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Exposing a TCP Service

Overview

This guide walks through creating TCP routing configuration for Kong Gateway in Kubernetes using either the TCPIngress custom resource or TCPRoute and TLSRoute Gateway APIs resource.

TCP-based Ingress means that Kong Gateway simply forwards the TCP stream to a Pod of a Service that’s running inside Kubernetes. Kong Gateway will not perform any sort of transformations.

There are two modes available:

• Port based routing: In this mode, Kong Gateway simply proxies all traffic it receives on a specific port to the Kubernetes Service. TCP connections are load balanced across all the available pods of the Service.
• SNI based routing: In this mode, Kong Gateway accepts a TLS-encrypted stream at the specified port and can route traffic to different services based on the SNI present in the TLS handshake. Kong Gateway will also terminate the TLS handshake and forward the TCP stream to the Kubernetes Service.

Installation

Please follow the deployment documentation to install the Kubernetes Ingress Controller onto your Kubernetes cluster.

Installing the Gateway APIs

If you wish to use the Gateway APIs examples, follow the supplemental Gateway APIs installation instructions.

Testing connectivity to Kong Gateway

This guide assumes that PROXY_IP environment variable is set to contain the IP address or URL pointing to Kong Gateway. If you’ve not done so, follow one of the deployment guides to configure this environment variable.

If everything is setup correctly, making a request to Kong Gateway should return back a HTTP 404 Not Found status code:

curl -i $PROXY_IP

Response:

HTTP/1.1 404 Not Found
Content-Type: application/json; charset=utf-8
Connection: keep-alive
Content-Length: 48
X-Kong-Response-Latency: 0
Server: kong/3.0.0

{"message":"no Route matched with those values"}

This is expected since Kong Gateway doesn’t know how to proxy the request yet.

Create a configuration group

Ingress and Gateway APIs controllers need a configuration that indicates which set of routing configuration they should recognize. This allows multiple controllers to coexist in the same cluster. Before creating individual routes, you need to create a class configuration to associate routes with:

echo "
apiVersion: networking.k8s.io/v1
kind: IngressClass
metadata:
  name: kong
spec:
  controller: ingress-controllers.konghq.com/kong
" | kubectl apply -f -

ingressclass.networking.k8s.io/kong configured

echo "
---
apiVersion: gateway.networking.k8s.io/v1beta1
kind: GatewayClass
metadata:
  name: kong
  annotations:
    konghq.com/gatewayclass-unmanaged: 'true'

spec:
  controllerName: konghq.com/kic-gateway-controller
---
apiVersion: gateway.networking.k8s.io/v1beta1
kind: Gateway
metadata:
  name: kong
spec:
  gatewayClassName: kong
  listeners:
  - name: proxy
    port: 80
    protocol: HTTP
  - name: proxy-ssl
    port: 443
    protocol: HTTPS
" | kubectl apply -f -

gatewayclass.gateway.networking.k8s.io/kong created
gateway.gateway.networking.k8s.io/kong created

kubectl get gateway kong

NAME   CLASS   ADDRESS        READY   AGE
kong   kong    203.0.113.42   True    4m46s

Kubernetes Ingress Controller recognizes the kong IngressClass and konghq.com/kic-gateway-controller GatewayClass by default. Setting the CONTROLLER_INGRESS_CLASS or CONTROLLER_GATEWAY_API_CONTROLLER_NAME environment variable to another value overrides these defaults.

Add TLS configuration

The routing configuration can include a certificate to present when clients connect over HTTPS. This is not required, as Kong Gateway will serve a default certificate if it cannot find another, but including TLS configuration along with routing configuration is typical.

First, create a test certificate for the tls9443.kong.example hostname using one of the following commands:

openssl req -subj '/CN=tls9443.kong.example' -new -newkey rsa:2048 -sha256 \
  -days 365 -nodes -x509 -keyout server.key -out server.crt \
  -addext "subjectAltName = DNS:tls9443.kong.example" \
  -addext "keyUsage = digitalSignature" \
  -addext "extendedKeyUsage = serverAuth" 2> /dev/null;
  openssl x509 -in server.crt -subject -noout

subject=CN = tls9443.kong.example

openssl req -subj '/CN=tls9443.kong.example' -new -newkey rsa:2048 -sha256 \
  -days 365 -nodes -x509 -keyout server.key -out server.crt \
  -extensions EXT -config <( \
   printf "[dn]\nCN=tls9443.kong.example\n[req]\ndistinguished_name = dn\n[EXT]\nsubjectAltName=DNS:tls9443.kong.example\nkeyUsage=digitalSignature\nextendedKeyUsage=serverAuth") 2>/dev/null;
  openssl x509 -in server.crt -subject -noout

subject=CN = tls9443.kong.example

Then, create a Secret containing the certificate:

kubectl create secret tls tls9443.kong.example --cert=./server.crt --key=./server.key

Response:

secret/tls9443.kong.example created

Adding TCP listens

Kong Gateway does not include any TCP listen configuration by default. To expose TCP listens, update the Deployment’s environment variables and port configuration:

kubectl patch deploy -n kong ingress-kong --patch '{
  "spec": {
    "template": {
      "spec": {
        "containers": [
          {
            "name": "proxy",
            "env": [
              {
                "name": "KONG_STREAM_LISTEN",
                "value": "0.0.0.0:9000, 0.0.0.0:9443 ssl"
              }
            ],
            "ports": [
              {
                "containerPort": 9000,
                "name": "stream9000",
                "protocol": "TCP"
              },
              {
                "containerPort": 9443,
                "name": "stream9443",
                "protocol": "TCP"
              }
            ]
          }
        ]
      }
    }
  }
}'

Response:

deployment.extensions/ingress-kong patched

The ssl parameter after the 9443 listen instructs Kong Gateway to expect TLS-encrypted TCP traffic on that port. The 9000 listen has no parameters, and expects plain TCP traffic.

