Enabling multicloud K8s communication with Skupper
Tags: docker, kubernetes, devops
Published: 2020-09-15 20:25:24

#Intro#

There are many challenges that engineering teams face when attempting to incorporate a multi-cloud approach into their infrastructure goals. Kubernetes does a good job of addressing some of these issues, but managing the communication of clusters that span multiple cloud providers in multiple regions can become a daunting task for teams. Often this requires complex VPNs and special firewall rules to multi-cloud cluster communication. 

In this post, I will be introducing you to Skupper, an open source project for enabling secure communication across Kubernetes cluster. Skupper allows your application to span multiple cloud providers, data centers, and regions. Let's see it in action!

#Getting Started#

This tutorial will demonstrate how to distribute the [Istio Bookinfo Application](https://istio.io/docs/examples/bookinfo/) microservices across multiple public and private clusters. The services require no coding changes to work in the distributed application environment. With Skupper, the application behaves as if all the services are running in the same cluster.

In this tutorial, you will deploy the *productpage* and ratings services on a remote, public cluster in namespace `aws-eu-west` and the details and reviews services in a local, on-premises cluster in namespace `laptop`.

###Overview###

**Figure 1 - Bookinfo service deployment**

![Alt Text](https://dev-to-uploads.s3.amazonaws.com/i/jjgiavry2arh129ven17.gif)

The image above shows how the services will be deployed.

* Each cluster runs two of the application services.
* An ingress route to the *productpage* service provides internet user access to the application.

If all services were installed on the public cluster, then the application would work as originally designed. However, since two of the services are on the *laptop* cluster, the application fails. *productpage* can not send requests to *details* or to *reviews*.

This demo will show how Skupper can solve the connectivity problem presented by this arrangement of service deployments.

**Figure 2 - Bookinfo service deployment with Skupper**

![Alt Text](https://dev-to-uploads.s3.amazonaws.com/i/gye0ijj7xuw9ckq8jzdq.gif)

Skupper is a distributed system with installations running in one or more clusters or namespaces. Connected Skupper installations share information about what services each installation exposes. Each Skupper installation learns which services are exposed on every other installation. Skupper then runs proxy service endpoints in each namespace to properly route requests to or from every exposed service.

* In the public namespace, the *details* and *reviews* proxies intercept requests for their services and forward them to the Skupper network.
* In the private namespace, the *details* and *reviews* proxies receive requests from the Skupper network and send them to the related service.
* In the private namespace, the *ratings* proxy intercepts requests for its service and forwards them to the Skupper network.
* In the public namespace, the *ratings* proxy receives requests from the Skupper network and sends them to the related service.

###Prerequisites###

To run this tutorial you will need:

* The `kubectl` command-line tool, version 1.15 or later [(installation guide)](https://kubernetes.io/docs/tasks/tools/install-kubectl/)
* The `skupper` command-line tool, the latest version [(installation guide)](https://skupper.io/start/index.html#step-1-install-the-skupper-command-line-tool-in-your-environment)
* Two Kubernetes namespaces, from any providers you choose, on any clusters you choose
* The yaml files from https://github.com/skupperproject/skupper-examples-bookinfo.git
* Two logged-in console terminals, one for each cluster or namespace

#Step 1: Deploy the Bookinfo application#

This step creates a service and a deployment for each of the four Bookinfo microservices.

Namespace `aws-eu-west`:

```
$ kubectl apply -f public-cloud.yaml
service/productpage created
deployment.extensions/productpage-v1 created
service/ratings created
deployment.extensions/ratings-v1 created
```

Namespace `laptop`:

```
$ kubectl apply -f private-cloud.yaml 
service/details created
deployment.extensions/details-v1 created
service/reviews created
deployment.extensions/reviews-v3 created
```

#Step 2: Expose the public productpage service#

Namespace `aws-eu-west`:

```
kubectl expose deployment/productpage-v1 --port 9080 --type LoadBalancer

```

The Bookinfo application is accessed from the public internet through this ingress port to the `productpage` service.

