feat(adminapi): support specification of http/https via appProtocol on the admin port

CHANGELOG.md

@@ -108,6 +108,8 @@ Adding a new version? You'll need three changes:
   in translating and applying configurations to Kong.
   [#5296](https://github.com/Kong/kubernetes-ingress-controller/pull/5296)
   [#5299](https://github.com/Kong/kubernetes-ingress-controller/pull/5299)
+- Added support in Gateway Discovery for specifying that the Admin API should use HTTP via the appProtocol field on the admin port. 
+  [#5251](https://github.com/Kong/kubernetes-ingress-controller/pull/5251)
 
 ### Fixed
 

internal/adminapi/endpoints.go

@@ -162,15 +162,19 @@ func adminAPIFromEndpoint(
 		Namespace: endpoint.TargetRef.Namespace,
 	}
 
+	// Format for calling the Admin API. If the port explicitly indicates http as the AppProtocol, use http.
+	// Otherwise, default to HTTPS as a best practice. Consumers may want to use HTTP if they have a service mesh in place which
+	// is already handling TLS authentication for them.
+	adminAPIAddressFormat := "https://%s:%d"
+	if port.AppProtocol != nil && *port.AppProtocol == "http" {
+		adminAPIAddressFormat = "http://%s:%d"
+	}
+
 	// NOTE: Endpoint's addresses are assumed to be fungible, therefore we pick
 	// only the first one.
 	// For the context please see the `Endpoint.Addresses` godoc.
 	eAddress := endpoint.Addresses[0]
 
-	// NOTE: We assume https below because the referenced Admin API
-	// server will live in another Pod/elsewhere so allowing http would
-	// not be considered best practice.
-
 	switch dnsStrategy {
 	case cfgtypes.ServiceScopedPodDNSStrategy:
 		if service.Name == "" {
@@ -184,7 +188,7 @@ func adminAPIFromEndpoint(
 		address := fmt.Sprintf("%s.%s.%s.svc", ipAddr, service.Name, service.Namespace)
 
 		return DiscoveredAdminAPI{
-			Address: fmt.Sprintf("https://%s:%d", address, *port.Port),
+			Address: fmt.Sprintf(adminAPIAddressFormat, address, *port.Port),
 			PodRef:  podNN,
 		}, nil
 
@@ -193,7 +197,7 @@ func adminAPIFromEndpoint(
 		address := fmt.Sprintf("%s.%s.pod", ipAddr, service.Namespace)
 
 		return DiscoveredAdminAPI{
-			Address: fmt.Sprintf("https://%s:%d", address, *port.Port),
+			Address: fmt.Sprintf(adminAPIAddressFormat, address, *port.Port),
 			PodRef:  podNN,
 		}, nil
 
@@ -203,7 +207,7 @@ func adminAPIFromEndpoint(
 			bounded = fmt.Sprintf("[%s]", bounded)
 		}
 		return DiscoveredAdminAPI{
-			Address: fmt.Sprintf("https://%s:%d", bounded, *port.Port),
+			Address: fmt.Sprintf(adminAPIAddressFormat, bounded, *port.Port),
 			PodRef:  podNN,
 		}, nil
 

internal/adminapi/endpoints_test.go

@@ -81,6 +81,34 @@ func TestDiscoverer_AddressesFromEndpointSlice(t *testing.T) {
 			),
 			dnsStrategy: cfgtypes.NamespaceScopedPodDNSStrategy,
 		},
+		{
+			name: "basic with appProtocol http",
+			endpoints: discoveryv1.EndpointSlice{
+				ObjectMeta:  endpointsSliceObjectMeta,
+				AddressType: discoveryv1.AddressTypeIPv4,
+				Endpoints: []discoveryv1.Endpoint{
+					{
+						Addresses: []string{"10.0.0.1", "10.0.0.2"},
+						Conditions: discoveryv1.EndpointConditions{
+							Ready:       lo.ToPtr(true),
+							Terminating: lo.ToPtr(false),
+						},
+						TargetRef: testPodReference(namespaceName, "pod-1"),
+					},
+				},
+				Ports: builder.NewEndpointPort(8444).WithName("admin").WithAppProtocol("http").IntoSlice(),
+			},
+			portNames: sets.New("admin"),
+			want: sets.New(
+				DiscoveredAdminAPI{
+					Address: "http://10-0-0-1.ns.pod:8444",
+					PodRef: k8stypes.NamespacedName{
+						Name: "pod-1", Namespace: namespaceName,
+					},
+				},
+			),
+			dnsStrategy: cfgtypes.NamespaceScopedPodDNSStrategy,
+		},
 		{
 			name: "basic",
 			endpoints: discoveryv1.EndpointSlice{

internal/util/builder/endpointport.go

@@ -32,6 +32,12 @@ func (b *EndpointPortBuilder) WithName(name string) *EndpointPortBuilder {
 	return b
 }
 
+// WithAppProtocol sets the appProtocol on the endpoint port.
+func (b *EndpointPortBuilder) WithAppProtocol(appProtocol string) *EndpointPortBuilder {
+	b.ep.AppProtocol = lo.ToPtr(appProtocol)
+	return b
+}
+
 // Build returns the configured EndpointPort.
 func (b *EndpointPortBuilder) Build() discoveryv1.EndpointPort {
 	return b.ep