It's still containers. On a cloud provider the Kubernetes workers are VM's which orchestrate containers. With Kata Containers you're just spawning containers inside micro-vm's.
The security profiles of containers and VMs, including kernel-based VMs, are different. VMs still have a significant edge, because the attack surface is smaller and doesn't have many competing missions.
I wonder how many multi-tenant workloads are actually at risk of an escape vulnerability. I wager that the multi-tenancy described in the article in the OP is actually disparate workloads across disparate teams in a particular enterprise where it seems (to me) fairly unlikely for someone with access to run a workload to also have the willingness to compile and run malicious code to take advantage of an escape vulnerability.
On the other hand, publicly available compute, i.e. AWS, GCP, Azure seems way more likely to be the subject of attacks from random malicious individuals seek to take advantage of an escape vulnerability if one existed.
And let's not forget the recent CPU exploits which found that VMs aren't very separated after all.
The fact that Kubernetes disables this (and other) security features by default should be seen as a flaw in Kubernetes. (Just as some of the flaws of Docker should be seen as Docker flaws not containers-in-general flaws.)
Yes, though as capabilities are added to the kernel, the profiles have to be updated.
That said, VM or no VM, this should be done no matter what.
> And let's not forget the recent CPU exploits which found that VMs aren't very separated after all.
This is a nil-all draw in terms of the respective security postures, though.
Shared kernel linux containers can be hardened to the point, where they likely have a smaller attack surface than a general purpose hypervisor (for example look at the approach that Nabla takes)
You then have the hybrid approach of gVisor, still containers, but smaller attack surface than the Linux kernel.
Of course this hardening approach can (and should be) applied to VMs too, which may tip the balance back to them, which is one reason that firecracker looks so interesting.
It's not all or nothing either. Containerd will support running a mix of containers and kata-containers across workers.
For anyone interested in this topic I wrote about some other container runtimes here: https://kubedex.com/kubernetes-container-runtimes/