Accessing an FTP server using Skupper

Securely connect to an FTP server on a remote Kubernetes cluster

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: Install the Skupper command-line tool
• Step 2: Set up your namespaces
• Step 3: Deploy the FTP server
• Step 4: Create your sites
• Step 5: Link your sites
• Step 6: Expose the FTP server
• Step 7: Run the FTP client
• Cleaning up
• Summary
• Next steps
• About this example

Overview

This example shows you how you can use Skupper to connect an FTP client on one Kubernetes cluster to an FTP server on another.

It demonstrates use of Skupper with multi-port services such as FTP. It uses FTP in passive mode (which is more typical these days) and a restricted port range that simplifies Skupper configuration.

Prerequisites

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

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

Step 1: Install the Skupper command-line tool

This example uses the Skupper command-line tool to deploy Skupper. 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/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 2: Set up your namespaces

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

Your kubeconfig is stored in a file in your home directory. The skupper and kubectl commands use the KUBECONFIG environment variable to locate it.

A single kubeconfig supports only one active context per user. Since you will be using multiple contexts at once in this exercise, you need to create distinct kubeconfigs.

For each namespace, open a new terminal window. In each terminal, set the KUBECONFIG environment variable to a different path and log in to your cluster. Then create the namespace you wish to use and set the namespace on your current context.

Note: The login procedure varies by provider. See the documentation for yours:

• Minikube
• Amazon Elastic Kubernetes Service (EKS)
• Azure Kubernetes Service (AKS)
• Google Kubernetes Engine (GKE)
• IBM Kubernetes Service
• OpenShift

Public:

export KUBECONFIG=~/.kube/config-public
# Enter your provider-specific login command
kubectl create namespace public
kubectl config set-context --current --namespace public

Private:

export KUBECONFIG=~/.kube/config-private
# Enter your provider-specific login command
kubectl create namespace private
kubectl config set-context --current --namespace private

Step 3: Deploy the FTP server

In Private, use kubectl apply to deploy the FTP server.

Private:

kubectl apply -f server

Sample output:

$ kubectl apply -f server
deployment.apps/ftp-server created

Step 4: Create your sites

A Skupper site is a location where components of your application are running. Sites are linked together to form a network for your application. In Kubernetes, a site is associated with a namespace.

For each namespace, use skupper init to create a site. This deploys the Skupper router and controller. Then use skupper status to see the outcome.

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

Public:

skupper init
skupper status

Sample output:

$ skupper init
Waiting for LoadBalancer IP or hostname...
Waiting for status...
Skupper is now installed in namespace 'public'.  Use 'skupper status' to get more information.

$ skupper status
Skupper is enabled for namespace "public". It is not connected to any other sites. It has no exposed services.

Private:

skupper init
skupper status

Sample output:

$ skupper init
Waiting for LoadBalancer IP or hostname...
Waiting for status...
Skupper is now installed in namespace 'private'.  Use 'skupper status' to get more information.

$ skupper status
Skupper is enabled for namespace "private". It is not connected to any other sites. It has no exposed services.

As you move through the steps below, you can use skupper status at any time to check your progress.

Step 5: 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 use of two skupper commands in conjunction, skupper token create and skupper link create.

The skupper token create command generates a secret token that signifies permission to create a link. The token also carries the link details. Then, in a remote site, The skupper link create command uses the token to create a link to the site that generated it.

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 create in site Public to generate the token. Then, use skupper link create in site Private to link the sites.

Public:

skupper token create ~/secret.token

Sample output:

$ skupper token create ~/secret.token
Token written to ~/secret.token

Private:

skupper link create ~/secret.token

Sample output:

$ skupper link create ~/secret.token
Site configured to link to https://10.105.193.154:8081/ed9c37f6-d78a-11ec-a8c7-04421a4c5042 (name=link1)
Check the status of the link using 'skupper link status'.

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 creation.

Step 6: Expose the FTP server

In Private, use skupper expose to expose the FTP server on all linked sites.

Private:

skupper expose deployment/ftp-server --port 21100 --port 21

Sample output:

$ skupper expose deployment/ftp-server --port 21100 --port 21
deployment ftp-server exposed as ftp-server

Step 7: Run the FTP client

In Public, use kubectl run and the curl image to perform FTP put and get operations.

Public:

echo "Hello!" | kubectl run ftp-client --stdin --rm --image=docker.io/curlimages/curl --restart=Never -- -s -T - ftp://example:example@ftp-server/greeting
kubectl run ftp-client --attach --rm --image=docker.io/curlimages/curl --restart=Never -- -s ftp://example:example@ftp-server/greeting

Sample output:

$ echo "Hello!" | kubectl run ftp-client --stdin --rm --image=docker.io/curlimages/curl --restart=Never -- -s -T - ftp://example:example@ftp-server/greeting
pod "ftp-client" deleted

$ kubectl run ftp-client --attach --rm --image=docker.io/curlimages/curl --restart=Never -- -s ftp://example:example@ftp-server/greeting
Hello!
pod "ftp-client" deleted

Cleaning up

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

Public:

skupper delete

Private:

skupper delete
kubectl delete -f server

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.