MicroVM.nix
A Nix Flake to build NixOS and run it on one of several Type-2
Hypervisors on NixOS/Linux. 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
impereratively with the provided microvm
command.
Warning: This is a Nix Flakes-only project. Use with nix-shell -p nixFlakes
At a glance
- MicroVMs are Virtual Machines but use special device interfaces (virtio) for high performance
- This project runs them on NixOS hosts
- You can choose one of five hypervisors for each MicroVM
- MicroVMs have a fixed RAM allocation (default: 512 MB)
- MicroVMs have a read-only root disk with a prepopulated
/nix/store
- You define your MicroVMs in a Nix Flake's
nixosConfigurations
section, reusing thenixosModules
that are exported by this Flake - MicroVMs can access stateful filesystems either on a image volume as a block device or as a shared directory hierarchy through virtiofsd.
- Zero, one, or more virtual tap ethernet network interfaces can be attached to a MicroVM.
Hypervisors
Hypervisor | Language | Restrictions |
---|---|---|
qemu | C | |
cloud-hypervisor | Rust | |
firecracker | Rust | no virtiofs shares |
crosvm | Rust | no virtiofs shares, no network interfaces |
kvmtool | C | no virtiofs shares |
Installation
nix registry add microvm github:astro/microvm.nix
(If you do not want to inflict this change on your system, just
replace microvm
with github:astro/microvm.nix
in the following
examples.)
Start your own NixOS MicroVM definitions
nix flake init -t 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
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
MicroVMs. They listen for ssh with an empty root password.
NixOS modules
microvm.nixosModules.host
Use this on a (physical) machine that is supposed to host MicroVMs.
Declarative MicroVMs configuration
Declare MicroVMs in your host's nixosSystem.
This method is meant to be used to ensure the presence of a
MicroVM. It will not update preexisting MicroVMs in
/var/lib/microvm
. Use the imperative microvm
command to do that.
microvm.vms."my-microvm" = {
# Source flake for `nixos-rebuild` of the host
flake = self;
# Source flakeref for `microvm -u my-microvm`
updateFlake = "git+https://...";
};
Imperative MicroVM management
# Create my-microvm
microvm -f git+https://... -c my-microvm
# Update my-microvm
microvm -u my-microvm
# List MicroVMs
microvm -l
microvm.nixosModules.microvm
Import this module in your MicroVM's nixosSystem. Refer to nixos-modules/microvm/options.nix for MicroVM-related config.
Migrating from 0.1.0 to 0.2.0
Your Flake does no longer need to provide the MicroVMs as packages. An
entry for each MicroVM in nixosConfiguration
is enough.
To get a MicroVM's hypervisor runner as a package, use:
nix build myflake#nixosConfigurations.my-microvm.config.microvm.runner.qemu
MicroVM parameters have moved inside the NixOS configuration, gaining
parameter validation through the module system. Refer to
nixos-modules/microvm/options.nix
for their definitions.
Cleaning up /var/lib/microvms/*
Delete the following remnants from 0.1.0:
microvm-run
microvm-shutdown
tap-interfaces
virtiofs
All these copied files are now behind the current
symlink to a
Hypervisor runner package.
At last, check the validity of the symlinks in
/nix/var/nix/gcroots/microvm
.
Commercial support
The author can be hired to implement the features that you wish, or to
integrate this tool into your toolchain. If in doubt, just press the
Ideas
- Boot with root off virtiofs, avoiding overhead of creating squashfs image
- Provide a writable
/nix/store
- Distribute/fail-over MicroVMs at run-time within a cluster of hosts