Kubernetes Gateway API Controller for SSH Tunneling

Disclaimer

This should be considered alpha quality and not ready for production use.

Overview

This Kubernetes Gateway API controller enables exposing Kubernetes services through SSH tunnels. It works with any SSH tunneling provider that supports reverse port forwarding, including:

• Pico.sh - A premium SSH tunneling service with automatic TLS
• Serveo - A free SSH tunneling service
• Plain OpenSSH servers - Any SSH server with reverse port forwarding enabled

How it works

The controller establishes SSH connections to external SSH servers and creates reverse port forwards (SSH -R flag) to expose Kubernetes services. When Gateway API resources are created, the controller:

1. Establishes SSH connections to the configured SSH server
2. Creates reverse port forwards for each listener
3. Routes traffic from the SSH server back to Kubernetes services

Client Browser
    |
    V
your-service.ssh-provider.com (DNS to SSH provider)
    |
    V
SSH Reverse Tunnel (controller Pod)
    |
    V
your-service.default.svc.cluster.local:80 (ClusterIP Service)
    |
    V
Pods selected by your service

Supported SSH Providers

Pico.sh

Pico.sh is a premium SSH tunneling service that provides:

• Automatic TLS termination
• Custom domains
• Multi-region support
• Per-site analytics

Configuration:

env:
- name: SSH_SERVER
  value: "tuns.sh:22"
- name: SSH_USERNAME
  value: "your-pico-username"
- name: GATEWAY_CONTROLLER_NAME
  value: "tunnels.pico.sh/gateway-api-controller"

Usage:

# Your services will be available at:
# https://your-username-service-name.tuns.sh
# or https://your-username-service-name.nue.tuns.sh (region-specific)

Serveo

Serveo is a free SSH tunneling service.

Configuration:

env:
- name: SSH_SERVER
  value: "serveo.net:22"
- name: SSH_USERNAME
  value: "your-serveo-username"
- name: GATEWAY_CONTROLLER_NAME
  value: "tunnels.serveo.net/gateway-api-controller"

Usage:

# Your services will be available at:
# https://your-service-name.serveo.net

Plain OpenSSH Server

You can use any SSH server with reverse port forwarding enabled.

Configuration:

env:
- name: SSH_SERVER
  value: "your-ssh-server.com:22"
- name: SSH_USERNAME
  value: "your-ssh-username"
- name: GATEWAY_CONTROLLER_NAME
  value: "tunnels.ssh.gateway-api-controller"

SSH Server Requirements:

• AllowTcpForwarding yes in sshd_config
• GatewayPorts yes in sshd_config (for binding to all interfaces)
• User must have permission to bind to ports

Installation

1. Build the controller container

The controller is not available on any upstream docker registry. You need to build the image and upload it in a registry accessible by your Kubernetes cluster.

cd gateway-api/gateway-controller
docker build . -t ssh-gateway-api-controller:latest
docker tag ssh-gateway-api-controller:latest my-docker-registry.home.me:5001/ssh-gateway-api-controller:latest
docker push my-docker-registry.home.me:5001/ssh-gateway-api-controller

2. Configure the Kubernetes manifests

Edit gateway-api/k8s/combined.yaml and provide:

• The name of the Docker image containing the controller (built above, including the registry)
• Your SSH private key (base64-encoded)
• SSH server configuration

For instance, use this to encode your SSH key:

base64 -w0 < $HOME/.ssh/id_rsa

WARNING: Your SSH key cannot be protected by password.

