Skupper enables inter-cluster TCP communication

TCP tunneling with Skupper

This example is part of a suite of examples showing the different ways you can use Skupper to connect services across cloud providers, data centers, and edge sites.

Contents

• Overview
• Prerequisites
• Step 1: Access your Kubernetes clusters
• Step 2: Create your Kubernetes namespaces
• Step 3: Install Skupper on your Kubernetes clusters
• Step 4: Install the Skupper command-line tool
• Step 5: Deploy the TCP echo server
• Step 6: Create your sites
• Step 7: Link your sites
• Step 8: Expose the TCP echo service
• Step 9: Access the public service remotely
• Cleaning up
• Summary
• Next steps
• About this example

Overview

This is a simple demonstration of TCP communication tunneled through a Skupper network from a private to a public cluster and back again. During development of this demonstration, the private cluster was running locally, while the public cluster was on AWS.

We set up a Skupper network between the two clusters, start a TCP echo-server on the public cluster, then communicate to it from the private cluster and receive its replies. At no time is any port opened on the machine running the private cluster.

Prerequisites

• Access to at least one Kubernetes cluster, from any provider you choose.

• The kubectl command-line tool, version 1.15 or later (installation guide).

Step 1: Access your Kubernetes clusters

Skupper is designed for use with multiple Kubernetes clusters. The skupper and kubectl commands use your kubeconfig and current context to select the cluster and namespace where they operate.

This example uses multiple cluster contexts at once. The KUBECONFIG environment variable tells skupper and kubectl which kubeconfig to use.

For each cluster, open a new terminal window. In each terminal, set the KUBECONFIG environment variable to a different path and log in to your cluster.

Public:

export KUBECONFIG=/tmp/public-kubeconfig
<provider-specific login command>

Private:

export KUBECONFIG=/tmp/private-kubeconfig
<provider-specific login command>

Note: The login procedure varies by provider.

Step 2: Create your Kubernetes namespaces

The example application has different components deployed to different Kubernetes namespaces. To set up our example, we need to create the namespaces.

For each cluster, use kubectl create namespace and kubectl config set-context to create the namespace you wish to use and set the namespace on your current context.

Public:

kubectl create namespace public
kubectl config set-context --current --namespace public

Private:

kubectl create namespace private
kubectl config set-context --current --namespace private

Step 3: Install Skupper on your Kubernetes clusters

Using Skupper on Kubernetes requires the installation of the Skupper custom resource definitions (CRDs) and the Skupper controller.

For each cluster, use kubectl apply with the Skupper installation YAML to install the CRDs and controller.

Public:

kubectl apply -f https://skupper.io/v2/install.yaml

Private:

kubectl apply -f https://skupper.io/v2/install.yaml

Step 4: Install the Skupper command-line tool

This example uses the Skupper command-line tool to create Skupper resources. You need to install the skupper command only once for each development environment.

On Linux or Mac, you can use the install script (inspect it here) to download and extract the command:

curl https://skupper.io/v2/install.sh | sh

The script installs the command under your home directory. It prompts you to add the command to your path if necessary.

For Windows and other installation options, see Installing Skupper.

Step 5: Deploy the TCP echo server

Public:

kubectl apply -f ./public-deployment.yaml

Step 6: Create your sites

A Skupper site is a location where your application workloads are running. Sites are linked together to form a network for your application.

For each namespace, use skupper site create with a site name of your choice. This creates the site resource and deploys the Skupper router to the namespace.

Note: If you are using Minikube, you need to start minikube tunnel before you run skupper site create.

Public:

skupper site create public --enable-link-access

Sample output:

$ skupper site create public --enable-link-access
Waiting for status...
Site "public" is configured. Check the status to see when it is ready

Private:

skupper site create private

Sample output:

$ skupper site create private
Waiting for status...
Site "private" is configured. Check the status to see when it is ready

You can use skupper site status at any time to check the status of your site.

Step 7: Link your sites

A Skupper link is a channel for communication between two sites. Links serve as a transport for application connections and requests.

Creating a link requires the use of two Skupper commands in conjunction: skupper token issue and skupper token redeem. The skupper token issue command generates a secret token that can be transferred to a remote site and redeemed for a link to the issuing site. The skupper token redeem command uses the token to create the link.

Note: The link token is truly a secret. Anyone who has the token can link to your site. Make sure that only those you trust have access to it.

First, use skupper token issue in Public to generate the token. Then, use skupper token redeem in Private to link the sites.

Public:

skupper token issue ~/secret.token

Sample output:

$ skupper token issue ~/secret.token
Waiting for token status ...

Grant "west-cad4f72d-2917-49b9-ab66-cdaca4d6cf9c" is ready
Token file /run/user/1000/skewer/secret.token created

Transfer this file to a remote site. At the remote site,
create a link to this site using the "skupper token redeem" command:

	skupper token redeem <file>

The token expires after 1 use(s) or after 15m0s.

Private:

skupper token redeem ~/secret.token

Sample output:

$ skupper token redeem ~/secret.token
Waiting for token status ...
Token "west-cad4f72d-2917-49b9-ab66-cdaca4d6cf9c" has been redeemed
You can now safely delete /run/user/1000/skewer/secret.token

If your terminal sessions are on different machines, you may need to use scp or a similar tool to transfer the token securely. By default, tokens expire after a single use or 15 minutes after being issued.

Step 8: Expose the TCP echo service

Create a listener in the private cluster where the client runs and a connector in the public cluster where the echo server runs. This makes the public echo service reachable inside the private namespace as tcp-go-echo on port 9090.

Private:

skupper listener create tcp-go-echo 9090

Public:

skupper connector create tcp-go-echo 9090 --workload deployment/tcp-go-echo

Step 9: Access the public service remotely

From the private cluster, forward traffic to the exposed echo service and verify that it responds.

Private:

kubectl get svc
kubectl port-forward service/tcp-go-echo 9090:9090
telnet 0.0.0.0 9090

Sample output:

$ telnet 0.0.0.0 9090
hello, Skupper
tcp-go-echo-7ddbc7756c-wxgcq : HELLO, SKUPPER

Cleaning up

To remove Skupper and the other resources from this exercise, use the following commands.

Public:

skupper site delete --all
kubectl delete -f ./public-deployment.yaml

Private:

skupper site delete --all

Summary

The TCP echo server runs only in the public cluster, but Skupper exposes it as a local service in the private cluster. By forwarding to the private cluster, you can reach the public service without opening any ports on the private side. Skupper handles the encrypted traffic between clusters transparently, so the echo replies arrive as if the service were running locally.

Next steps

Check out the other examples on the Skupper website.

About this example

This example was produced using Skewer, a library for documenting and testing Skupper examples.

Skewer provides utility functions for generating the README and running the example steps. Use the ./plano command in the project root to see what is available.

To quickly stand up the example using Minikube, try the ./plano demo command.