NixOS Firecracker VM

Motivation for NixOS

Reproducible builds!
Declarative configurations.

Motivation for Using Firecracker VMs

I’ve been playing with Firecracker VMs for a bit now and have become my primary means for PoCing things. And I’ve been wanting to switch to NixOS, but haven’t had the time to move my primary machine."

I’ve been asked “why not Docker? why VMs?” and honestly I don’t have a great technical reason for the decision. It’s mostly from a learning viewpoint that I’ve made this decision.

Steps

Run the following as a non-root user
sh <(curl -L https://nixos.org/nix/install) --daemon
nix-channel --add https://nixos.org/channels/nixos-21.11 nixpkgs
nix-channel --update
nix-env -f '<nixpkgs>' -iA nixos-install-tools
Generate nixos configs

sudo `which nixos-generate-config` --root /mnt

This will create the following:

[foo@archlinux ~]$ ls /mnt/etc/nixos/
configuration.nix           hardware-configuration.nix

Make some minimal tweaks to these generated files

Set the following in /etc/nixos/configuration.nix

users.users.root.initialHashedPassword = "";
boot.loader.grub.device = "nodev"; # or "nodev" for efi only
networking.hostName = "nixos"; # Define your hostname.
time.timeZone = "America/NewYork";
environment.systemPackages = with pkgs; [
  vim
  wget
  firefox
];
services.openssh.enable = true;

Added the following to /etc/nixos/hardware-configuration.nix

  fileSystems."/" = {
    device = "/dev/disk/by-uuid/<uuid>";
    fsType = "ext4";
  };

sudo groupadd -g 30000 nixbld
sudo useradd -u 30000 -g nixbld -G nixbld nixbld
export NIX_PATH=/nix/var/nix/profiles/per-user/root/channels

[foo@archlinux ~]$ sudo PATH="$PATH" NIX_PATH="$NIX_PATH" `which nixos-install` --root /mnt
building the configuration in /mnt/etc/nixos/configuration.nix...
error: file 'nixpkgs/nixos' was not found in the Nix search path (add it using $NIX_PATH or -I)

Found https://github.com/NixOS/nixpkgs/issues/149791#issuecomment-1107865859

Re-run nixos-install

sudo PATH="$PATH" NIX_PATH="$NIX_PATH" `which nixos-install` --root /mnt

sudo chown -R 0:0 /nix
for i in {1..32}; do sudo userdel -f nixbld${i}; done
sudo groupdel nixbld
pacman -S rsync
(on host) sudo mkdir /mnt/nixos-root && sudo rsync -a root@archlinux.localdomain:/mnt /mnt/nixos-root
[root@archlinux ~]# chroot /mnt/ /bin/sh but there’s nothing here except sh and env which is expected from https://nixos.wiki/wiki/Nix_vs._Linux_Standard_Base
Need to set my nix-profile in the chroot

Need to use nixos-enter instead

"NIXOS FIRECRACKER VM"

Motivation for NixOS

Motivation for Using Firecracker VMs

Steps