Author of "All you need to know about KVM userspace" here! I am happy that you liked it. Some things have changed since then, some have not...
Red Hat is now shipping Kata Containers, which does not (much to my dismay) use Libvirt, and also KubeVirt which uses Libvirt but not for sandboxing (only to drive QEMU; Kubernetes takes care of the sandboxing by running one VM per pod). But the original architecture is still in use and new users appeared such as cockpit-machine and crun-vm.
Another super interesting project for KVM userspace is libkrun which, among other things, is being used for gaming on Arm Mac's. :)
Firecracker's scope has grown somewhat, in particular it supports snapshots for warm start of VMs.
QEMU's microvm didn't have a huge success but recently Amazon contributed support for running Nitro enclaves in QEMU, which reuses a lot of the microvm code.
Some Rust components have been developed to build virtio devices out of process (for example virtiofsd). QEMU is also experimenting with devices written in Rust, and I expect to have two almost-entirely-safe-Rust devices (converted from C) within a month or two.
Red Hat is now shipping Kata Containers, which does not (much to my dismay) use Libvirt, and also KubeVirt which uses Libvirt but not for sandboxing (only to drive QEMU; Kubernetes takes care of the sandboxing by running one VM per pod). But the original architecture is still in use and new users appeared such as cockpit-machine and crun-vm.
Another super interesting project for KVM userspace is libkrun which, among other things, is being used for gaming on Arm Mac's. :)
Firecracker's scope has grown somewhat, in particular it supports snapshots for warm start of VMs.
QEMU's microvm didn't have a huge success but recently Amazon contributed support for running Nitro enclaves in QEMU, which reuses a lot of the microvm code.
Some Rust components have been developed to build virtio devices out of process (for example virtiofsd). QEMU is also experimenting with devices written in Rust, and I expect to have two almost-entirely-safe-Rust devices (converted from C) within a month or two.