Backend TLS

Originate a one-way TLS connection from the Gateway to a backend.

About one-way TLS

When you configure a TLS listener on your Gateway, the Gateway typically terminates incoming TLS traffic and forwards the unencrypted traffic to the backend service. However, you might have a service that only accepts TLS connections, or you want to forward traffic a secured Backend service that is external to the cluster.

You can use the Kubernetes Gateway API BackendTLSPolicy to configure TLS origination from the Gateway to a service in the cluster. This policy supports simple, one-way TLS use cases.

However, to additionally set up different hostnames on the Backend that you want to route to via SNI, or to originate TLS connections to an external backend, use the kgateway BackendConfigPolicy instead.

About this guide

In this guide, you learn how to use the BackendTLSPolicy and BackendConfigPolicy resources originate one-way TLS connections for the following services:

• In-cluster service: An NGINX server that is configured with a self-signed TLS certificate and deployed to the same cluster as the Gateway. You use a BackendTLSPolicy to originate TLS connections to NGINX.
• External service: The httpbin.org hostname, which represents an external service that you want to originate a TLS connection to. You use a BackendConfigPolicy resource to originate TLS connections to that hostname.

Before you begin

1. Follow the Get started guide to install kgateway.

2. Follow the Sample app guide to create a gateway proxy with an HTTP listener and deploy the httpbin sample app.

3. Get the external address of the gateway and save it in an environment variable.

   Cloud Provider LoadBalancerPort-forward for local testing

   export INGRESS_GW_ADDRESS=$(kubectl get svc -n kgateway-system http -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
   echo $INGRESS_GW_ADDRESS  

   kubectl port-forward deployment/http -n kgateway-system 8080:8080

4. Important: Install the experimental channel of the Kubernetes Gateway API to use this feature.

   kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.3.0/experimental-install.yaml

In-cluster service

Deploy an NGINX server in your cluster that is configured for TLS traffic. Then, instruct the gateway proxy to terminate TLS traffic at the gateway and originate a new TLS connection from the gateway proxy to the NGINX server.

Deploy the sample app

The following example uses an NGINX server with a self-signed TLS certificate. For the configuration, see the test directory in the kgateway GitHub repository.

1. Deploy the NGINX server with a self-signed TLS certificate.

   kubectl apply -f https://raw.githubusercontent.com/kgateway-dev/kgateway/refs/heads/main/test/kubernetes/e2e/features/backendtls/testdata/nginx.yaml

2. Verify that the NGINX server is running.

   kubectl get pods -l app.kubernetes.io/name=nginx

   Example output:

   NAME    READY   STATUS    RESTARTS   AGE
   nginx   1/1     Running   0          9s

Create a TLS policy

Create a TLS policy for the NGINX workload. You can use the Gateway API BackendTLSPolicy for simple, one-way TLS connections. For more advanced TLS connections or simply to reduce the number of resources if you use other backend connections, create a BackendConfigPolicy instead.

Create an HTTPRoute

Create an HTTPRoute that routes traffic to the NGINX server on the example.com hostname and HTTPS port 8443. Note that the parent Gateway is the sample http Gateway resource that you created before you began.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: nginx-route
  labels:
    app: nginx
spec:
  parentRefs:
  - name: http
    namespace: kgateway-system
  hostnames:
  - "example.com"
  rules:
  - backendRefs:
    - name: nginx
      port: 8443
EOF

Verify the TLS connection

Now that your TLS backend and routing resources are configured, verify the TLS connection.

1. Send a request to the NGINX server and verify that you get back a 200 HTTP response code.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:8080/ -H "host: example.com:8080"

   curl -vi http://localhost:8080/ -H "host: example.com:8080"

   Example output:

   * Host localhost:8080 was resolved.
   * IPv6: ::1
   * IPv4: 127.0.0.1
   *   Trying [::1]:8080...
   * Connected to localhost (::1) port 8080
   > GET / HTTP/1.1
   > Host: example.com:8080
   > User-Agent: curl/8.7.1
   > Accept: */*
   > 
   * Request completely sent off
   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK

2. Enable port-forwarding on the Gateway.

   kubectl port-forward deploy/http -n kgateway-system 19000

3. In your browser, open the Envoy stats page at http://127.0.0.1:19000/stats.

4. Search for the following stats that indicate the TLS connection is working. The count increases each time that the Gateway sends a request to the NGINX server.

