Intro to vcluster: A Hands-on Tutorial

What is vcluster?

vcluster is an open source tool for creating and managing virtual Kubernetes clusters. A virtual cluster lives inside a namespace on a host cluster, but it appears to the user as if it’s a full-blown, standalone Kubernetes cluster. Think of it as a Kubernetes control plane in a namespace.

In this tutorial, we’ll look at how to get started using vcluster, some use cases for virtual clusters, and resources to learn more.

vcluster Series

Why vcluster?

Sharing Kubernetes clusters is hard. If you want multiple individuals or teams to use the same cluster, it can be painful to set up and maintain. But giving all of those people or teams their own clusters is also hard to manage and can be very expensive. vcluster lets you share clusters while letting users feel like they have their own cluster. Virtual clusters are also very quick to provision and destroy, so they’re even great for things like local development.

Requirements

For this tutorial, you will need the following:

1. Install the vcluster CLI

If you’re on a Mac and using Homebrew, you can install the vcluster CLI with this command:

brew install vcluster

For other platforms, see the installation instructions.

2. Create a virtual cluster

Run this command with the vcluster CLI:

vcluster create my-vcluster

This will create a virtual cluster and a namespace for it. As you can see, creating virtual clusters is super fast.

Next, let’s list the namespaces in the virtual cluster. When you run vcluster create the vcluster CLI automatically switches your kube context to point at the virtual cluster. So you can just run kubectl like you normally would.

kubectl get namespaces

Your output should look like this:

NAME              STATUS   AGE
default           Active   83s
kube-system       Active   83s
kube-public       Active   83s
kube-node-lease   Active   83s

Note that we don’t see any other namespaces that exist in the host cluster. We’re connected to the API server for the virtual cluster, so we will only see namespaces that have been created inside of it.

3. Create an Nginx deployment

Let’s create a namespace and an Nginx deployment inside the virtual cluster.

kubectl create namespace nginx
kubectl create deployment nginx --image=nginx -n nginx -r 2

This creates the deployment in the nginx namespace with two Nginx pods. We can then view the pods with kubectl.

kubectl get pods -n nginx

You should see two nginx pods in the Running state.

NAME                    READY   STATUS    RESTARTS   AGE
nginx-76d6c9b8c-j62h7   1/1     Running   0          8s
nginx-76d6c9b8c-57xk5   1/1     Running   0          8s

If the pods are in the ContainerCreating state, continue to run the get pods command until they come up.

4. Examine the host cluster

Now that our deployment is running, let’s disconnect from the virtual cluster and look at what’s happening under the hood in the host cluster.

vcluster disconnect

This automatically switches our kube context back to the previous one, the one for the host cluster. Let’s look at the namespaces there in the host cluster.

kubectl get namespaces

You will see the default Kubernetes namespaces and any others you created, plus a newer namespace called vcluster-my-vcluster. The virtual cluster is running inside that namespace. By default, vcluster prepends the string vcluster- to the name of the virtual cluster, but you can choose a different name for the namespace if you’d like by passing the -n flag to vcluster create.

Now let’s look at what’s running inside the namespace for the virtual cluster.

kubectl get pods -n vcluster-my-vcluster

Your output should look something like this:

NAME                                                   READY   STATUS    RESTARTS   AGE
coredns-56d44fc4b4-zrqjf-x-kube-system-x-my-vcluster   1/1     Running   0          17m
my-vcluster-0                                          2/2     Running   0          17m
nginx-76d6c9b8c-57xk5-x-nginx-x-my-vcluster            1/1     Running   0          12m
nginx-76d6c9b8c-j62h7-x-nginx-x-my-vcluster            1/1     Running   0          12m

Four pods are running in this example. The vcluster pod, which contains the virtual cluster’s API server and some additional tools, is called my-vcluster-0. There’s also a CoreDNS pod, which vcluster uses, and our two Nginx pods.

Notice that this time the pods names are much longer than when we viewed them from inside the virtual cluster. Here’s where we get into a big part of what makes vcluster work, the syncer.