Update the proxy Service

The proxy Service also needs to indicate the new ports:

kubectl patch service -n kong kong-proxy --patch '{
  "spec": {
    "ports": [
      {
        "name": "stream9000",
        "port": 9000,
        "protocol": "TCP",
        "targetPort": 9000
      },
      {
        "name": "stream9443",
        "port": 9443,
        "protocol": "TCP",
        "targetPort": 9443
      }
    ]
  }
}'

Response:

service/kong-proxy patched

Update the Gateway

If you are using the Gateway APIs (TCPRoute) option, your Gateway needs additional configuration under listeners. If you are using TCPIngress, skip this step.

kubectl patch --type=json gateway kong -p='[
    {
        "op":"add",
        "path":"/spec/listeners/-",
        "value":{
            "name":"stream9000",
            "port":9000,
            "protocol":"TCP"
        }
    },
    {
        "op":"add",
        "path":"/spec/listeners/-",
        "value":{
            "name":"stream9443",
            "port":9443,
            "protocol":"TLS",
            "hostname":"tls9443.kong.example",
			"tls": {
                "certificateRefs":[{
                    "group":"",
                    "kind":"Secret",
                    "name":"tls9443.kong.example"
                }]
			}
        }
    }
]'

Response:

gateway.gateway.networking.k8s.io/kong patched

Install TCP echo service

Next, install an example TCP service:

kubectl apply -f https://docs.konghq.com/assets/kubernetes-ingress-controller/examples/tcp-echo-service.yaml

Response:

deployment.apps/tcp-echo created
service/tcp-echo created

Route TCP traffic by port

To expose the service to the outside world, create the following TCPIngress resource:

echo "apiVersion: configuration.konghq.com/v1beta1
kind: TCPIngress
metadata:
  name: echo-plaintext
  annotations:
    kubernetes.io/ingress.class: kong
spec:
  rules:
  - port: 9000
    backend:
      serviceName: tcp-echo
      servicePort: 2701
" | kubectl apply -f -

tcpingress.configuration.konghq.com/echo-plaintext created

echo "apiVersion: gateway.networking.k8s.io/v1alpha2
kind: TCPRoute
metadata:
  name: echo-plaintext
spec:
  parentRefs:
  - name: kong
  rules:
  - backendRefs:
    - name: tcp-echo
      port: 9000
" | kubectl apply -f -

tcproute.gateway.networking.k8s.io/echo-plaintext created

This configuration instructs Kong Gateway to forward all traffic it receives on port 9000 to tcp-echo service on port 2701.

Test the configuration

Status will populate with an IP or Accepted condition once the route is ready:

kubectl get tcpingress

NAME             ADDRESS        AGE
echo-plaintext   <PROXY_IP>   3m18s

kubectl get tcproute echo-plaintext -ojsonpath='{.status.parents[0].conditions[?(@.reason=="Accepted")]}'

{"lastTransitionTime":"2022-11-14T19:48:51Z","message":"","observedGeneration":2,"reason":"Accepted","status":"True","type":"Accepted"}

Connect to this service using telnet:

$ telnet $PROXY_IP 9000
Trying 35.247.39.83...
Connected to 35.247.39.83.
Escape character is '^]'.
Welcome, you are connected to node gke-harry-k8s-dev-pool-1-e9ebab5e-c4gw.
Running on Pod tcp-echo-844545646c-gvmkd.
In namespace default.
With IP address 10.60.1.17.
This text will be echoed back.
This text will be echoed back.
^]
telnet> Connection closed.

We can see here that the tcp-echo service is now available outside the Kubernetes cluster via Kong Gateway.

Route TLS traffic by SNI

Next, we will demonstrate how Kong Gateway can route TLS-encrypted traffic to the tcp-echo service.

Create the following TCPIngress resource:

echo "apiVersion: configuration.konghq.com/v1beta1
kind: TCPIngress
metadata:
  name: echo-tls
  annotations:
    kubernetes.io/ingress.class: kong
spec:
  tls:
  - hosts:
    - tls9443.kong.example
    secretName: tls9443.kong.example
  rules:
  - host: tls9443.kong.example
    port: 9443
    backend:
      serviceName: tcp-echo
      servicePort: 2701
" | kubectl apply -f -

tcpingress.configuration.konghq.com/echo-tls created

echo "apiVersion: gateway.networking.k8s.io/v1alpha2
kind: TLSRoute
metadata:
  name: tlsecho
spec:
  parentRefs:
  - name: kong
  hostnames:
  - tls9443.kong.example
  rules:
  - backendRefs:
    - name: tcp-echo
      port: 9443
" | kubectl apply -f -

Test the configuration

You can now access the tcp-echo service on port 9443 with SNI tls9443.kong.example.

In real-world usage, you would create a DNS record for tls9443.kong.example pointing to your proxy Service’s public IP address, which causes TLS clients to add SNI automatically. For this demo, you’ll add it manually using the OpenSSL CLI:

echo "hello" | openssl s_client -connect $PROXY_IP:9443 -servername tls9443.kong.example -quiet 2>/dev/null 

Press Ctrl+C to exit after. Response:

Welcome, you are connected to node kind-control-plane.
Running on Pod tcp-echo-5f44d4c6f9-krnhk.
In namespace default.
With IP address 10.244.0.26.
hello