   • cluster.kube_default_nginx_8443.ssl.versions.TLSv1.2: The number of TLSv1.2 connections from the Envoy gateway proxy to the NGINX server.
   • cluster.kube_default_nginx_8443.ssl.handshake: The number of successful TLS handshakes between the Envoy gateway proxy and the NGINX server.

External service

Set up a Backend resource that represents your external service. Then, use a BackendTLSPolicy to instruct the gateway proxy to originate a TLS connection from the gateway proxy to the external service.

1. Create a Backend resource that represents your external service. In this example, you use a static Backend that routes traffic to the httpbin.org site. Make sure to include the HTTPS port 443 so that traffic is routed to this port.

   kubectl apply -f- <<EOF
   apiVersion: gateway.kgateway.dev/v1alpha1
   kind: Backend
   metadata:
     name: httpbin-org
     namespace: default
   spec:
     type: Static
     static:
       hosts:
       - host: httpbin.org
         port: 443
   EOF

2. Create a TLS policy that originates a TLS connection to the Backend that you created in the previous step. To originate the TLS connection, you use known trusted CA certificates. You can use the Gateway API BackendTLSPolicy for simple, one-way TLS connections. For more advanced TLS connections or simply to reduce the number of resources if you use other backend connections, create a BackendConfigPolicy instead. Note that the BackendConfigPolicy is only supported for Envoy-based kgateway proxies. For agentgateway proxies, use the BackendTLSPolicy.

   BackendConfigPolicyBackendTLSPolicy

   The steps in this section use the Envoy-based kgateway proxy. The steps do not work with the agentgateway proxy.

   kubectl apply -f- <<EOF
   apiVersion: gateway.kgateway.dev/v1alpha1
   kind: BackendConfigPolicy
   metadata:
     name: httpbin-org
     namespace: default
   spec:
     targetRefs:
       - name: httpbin-org
         kind: Backend
         group: gateway.kgateway.dev
     tls:
       sni: httpbin.org
       wellKnownCACertificates: System
   EOF

   Note that to use the BackendTLSPolicy, you must have the experimental channel of the Kubernetes Gateway API version 1.4 or later.

   kubectl apply -f- <<EOF
   apiVersion: gateway.networking.k8s.io/v1
   kind: BackendTLSPolicy
   metadata:
     name: httpbin-org
     namespace: default
   spec:
     targetRefs:
       - name: httpbin-org
         kind: Backend
         group: gateway.kgateway.dev
     validation:
       hostname: httpbin.org
       wellKnownCACertificates: System
   EOF

3. Create an HTTPRoute that rewrites traffic on the httpbin-external.example domain to the httpbin.org hostname and routes traffic to your Backend.

   kubectl apply -f- <<EOF
   apiVersion: gateway.networking.k8s.io/v1
   kind: HTTPRoute
   metadata:
     name: httpbin-org
     namespace: default
   spec:
     parentRefs:
     - name: http
       namespace: kgateway-system
     hostnames:
     - "httpbin-external.example"
     rules:
       - matches:
         - path:
             type: PathPrefix
             value: /anything
         backendRefs:
         - name: httpbin-org
           kind: Backend
           group: gateway.kgateway.dev
         filters:
         - type: URLRewrite
           urlRewrite:
             hostname: httpbin.org
   EOF

4. Send a request to the httpbin-external.example domain. Verify that the host is rewritten to https://httpbin.org/anything and that you get back a 200 HTTP response code.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:8080/anything -H "host: httpbin-external.example" 

   curl -vi http://localhost:8080/anything -H "host: httpbin-external.example" 

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   {
     "args": {}, 
     "data": "", 
     "files": {}, 
     "form": {}, 
     "headers": {
       "Accept": "*/*", 
       "Host": "httpbin.org", 
       "User-Agent": "curl/8.7.1", 
       "X-Amzn-Trace-Id": "Root=1-6881126a-03bfc90450805b9703e66e78", 
       "X-Envoy-Expected-Rq-Timeout-Ms": "15000", 
       "X-Envoy-External-Address": "10.0.15.215"
     }, 
     "json": null, 
     "method": "GET", 
     "origin": "10.0.X.XXX, 3.XXX.XXX.XXX", 
     "url": "https://httpbin.org/anything"
   }
   

Cleanup

In-cluster service

External service

Delete the resources that you created.

kubectl delete httproute httpbin-org
kubectl delete backendconfigpolicy httpbin-org
kubectl delete backend httpbin-org

kubectl delete httproute httpbin-org
kubectl delete backendtlspolicy httpbin-org
kubectl delete backend httpbin-org