STATUS: Proof Of Concept

k3v runs as a dedicated virtual Kubernetes control plane. When pods are launched they are launched in another cluster. k3v uses the compute, storage, and networking resources from a real Kubernetes cluster. This allows one to take one physical Kubernetes cluster and chop it up into smaller virtual clusters. Also, it is theoretically possible that one virtual cluster spans multiple physical clusters.

Please note, this is POC quality stuff.

1. Download k3v binary from the releases page. NOTE: While Windows and macOS binaries are available they probably won't work.
2. Run k3v pointing to a kubeconfig file of your physical cluster.

   ./k3v --kubeconfig someconfig.yaml

   If you kube config is in the standard $HOME/.kube/config then no argument is needed.
3. Once started k3v will create a local folder ./k3v-data that has the virtual kubernetes state. Also ./kubeconfig.yaml will be created.
4. Use ./kubeconfig.yaml to talk to k3v

   kubectl --kubeconfig ./kubeconfig.yaml --all-namespaces=true get all

The reasons for experimenting with virtual clusters are

1. Better security/multitenancy
2. Better separation of concerns between infra and custom controllers (operators)
3. Ability to package complex k8s based applications

Virtual clusters can help create a better model for hard multi tenancy.

Multitenancy in Kubernetes is hard for multiple reasons. First you must trust the security of a container. Meaning that one bad neighbor can't attack another neighbor. Virtual clusters does not help with this concern. To address this you need to trust containers or leverage another technology like gvisor or katacontainers. The second and more fundamental issue is that the attach surface of Kubernetes is far to large for multitenancy. Right now the only way to accomplish multi tenancy is to not allow users to do the vast majority of Kubernetes operations. It is far too difficult to ensure that all the various APIs will not expose some issue. But limiting access means an end user can't leverage a lot of functionality of Kubernetes, such as operators.

Virtual clusters allow you to separate out the problem into two distinct layers. First you need a secure and very limited physical cluster. A virtual cluster only requires very basic CRUD privileges on pods, services, endpoints, configmap, secrets, and pvcs. It is far easier to secure this small set of APIs. Then tenants can be given access to a virtual kubernetes instance and given full cluster admin privileges. They can do whatever they want with Kubernetes and you can be confident they won't impact another neighbor.

Kubernetes is a great architecture that allows one to write things such as operators or controllers to manage your infrastructure. Unfortunately each operator or controller you add to a cluster could have larger impacts on the cluster. Today, if you want an operator, really a cluster admin must install that for you. And more importantly, the cluster admin must have confidence the operator won't do harm to the cluster. This is not a scalable model.

With virtual clusters you can setup large, rather boring physical clusters. One team can be responsible for the core uptime of this cluster. Then each virtual cluster can install operators or any random component as they wish, with a high degree of confidence that if something goes wrong it only impacts this one virtual cluster.

If you write a complex Kubernetes based application (think istio or such) one could package this application in a virtual cluster and deploy it in a cluster much like a normal controller, but with no CRDs. No matter what madness that application does (CRDs, finalizers, webhooks, etc) it is all nicely encapsulated.

Copyright (c) 2019 Rancher Labs, Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

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