[davidopp__]

I don't think multi-tenancy has been "retrofitted" onto Kubernetes. Kubernetes was designed with multi-tenancy in mind from the very early releases -- namespaces, authn/authz (initially ABAC, later RBAC), ResourceQuota, PodSecurityPolicy, etc. New features are added over time, such as NetworkPolicy (which has been in Kubernetes for a year and a half, so perhaps not "new" anymore!), EventRateLimit, and others, but always in a principled way. And the integration of container isolation technologies like gVisor and Kata are using a standard Kubernetes extension point (the Container Runtime Interface) so I do not view this work as retrofitting.

Moreover, even today there are real public PaaSes that expose the Kubernetes API served by a multi-tenant Kubernetes cluster to mutually untrusting end-users, e.g. OpenShift Online and one of the Huawei cloud products (I forget which one). Obviously Kubernetes multi-tenancy isn't going to be secure enough today for everyone, especially folks who want an additional layer of isolation on top of cgroups/namespaces/seccomp/AppArmor/etc., but there are a lot of advantages to minimizing the number of clusters. (See my other comment in this thread about the pattern we frequently see of separate clusters for dev/test vs. staging vs. prod, possibly per region, but sharing each of those among multiple users and/or applications.)

Disclosure: I work at Google on Kubernetes and GKE.

[raesene9]

From a security (as opposed to workload isolation) perspective, I don't think k8s was designed with multi-tenancy in mind at all, in early versions.

Definitely I've had conversations with some of the project originators where it was clear the security boundry was intended to be cluster level in early versions.

Some of the security weaknesses in earlier versions (e.g. no AuthN on the kubelet, cluster-admin grade service tokens etc) make that clear.

Now it's obv. that secure hard multi-tenancy is a goal going forward (and I'll be very interested to see what the 3rd party audit throws up in that regard), but it is a retro-fit.

[jacques_chester]

> I don't think multi-tenancy has been "retrofitted" onto Kubernetes. Kubernetes was designed with multi-tenancy in mind from the very early releases -- namespaces, authn/authz (initially ABAC, later RBAC), ResourceQuota, PodSecurityPolicy, etc.

My complaint is that these require assembly and are in many cases opt-in (making RBAC opt-out was a massive leap forward).

Namespaces are the lynchpin, but are globally visible. In fact an enormous amount of stuff tends to wind up visible in some fashion. And I have to go through all the different mechanisms and set them up correctly, align them correctly, to create a firmer multi-tenancy than the baseline.

Put another way, I am having to construct multi-tenancy inside multiple resources at the root level, rather than having tenancy as the root level under which those multiple resources fall.

> there are a lot of advantages to minimizing the number of clusters.

The biggest is going to be utilisation. Combining workloads pools variance, meaning you can safely run at a higher baseline load. But I think that can be achieved more effectively with virtual kubelet .

[davidopp__]

> The biggest is going to be utilisation. Combining workloads pools variance, meaning you can safely run at a higher baseline load.

Utilization is arguably the biggest benefit (fewer nodes if you can share nodes among users/workloads, fewer masters if you can share the control plane among users/workloads), but I wouldn't under-estimate the manageability benefit of having fewer clusters to run. Also, for applications (or application instances, e.g. in the case of a SaaS) that are short-lived, the amount of time it takes to spin up a new cluster to serve that application (instance) can cause a poor user experience; spinning up a new namespace and pod(s) in an existing multi-tenant cluster is much faster.

> But I think that can be achieved more effectively with virtual kubelet .

I think it's hard to compare virtual kubelet to something like Kata Containers, gVisor, or Firecracker. You can put almost anything at the other end of a virtual kubelet, and as others have pointed out in this thread virtual kubelet doesn't provide the full Kubelet API (and thus you can't use the full Kubernetes API against it). At a minimum I think it's important to specify what is backing the virtual kubelet, and what Kubernetes features you need, in order to compare it with isolation technologies like the others I mentioned.

Disclosure: I work at Google on Kubernetes and GKE.