The Firecracker virtual machine monitor

There are folks that just want to use a Docker file to describe a "pet" virtual machine. They are running a single master MySQL database or something else like that that can never be restarted, scales vertically, and generally needs a lot of love.

The other class of containers users are actually doing things that can be called serverless whereas every container is truly "cattle" and can be restarted at will. Function virtualization is the extreme form of cattle here.

There are a lot of simplifying assumptions you can make with cattle. You can avoid the complexity of live migration or live update because you can just restart things. You don't need to worry about hotplug because you can just kill it and start with more CPU/memory or scale out horizontally.

I don't think you can do better than QEMU for pets. It represents a huge amount of effort and a massive amount of learnings. I do think you can have a better VMM for cattle though and that's what we're trying to do with Firecracker.

Kata wants to support both pets and cattles so it will have a multi VMM strategy. I understand why NEMU happened but it's the same mistake that's been made dozens of times before. Heck, KVM started out with a QEMU fork that did a lot of the same things and it took years to undo that.

Ultimately, it's about what your simplifying assumptions are. Saying that you'll never need to run Windows, never need to support PCI passthrough, or never need to run for more than a day at a time lets you experiment with lots of different ideas that weren't possible before.