Update: I don't think this will work correctly either, since the component derivations' outputs are also directories rather than individual files 🤦‍♂️

That's not a problem as long as the derivation emits a hydra-build-products file (similar to the ISO image jobs).

Yes, I realised this earlier. However, since A) these derivations aren't actually hydra jobs and B) the netboot files are symlinks (NixOS/hydra#580), this doesn't work yet.

Fixed! Things to note:

• I made AWS upload optional, so that I could test the script to some extent myself
• I reworked downloadFile to support multiple build products
• Netboot is ignored if downloading it fails, because not all current channels currently contain nixos/release: use real paths of netboot files nixpkgs#44089

Some questions:

• How will netboot.xyz find these files?

• What filename are they uploaded to? I gather it's {netboot.ipxe,initrd,bzImage}. In that case they should really be put in a subdirectory since having files names initrd or bzImage is not very informative.

• I gather from NixOS support netbootxyz/netboot.xyz#37 that netboot.xyz can use ISOs directly. That would be much preferred to adding yet another big image to our release process. Why can't we do that?

• In https://hydra.nixos.org/build/79499085 I see a 440 MiB initrd, which seems rather big for an initrd. Does it contain the entire Nix store or something? Doesn't that require the entire initrd to be decompressed into memory?

Aside: the ideal netboot would be to have a minimal initrd that mounts cache.nixos.org on /nix/store (via NixOS/nix@a9cbd67) and boots the system closure from there.

How will netboot.xyz find these files?

After this, they should be available at https://nixos.org/channels/nixos-{18.03,unstable}/netboot.ipxe.

What filename are they uploaded to? I gather it's {netboot.ipxe,initrd,bzImage}. In that case they should really be put in a subdirectory since having files names initrd or bzImage is not very informative.

That makes sense, I can try doing that.

I gather from netbootxyz/netboot.xyz#37 that netboot.xyz can use ISOs directly. [snip] Why can't we do that?

It's unable to find the root filesystem, for reasons similar to boot failures caused by incorrect USB stick creation.

much preferred to adding yet another big image to our release process

These files are already built by hydra, does including them on the channel page make a big difference?

Does it contain the entire Nix store or something? Doesn't that require the entire initrd to be decompressed into memory?

Yes and no respectively. It contains the entire nix store as a squashfs (much like the CD image), which is mounted and decompressed on the fly.

Aside: the ideal netboot would be to have a minimal initrd that mounts cache.nixos.org on /nix/store (via NixOS/nix@a9cbd67) and boots the system closure from there.

That is awesome! Orthogonal to this change, but it should allow making the initrd a bit smaller in future versions.

ping @lheckemann

zram and zstd might help with the size: NixOS/nixpkgs#52991

@Mic92 current zramSwap module isn't designed to be started in stage1. Also, if that squashfs @lheckemann mentions is already compressed, then it can't be compressed more, and thus no extra memory gain.

This snippet by @Lassulus would download the iso in the initrd:

{ pkgs, lib }: let
  system = import <nixpkgs/nixos/lib/eval-config.nix> {
    modules = [{
      imports = [
        <nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-base.nix>
      ];
      boot.initrd.network.enable = true;
      boot.devSize = "500m";
      boot.initrd.kernelModules = [ "e1000" ];
      boot.initrd.extraUtilsCommands =''
        cp ${pkgs.stdenv.cc.libc}/lib/libnss_dns.so.* $out/lib/
      '';
      boot.initrd.network.postCommands = ''
        wget 'https://d3g5gsiof5omrk.cloudfront.net/nixos/18.09/nixos-18.09.1922.97e0d53d669/nixos-minimal-18.09.1922.97e0d53d669-x86_64-linux.iso' -O /dev/root
      '';
      boot.initrd.postMountCommands = ''
        export stage2Init=$(awk '/APPEND/ {for(i=1;i<=NF;i++){ if($i ~ /init/){split($2,a,"="); print a[2]; exit} } }' /mnt-root/iso/isolinux/isolinux.cfg)
      '';
    }];
  };
in pkgs.writeScript "run" ''
  #!/bin/sh
  ${pkgs.kvm}/bin/qemu-kvm -m 2G \
    -kernel ${system.config.system.build.kernel}/bzImage \
    -initrd ${system.config.system.build.initialRamdisk}/initrd \
    -net nic,netdev=user.0,model=e1000 -netdev user,id=user.0,hostfwd=tcp::8022-:22 \
    -append "console=ttyS0 copytoram" -nographic
''

This pull request has been mentioned on Nix community. There might be relevant details there:

https://discourse.nixos.org/t/easy-to-use-nixos-image-generators/1887/4

Do the images that netboox.xyz uses work?
Is it enough to have netbook fetch them from Hydra? Wouldn't it be nice to have it in the channel?

That doesn't finish for me, even after a few minutes:

$ wget https://hydra.nixos.org/job/nixos/trunk-combined/nixos.netboot.x86_64-linux/latest-finished/download/netboot.ipxe
--2019-07-04 23:04:11--  https://hydra.nixos.org/job/nixos/trunk-combined/nixos.netboot.x86_64-linux/latest-finished/download/netboot.ipxe
Resolving hydra.nixos.org (hydra.nixos.org)... 46.4.67.10, 2a01:4f8:140:248f::
Connecting to hydra.nixos.org (hydra.nixos.org)|46.4.67.10|:443... connected.
HTTP request sent, awaiting response... 

I just tested it inside a qemu VM, the unstable channel image works, even though the wget also does nothing for me.
Would still be nice to have the netboot stuff in the channel to have it on a faster server. But as long as it works I'm happy