3. Deploy the controller

The following must be run as a Kubernetes administrator:

kubectl apply -f gateway-api/k8s/combined.yaml

Verify that everything is working:

❯ kubectl get pods -o wide -n ssh-gateway-system
NAME                                       READY   STATUS    RESTARTS   AGE   IP             NODE     NOMINATED NODE   READINESS GATES
ssh-gateway-api-controller-5976f8677-ggclc   1/1     Running   0          23h     10.50.228.107   k8s-w1   <none>           <none>

❯ kubectl get gatewayclass
NAME                 CONTROLLER                                       ACCEPTED   AGE
ssh-gateway-cl   tunnels.ssh.gateway-api-controller   True       10d

❯ kubectl logs -f -n ssh-gateway-system ssh-gateway-api-controller-5976f8677-ggclc
time=2025-05-07T20:25:14.718Z level=INFO msg="starting manager"

Usage Examples

Example Application

Run the following as any user, in any namespace where you have permission to create deployments, services, and gateways:

kubectl apply -f example-apps/gateway-api/combined.yaml

This creates:

• A TCP echo server deployment
• A service exposing the echo server
• A Gateway with HTTP and TCP listeners
• HTTPRoute and TCPRoute resources

Verify the deployment

❯ kubectl get httproutes.gateway.networking.k8s.io
NAME              HOSTNAMES   AGE
http-echo-route               77s

❯ kubectl get tcproutes.gateway.networking.k8s.io
NAME             AGE
tcp-echo-route   82s

❯ kubectl get pods -o wide
NAME                               READY   STATUS    RESTARTS   AGE     IP              NODE     NOMINATED NODE   READINESS GATES
tcp-echo-server-7cbfdb4c5f-hdmkc   1/1     Running   0          16s     10.50.46.52     k8s-w2   <none>           <none>

Access your services

Depending on your SSH provider, your services will be available at:

Pico.sh:

curl https://your-username-web-test.tuns.sh
nc your-username-web-test.tuns.sh 59123

Serveo:

curl https://web-test.serveo.net
nc web-test.serveo.net 59123

Custom SSH server:

curl http://your-ssh-server.com:80
nc your-ssh-server.com 59123

Configuration

Environment Variables

The controller can be configured using the following environment variables:

Variable	Default	Description
SSH_SERVER	localhost:22	SSH server address and port
SSH_USERNAME	tunnel-user	SSH username
SSH_PRIVATE_KEY_PATH	/ssh/id	Path to SSH private key
GATEWAY_CONTROLLER_NAME	tunnels.ssh.gateway-api-controller	Controller name for GatewayClass matching
CONNECT_TIMEOUT	5s	SSH connection timeout
KEEP_ALIVE_INTERVAL	10s	SSH keepalive interval
BACKOFF_INTERVAL	5s	Reconnection backoff interval

SSH Key Requirements

• Must be a private key (RSA, DSA, ECDSA, or Ed25519)
• Cannot be password-protected
• Must be stored as a Kubernetes Secret
• Must have appropriate permissions (0400)

Gateway API Resources

The controller supports the following Gateway API resources:

• GatewayClass: Defines the controller responsible for managing Gateways
• Gateway: Defines listeners (ports and protocols) for incoming traffic
• HTTPRoute: Routes HTTP traffic to backend services
• TCPRoute: Routes TCP traffic to backend services

Troubleshooting

Common Issues

1. SSH Connection Failed

   • Verify SSH server address and port
   • Check SSH key format and permissions
   • Ensure SSH server allows reverse port forwarding

2. Gateway Not Accepted

   • Verify GatewayClass controller name matches
   • Check GatewayClass is accepted

3. Routes Not Working

   • Verify backend services are running
   • Check service selectors and ports
   • Ensure SSH tunnels are established

Debugging

Enable debug logging by setting the log level:

env:
- name: LOG_LEVEL
  value: "debug"

Check controller logs:

kubectl logs -f -n ssh-gateway-system ssh-gateway-api-controller-xxx

Clean up

Demo app:

kubectl delete -f example-apps/gateway-api/combined.yaml

Controller:

kubectl delete -f gateway-api/k8s/combined.yaml

License

Copyright 2025 Davide Guerri

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.

NOTICE: This project was created by Davide Guerri. Modifications must retain attribution.