MicroVM.nix

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A Nix Flake to build NixOS and run it on one of several Type-2 Hypervisors on NixOS/Linux or macOS. The project is intended to provide a more isolated alternative to nixos-container. You can either build and run MicroVMs like Nix packages, or alternatively install them as systemd services declaratively in your host's Nix Flake or imperatively with the provided microvm command.

Project Presentation (video)

At a glance

• MicroVMs are Virtual Machines but use special device interfaces (virtio) for high performance.
• This project runs them on NixOS/Linux hosts and macOS (via vfkit).
• You can choose from eight hypervisors for each MicroVM.
• MicroVMs have a fixed RAM allocation (default: 512 MB) but can be shrunk using microvm-balloon
• MicroVMs have a read-only root disk with either a prepopulated /nix/store or by mounting the host's along with an optional writable overlay. This filesystem can be built as either squashfs (smaller) or erofs (faster).
• You define your MicroVMs in a Nix Flake's nixosConfigurations section, reusing the nixosModules that are exported by this Flake.
• MicroVMs can access stateful filesystems either on a image volume as a block device, or alternatively as a shared directory hierarchy through 9p or virtiofs.
• Zero, one, or more virtual tap ethernet network interfaces can be attached to a MicroVM. qemu, kvmtool, and vfkit also support user networking which requires no additional setup on the host.
• For high-throughput TAP networking with qemu, enable tap.vhost = true to use vhost-net kernel acceleration (~10 Gbps vs ~1.5 Gbps without).

Hypervisors

Hypervisor	Language	Restrictions
qemu	C
cloud-hypervisor	Rust	no 9p shares
firecracker	Rust	no 9p/virtiofs shares
crosvm	Rust	9p shares broken
kvmtool	C	no virtiofs shares, no control socket
stratovirt	Rust	no 9p/virtiofs shares, no control socket
alioth	Rust	no virtiofs shares, no control socket
vfkit	Go	macOS only, no 9p shares, no tap/bridge networking

Installation

nix registry add microvm github:microvm-nix/microvm.nix

(If you do not want to inflict this change on your system, just replace microvm with github:microvm-nix/microvm.nix in the following examples.)

Start writing your own NixOS MicroVM definitions

nix flake init -t microvm
$EDITOR flake.nix
nix run .#my-microvm

Examples

Run MicroVMs on your local machine

nix run microvm#qemu-example
nix run microvm#firecracker-example
nix run microvm#cloud-hypervisor-example
nix run microvm#crosvm-example
nix run microvm#kvmtool-example
nix run microvm#stratovirt-example

# On macOS only:
nix run microvm#vfkit-example

Run a MicroVM example with nested MicroVMs on 5 different Hypervisors

nix run microvm#vm

Check networkctl status virbr0 for the DHCP leases of the nested MicroVMs. They listen for ssh with an empty root password.

Experimental: run graphical applications with graphics support

On Linux with cloud-hypervisor and Wayland forwarding:

nix run microvm#graphics neverball

On macOS with vfkit, enable graphics with microvm.graphics.enable = true.

Commercial support

Accelerate your operations and secure your infrastructure with support from a team of virtualization experts. Contact Cyberus Technology: https://www.cyberus-technology.de/contact

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