#Step 3: Observe that the application does not work#

The web address for the Bookinfo application can be discovered from namespace `aws-eu-west`:

```
$ echo $(kubectl get service/productpage -o jsonpath='http://{.status.loadBalancer.ingress[0].hostname}:9080')

```

Open the address in a web browser. *Productpage* responds but the page will show errors as services in namespace `laptop` are not reachable.

We can fix that now.

#Step 4: Set up Skupper#

This step initializes the Skupper environment on each cluster.
Namespace `laptop`:

```
skupper init
```

Namespace `aws-eu-west`:

```
skupper init
```

Now the Skupper infrastructure is running. Use `skupper status` in each console terminal to see that Skupper is available.

```
$ skupper status
Namespace '<ns>' is ready.  It is connected to 0 other namespaces.

```

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

#Step 5: Connect your Skupper installations#

Now you need to connect your namespaces with a Skupper connection.

This is a two step process.
The `skupper connection-token <file>` command directs Skupper to generate a secret token file with certificates that grant permission to other Skupper instances to connect to this Skupper's network.

Note: Protect this file as you would do for any file that holds login credentials.

The `skupper connect <file>` command directs Skupper to connect to another Skupper's network. This step completes the Skupper connection.

Note that in this arrangement the Skupper instances join to form peer networks. Typically the Skupper opening the network port will be on the public cluster. A cluster running on `laptop` may not even have an address that is reachable from the internet. After the connection is made, the Skupper network members are peers and it does not matter which Skupper opened the network port and which connected to it.

The console terminals in this demo are run by the same user on the same host. This makes the token file in the ${HOME} directory available to both terminals. If your terminals are on different machines then you may need to use `scp` or a similar tool to transfer the token file to the system hosting the `laptop` terminal.

###Generate a Skupper network connection token###

Namespace `aws-eu-west`:

```
skupper connection-token ${HOME}/PVT-to-PUB-connection-token.yaml

```

###Open a Skupper connection###

Namespace `laptop`:

```
skupper connect ${HOME}/PVT-to-PUB-connection-token.yaml
```

###Check the connection###

Namespace `aws-eu-west`:

```
$ skupper status
Skupper enabled for "aws-eu-west". It is connected to 1 other sites.

```

Namespace `laptop`:

```
$ skupper status
Skupper enabled for "laptop". It is connected to 1 other sites.

```

#Step 6: Virtualize the services you want shared#

You now have a Skupper network capable of multi-cluster communication but no services are associated with it. This step uses the `kubectl annotate` command to notify Skupper that a service is to be included in the Skupper network.

Skupper uses the annotation as the indication that a service must be virtualized. The service that receives the annotation is the physical target for network requests and the proxies that Skupper deploys in other namespaces are the virtual targets for network requests. The Skupper infrastructure then routes requests between the virtual services and the target service.

Namespace `aws-eu-west`:

```
$ kubectl annotate service ratings skupper.io/proxy=http
service/ratings annotated

```

Namespace `laptop`:

```
$ kubectl annotate service details skupper.io/proxy=http
service/details annotated

$ kubectl annotate service reviews skupper.io/proxy=http
service/reviews annotated

```

Skupper is now making the annotated services available to every namespace in the Skupper network. The Bookinfo application will work as the `productpage` service on the public cluster has access to the `details` and `reviews` services on the private cluster and as the reviews service on the private cluster has access to the ratings service on the public cluster.

#Step 7: Observe that the application works#

The web address for the Bookinfo app can be discovered from namespace `aws-eu-west`:

```
$ echo $(kubectl get service/productpage -o jsonpath='http://{.status.loadBalancer.ingress[0].hostname}:9080')

```

Open the address in a web browser. The application should now work with no errors.

#Clean up#

Skupper and the Bookinfo services may be removed from the clusters.

Namespace `aws-eu-west`:

```
skupper delete
kubectl delete -f public-cloud.yaml

```

Namespace `laptop`:

```
skupper delete
kubectl delete -f private-cloud.yaml 
```

#Final Thoughts#

Enabling a multi-cloud approach has a lot of benefits and is getting easier, thanks to tools like Skupper. If you have time, try some of  Skupper's other examples on its [Github Repo](https://github.com/skupperproject). I hope you learned something from this post. Stay tuned for more!