) ([]PodEndpoint, bool, error)
+	ResolvePodEndpoints(ctx context.Context, svckey types.NamespacedName, svc *corev1.Service, port intstr.IntOrString, opts ...EndpointResolveOption) ([]IpEndpoint, bool, error)
 
 	// ResolveNodePortEndpoints will resolve endpoints backed by nodePort.
 	ResolveNodePortEndpoints(ctx context.Context, svcKey types.NamespacedName, port intstr.IntOrString,
 		opts ...EndpointResolveOption) ([]NodePortEndpoint, error)
+
+	// FindService finds a k8s service
+	FindService(ctx context.Context, svcKey types.NamespacedName) (*corev1.Service, error)
+
+	// ResolveExternalNameEndpoints will resolve external name using dns
+	ResolveExternalNameEndpoints(ctx context.Context, svc *corev1.Service, port intstr.IntOrString) ([]IpEndpoint, error)
 }
 
 // NewDefaultEndpointResolver constructs new defaultEndpointResolver
@@ -42,6 +48,7 @@ func NewDefaultEndpointResolver(k8sClient client.Client, podInfoRepo k8s.PodInfo
 		podInfoRepo:          podInfoRepo,
 		failOpenEnabled:      failOpenEnabled,
 		endpointSliceEnabled: endpointSliceEnabled,
+		dnsResolver:          net.DefaultResolver,
 		logger:               logger,
 	}
 }
@@ -58,13 +65,34 @@ type defaultEndpointResolver struct {
 	// [Pod Endpoint] whether to use endpointSlice instead of endpoints
 	endpointSliceEnabled bool
 	logger               logr.Logger
+	// dnsResolver to use for resolving external names
+	dnsResolver dnsResolver
+}
+
+type dnsResolver interface {
+	LookupHost(ctx context.Context, host string) (addrs []string, err error)
+}
+
+func (r *defaultEndpointResolver) ResolveExternalNameEndpoints(ctx context.Context, svc *corev1.Service, port intstr.IntOrString) ([]IpEndpoint, error) {
+	if port.Type == intstr.String {
+		return nil, fmt.Errorf("port of target group must be numeric for external name")
+	}
+	addrs, err := r.dnsResolver.LookupHost(ctx, svc.Spec.ExternalName)
+	if err != nil {
+		return nil, err
+	}
+	endpoints := make([]IpEndpoint, len(addrs))
+	for i, ip := range addrs {
+		endpoints[i] = IpEndpoint{IP: ip, Port: int64(port.IntVal)}
+	}
+	return endpoints, nil
 }
 
-func (r *defaultEndpointResolver) ResolvePodEndpoints(ctx context.Context, svcKey types.NamespacedName, port intstr.IntOrString, opts ...EndpointResolveOption) ([]PodEndpoint, bool, error) {
+func (r *defaultEndpointResolver) ResolvePodEndpoints(ctx context.Context, svcKey types.NamespacedName, svc *corev1.Service, port intstr.IntOrString, opts ...EndpointResolveOption) ([]IpEndpoint, bool, error) {
 	resolveOpts := defaultEndpointResolveOptions()
 	resolveOpts.ApplyOptions(opts)
 
-	_, svcPort, err := r.findServiceAndServicePort(ctx, svcKey, port)
+	_, svcPort, err := r.findServicePort(svc, port)
 	if err != nil {
 		return nil, false, err
 	}
@@ -140,9 +168,9 @@ func (r *defaultEndpointResolver) computeServiceEndpointsData(ctx context.Contex
 	return endpointsDataList, nil
 }
 