The virtual cluster doesn’t contain a scheduler. Instead, the vcluster syncer process tells the underlying cluster to schedule workloads. This syncer process communicates with the API server of the host cluster to schedule the pods and keep track of their state. vcluster appends the name of the virtual cluster namespace the pods are running in and the name of the virtual cluster, to prevent collisions.

The state of most objects running in the virtual cluster is stored in a database inside it. vcluster uses SQLite by default for that DB, but it can also use etcd or a few other options like PostgreSQL. But pods are scheduled in the host cluster.

See the docs if you’d like to learn more about the vcluster architecture.

5. Other helpful commands

Let’s look at a few more things you can do with the vcluster CLI.

First, let’s list the virtual clusters running in our host cluster. 

vcluster list

 NAME          NAMESPACE              STATUS    CONNECTED   CREATED                         AGE   CONTEXT
 my-vcluster   vcluster-my-vcluster   Running               2023-02-17 16:21:50 -0800 PST   26s   docker-desktop

You’ll see the my-vcluster virtual cluster and some additional details about it. This is handy for times when you might not remember which virtual clusters you’ve launched.

We can also pause the vcluster. 

vcluster pause my-vcluster

You should see output like this:

info   Scale down statefulSet vcluster-my-vcluster/my-vcluster...
info   Delete 3 vcluster workloads
done √ Successfully paused vcluster vcluster-my-vcluster/my-vcluster

The vcluster pause command changes the number of replicas in StatefulSets and ReplicaSets to zero. This suspends all of your running pods while preserving all of the other configurations and state in the virtual cluster.

Let’s look at what’s running in the namespace for the virtual cluster now.

kubectl get pods -n vcluster-my-vcluster

You should see this output:

No resources found in vcluster-my-vcluster namespace.

The vcluster itself is a StatefulSet, so even the my-vcluster-0 pod and the CoreDNS pod are scaled down, as well as the Nginx pods we had launched.

Before vcluster sets the replicas to zero, though, it makes an annotation of the current number of replicas. We can spin everything back up with this command:

vcluster resume my-vcluster

The pods will spin back up. This is a very fast and easy way to suspend and resume your workloads in virtual clusters

Virtual clusters are rapid to provision and destroy, though, so you may prefer to delete the virtual cluster entirely. You can do that with:

vcluster delete my-vcluster

It should just take a few seconds, and your output will look like this:

info   Delete vcluster my-vcluster...
done √ Successfully deleted virtual cluster my-vcluster in namespace vcluster-my-vcluster
done √ Successfully deleted virtual cluster namespace vcluster-my-vcluster

All of the resources running in the virtual cluster are cleaned up with vcluster delete.

vcluster Demo Video

Use cases

So what can you do with vcluster? Lots of things. Some popular use cases we’ve seen are:

Dev environments for local or remote development.  The fact that virtual clusters are so lightweight and fast makes them very suitable for remote development in shared clusters, but you can use them on your laptop too. Rather than having to reset/rebuild your local cluster repeatedly, you can delete a virtual cluster and create a new one in seconds.

CI/CD pipelines. Sometimes in a test suite, you reach a point where you want to wipe out the current test environment and start with a fresh, new one. If you are provisioning clusters with your cloud provider’s managed Kubernetes offering, you may wait 10-20 minutes for that new cluster. That time adds up and interferes with your developers getting fast feedback. Running those tests in virtual clusters can be much quicker and more efficient.

Testing against multiple versions of Kubernetes. Are you developing an operator or an app that you’d like to test against several different versions of Kubernetes? You can spin up multiple virtual clusters running different Kubernetes versions very quickly using vcluster’s --version flag.

Training and workshops. Do you need to provision many Kubernetes clusters for a technical training session or workshop? You can do that in a shared Kubernetes cluster with vcluster in a fraction of the time and cost it would take to give every attendee their own cluster.

Can you think of other use cases? If you have a workflow where you must provision and destroy clusters quickly and cheaply, vcluster can help. vcluster is also a certified Kubernetes distribution, which means it passes a suite of conformance tests from the CNCF. So it can be relied on.

To learn more

Many resources for learning more about vcluster are linked at the website, vcluster.com, including the docs and the GitHub repository.

We also host a community Slack with a vcluster channel, which is a great place to chat with the maintainers and other users if you have any questions. You can sign up for it here.

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