Use a SOCKS5 Proxy to Access the Kubernetes API

FEATURE STATE: Kubernetes v1.24 [stable]

This page shows how to use a SOCKS5 proxy to access the API of a remote Kubernetes cluster. This is useful when the cluster you want to access does not expose its API directly on the public internet.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

Your Kubernetes server must be version v1.24. To check the version, enter kubectl version.

You need SSH client software (the ssh tool), and an SSH service running on the remote server. You must be able to log in to the SSH service on the remote server.

Task context

Figure 1 represents what you're going to achieve in this task.

  • You have a client computer, referred to as local in the steps ahead, from where you're going to create requests to talk to the Kubernetes API.
  • The Kubernetes server/API is hosted on a remote server.
  • You will use SSH client and server software to create a secure SOCKS5 tunnel between the local and the remote server. The HTTPS traffic between the client and the Kubernetes API will flow over the SOCKS5 tunnel, which is itself tunnelled over SSH.

graph LR; subgraph local[Local client machine] client([client])-- local
traffic .-> local_ssh[Local SSH
SOCKS5 proxy]; end local_ssh[SSH
proxy]-- SSH Tunnel -->sshd subgraph remote[Remote server] sshd[SSH
server]-- local traffic -->service1; end client([client])-. proxied HTTPs traffic
going through the proxy .->service1[Kubernetes API]; classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000; classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff; classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5; class ingress,service1,service2,pod1,pod2,pod3,pod4 k8s; class client plain; class cluster cluster;
Figure 1. SOCKS5 tutorial components

Using ssh to create a SOCKS5 proxy

This command starts a SOCKS5 proxy between your client machine and the remote server. The SOCKS5 proxy lets you connect to your cluster's API server.

# The SSH tunnel continues running in the foreground after you run this
ssh -D 1080 -q -N username@kubernetes-remote-server.example
  • -D 1080: opens a SOCKS proxy on local port :1080.
  • -q: quiet mode. Causes most warning and diagnostic messages to be suppressed.
  • -N: Do not execute a remote command. Useful for just forwarding ports.
  • username@kubernetes-remote-server.example: the remote SSH server where the Kubernetes cluster is running.

Client configuration

To explore the Kubernetes API you'll first need to instruct your clients to send their queries through the SOCKS5 proxy we created earlier.

For command-line tools, set the https_proxy environment variable and pass it to commands that you run.

export https_proxy=socks5h://localhost:1080

When you set the https_proxy variable, tools such as curl route HTTPS traffic through the proxy you configured. For this to work, the tool must support SOCKS5 proxying.

curl -k -v https://localhost/api

To use the official Kubernetes client kubectl with a proxy, set the proxy-url element for the relevant cluster entry within your ~/.kube/config file. For example:

apiVersion: v1
- cluster:
    certificate-authority-data: LRMEMMW2 # shortened for readability 
    server: https://localhost            # the "Kubernetes API" in the diagram above
    proxy-url: socks5://localhost:1080   # the "SSH SOCKS5 proxy" in the diagram above (DNS resolution over socks is built-in)
  name: default
- context:
    cluster: default
    user: default
  name: default
current-context: default
kind: Config
preferences: {}
- name: default
    client-certificate-data: LS0tLS1CR== # shortened for readability
    client-key-data: LS0tLS1CRUdJT=      # shortened for readability

If the tunnel is operating and you use kubectl with a context that uses this cluster, you can interact with your cluster through that proxy. For example:

kubectl get pods
NAMESPACE     NAME                                     READY   STATUS      RESTARTS   AGE
kube-system   coredns-85cb69466-klwq8                  1/1     Running     0          5m46s

Clean up

Stop the ssh port-forwarding process by pressing CTRL+C on the terminal where it is running.

Type unset https_proxy in a terminal to stop forwarding http traffic through the proxy.

Further reading

Last modified May 03, 2022 at 6:46 PM PST: follow-up to pr 31527 to address comments (0bdd4d2d03)