-func (r *defaultEndpointResolver) resolvePodEndpointsWithEndpointsData(ctx context.Context, svcKey types.NamespacedName, svcPort corev1.ServicePort, endpointsDataList []EndpointsData, podReadinessGates []corev1.PodConditionType) ([]PodEndpoint, bool, error) {
-	var readyPodEndpoints []PodEndpoint
-	var unknownPodEndpoints []PodEndpoint
+func (r *defaultEndpointResolver) resolvePodEndpointsWithEndpointsData(ctx context.Context, svcKey types.NamespacedName, svcPort corev1.ServicePort, endpointsDataList []EndpointsData, podReadinessGates []corev1.PodConditionType) ([]IpEndpoint, bool, error) {
+	var readyPodEndpoints []IpEndpoint
+	var unknownPodEndpoints []IpEndpoint
 	containsPotentialReadyEndpoints := false
 
 	for _, epsData := range endpointsDataList {
@@ -170,7 +198,7 @@ func (r *defaultEndpointResolver) resolvePodEndpointsWithEndpointsData(ctx conte
 					containsPotentialReadyEndpoints = true
 					continue
 				}
-				podEndpoint := buildPodEndpoint(pod, epAddr, epPort)
+				podEndpoint := buildPodEndpoint(&pod, epAddr, epPort)
 				if ep.Conditions.Ready != nil && *ep.Conditions.Ready {
 					readyPodEndpoints = append(readyPodEndpoints, podEndpoint)
 					continue
@@ -214,13 +242,14 @@ func (r *defaultEndpointResolver) resolvePodEndpointsWithEndpointsData(ctx conte
 }
 
 func (r *defaultEndpointResolver) findServiceAndServicePort(ctx context.Context, svcKey types.NamespacedName, port intstr.IntOrString) (*corev1.Service, corev1.ServicePort, error) {
-	svc := &corev1.Service{}
-	if err := r.k8sClient.Get(ctx, svcKey, svc); err != nil {
-		if apierrors.IsNotFound(err) {
-			return nil, corev1.ServicePort{}, fmt.Errorf("%w: %v", ErrNotFound, err.Error())
-		}
+	svc, err := r.FindService(ctx, svcKey)
+	if err != nil {
 		return nil, corev1.ServicePort{}, err
 	}
+	return r.findServicePort(svc, port)
+}
+
+func (r *defaultEndpointResolver) findServicePort(svc *corev1.Service, port intstr.IntOrString) (*corev1.Service, corev1.ServicePort, error) {
 	svcPort, err := k8s.LookupServicePort(svc, port)
 	if err != nil {
 		return nil, corev1.ServicePort{}, fmt.Errorf("%w: %v", ErrNotFound, err.Error())
@@ -229,6 +258,17 @@ func (r *defaultEndpointResolver) findServiceAndServicePort(ctx context.Context,
 	return svc, svcPort, nil
 }
 
+func (r *defaultEndpointResolver) FindService(ctx context.Context, svcKey types.NamespacedName) (*corev1.Service, error) {
+	svc := &corev1.Service{}
+	if err := r.k8sClient.Get(ctx, svcKey, svc); err != nil {
+		if apierrors.IsNotFound(err) {
+			return nil, fmt.Errorf("%w: %v", ErrNotFound, err.Error())
+		}
+		return nil, err
+	}
+	return svc, nil
+}
+
 // filterNodesByReadyConditionStatus will filter out nodes that matches specified ready condition status
 func filterNodesByReadyConditionStatus(nodes []*corev1.Node, readyCondStatus corev1.ConditionStatus) []*corev1.Node {
 	var nodesWithMatchingReadyStatus []*corev1.Node
@@ -281,8 +321,8 @@ func buildEndpointsDataFromEndpointSliceList(epsList *discovery.EndpointSliceLis
 	return endpointsDataList
 }
 
-func buildPodEndpoint(pod k8s.PodInfo, epAddr string, port int32) PodEndpoint {
-	return PodEndpoint{
+func buildPodEndpoint(pod *k8s.PodInfo, epAddr string, port int32) IpEndpoint {
+	return IpEndpoint{
 		IP:   epAddr,
 		Port: int64(port),
 		Pod:  pod,