Use consistent protocol determination

docs/content/routing/providers/kubernetes-crd.md

@@ -313,6 +313,16 @@ Register the `IngressRoute` kind in the Kubernetes cluster before creating `Ingr
       tls.key: LS0tLS1CRUdJTiBQUklWQVRFIEtFWS0tLS0tCi0tLS0tRU5EIFBSSVZBVEUgS0VZLS0tLS0=
     ```
 
+!!! important "Configuring Backend Protocol"
+
+    There are 3 ways to configure the backend protocol for communication between Traefik and your pods:
+	
+    - Setting the scheme explicitly (http/https/h2c)
+    - Configuring the name of the kubernetes service port to start with https (https)
+    - Setting the kubernetes service port to use port 443 (https)
+
+    If you do not configure the above, Traefik will assume an http connection.
+
 ### Kind: `Middleware`
 
 `Middleware` is the CRD implementation of a [Traefik middleware](../../middlewares/overview.md).

pkg/provider/kubernetes/crd/kubernetes_http.go

@@ -307,9 +307,9 @@ func (c configBuilder) loadServers(fallbackNamespace string, svc v1alpha1.LoadBa
 
 	var servers []dynamic.Server
 	if service.Spec.Type == corev1.ServiceTypeExternalName {
-		protocol := "http"
-		if portSpec.Port == 443 || strings.HasPrefix(portSpec.Name, "https") {
-			protocol = "https"
+		protocol, err := parseServiceProtocol(svc.Scheme, portSpec.Name, portSpec.Port)
+		if err != nil {
+			return nil, err
 		}
 
 		return append(servers, dynamic.Server{
@@ -341,17 +341,9 @@ func (c configBuilder) loadServers(fallbackNamespace string, svc v1alpha1.LoadBa
 			return nil, fmt.Errorf("cannot define a port for %s/%s", namespace, sanitizedName)
 		}
 
-		protocol := httpProtocol
-		scheme := svc.Scheme
-		switch scheme {
-		case httpProtocol, httpsProtocol, "h2c":
-			protocol = scheme
-		case "":
-			if portSpec.Port == 443 || strings.HasPrefix(portSpec.Name, httpsProtocol) {
-				protocol = httpsProtocol
-			}
-		default:
-			return nil, fmt.Errorf("invalid scheme %q specified", scheme)
+		protocol, err := parseServiceProtocol(svc.Scheme, portSpec.Name, portSpec.Port)
+		if err != nil {
+			return nil, err
 		}
 
 		for _, addr := range subset.Addresses {
@@ -448,3 +440,19 @@ func getTLSHTTP(ctx context.Context, ingressRoute *v1alpha1.IngressRoute, k8sCli
 
 	return nil
 }
+
+// parseServiceProtocol parses the scheme, port name, and number to determine the correct protocol.
+// an error is returned if the scheme provided is invalid.
+func parseServiceProtocol(providedScheme string, portName string, portNumber int32) (string, error) {
+	switch providedScheme {
+	case httpProtocol, httpsProtocol, "h2c":
+		return providedScheme, nil
+	case "":
+		if portNumber == 443 || strings.HasPrefix(portName, httpsProtocol) {
+			return httpsProtocol, nil
+		}
+		return httpProtocol, nil
+	}
+
+	return "", fmt.Errorf("invalid scheme %q specified", providedScheme)
+}

pkg/provider/kubernetes/crd/kubernetes_test.go

@@ -2311,3 +2311,72 @@ func TestLoadIngressRoutes(t *testing.T) {
 		})
 	}
 }
+
+func TestParseServiceProtocol(t *testing.T) {
+	testCases := []struct {
+		desc          string
+		scheme        string
+		portName      string
+		portNumber    int32
+		expected      string
+		expectedError bool
+	}{
+		{
+			desc:       "Empty scheme and name",
+			scheme:     "",
+			portName:   "",
+			portNumber: 1000,
+			expected:   "http",
+		},
+		{
+			desc:       "h2c scheme and emptyname",
+			scheme:     "h2c",
+			portName:   "",
+			portNumber: 1000,
+			expected:   "h2c",
+		},
+		{
+			desc:          "invalid scheme",
+			scheme:        "foo",
+			portName:      "",
+			portNumber:    1000,
+			expectedError: true,
+		},
+		{
+			desc:       "Empty scheme and https name",
+			scheme:     "",
+			portName:   "https-secure",
+			portNumber: 1000,
+			expected:   "https",
+		},
+		{
+			desc:       "Empty scheme and port number",
+			scheme:     "",
+			portName:   "",
+			portNumber: 443,
+			expected:   "https",
+		},
+		{
+			desc:       "https scheme",
+			scheme:     "https",
+			portName:   "",
+			portNumber: 1000,
+			expected:   "https",
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			protocol, err := parseServiceProtocol(test.scheme, test.portName, test.portNumber)
+			if test.expectedError {
+				assert.Error(t, err)
+			} else {
+				assert.Equal(t, test.expected, protocol)
+			}
+		})
+	}
+}