feat: add kgateway mcp app protocol to service port (#117)

Support using the kgateway mcp app protocol by default which can be
disabled by setting the following environment variable on the kmcp
controller deployment
```
      - env:
        - name: DISABLE_KGATEWAY_MCP_APP_PROTOCOL
          value: true
```

---------

Signed-off-by: JM Huibonhoa <jm.huibonhoa@solo.io>

Author: jmhbh

pkg/controller/transportadapter/transportadapter_translator.go

@@ -26,11 +26,13 @@ import (
 const (
 	transportAdapterRepository     = "ghcr.io/agentgateway/agentgateway"
 	defaultTransportAdapterVersion = "0.9.0"
+	kgatewayMcpAppProtocol         = "kgateway.dev/mcp"
 )
 
 // versionRegex validates that version strings contain only allowed characters
 // (alphanumeric, dots, hyphens) to prevent potential image injection attacks
 var versionRegex = regexp.MustCompile(`^[a-zA-Z0-9.\-]+$`)
+var disableKgatewayMcpAppProtocol = os.Getenv("DISABLE_KGATEWAY_MCP_APP_PROTOCOL")
 
 // Translator is the interface for translating MCPServer objects to TransportAdapter objects.
 type Translator interface {
@@ -481,6 +483,11 @@ func (t *transportAdapterTranslator) translateTransportAdapterService(
 	if port == 0 {
 		return nil, fmt.Errorf("deployment port must be specified for MCPServer %s", server.Name)
 	}
+
+	appProtocol := makePtr(kgatewayMcpAppProtocol)
+	if disableKgatewayMcpAppProtocol == "true" {
+		appProtocol = nil
+	}
 	service := &corev1.Service{
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      server.Name,
@@ -498,6 +505,7 @@ func (t *transportAdapterTranslator) translateTransportAdapterService(
 				TargetPort: intstr.IntOrString{
 					IntVal: int32(port),
 				},
+				AppProtocol: appProtocol,
 			}},
 			Selector: map[string]string{
 				"app.kubernetes.io/name":     server.Name,
@@ -663,3 +671,7 @@ func getTransportAdapterImage() string {
 
 	return fmt.Sprintf("%s:%s-musl", transportAdapterRepository, transportAdapterVersion)
 }
+
+func makePtr[T any](v T) *T {
+	return &v
+}

test/e2e/e2e_test.go

@@ -268,6 +268,7 @@ var _ = ginkgo.Describe("Manager", ginkgo.Ordered, func() {
 				g.Expect(service).NotTo(gomega.BeNil())
 				g.Expect(service.Spec.Ports).To(gomega.HaveLen(1))
 				g.Expect(service.Spec.Ports[0].Port).To(gomega.Equal(int32(3000)))
+				g.Expect(service.Spec.Ports[0].AppProtocol).To(gomega.HaveValue(gomega.Equal("kgateway.dev/mcp")))
 			}).Should(gomega.Succeed())
 
 			ginkgo.By("verifying that environment variables are loaded via envFrom")