network booting nixos

server-configuration.nix

{ ... }:

{
  imports = [ ./tgt_service.nix ];
  services = {
    atftpd.enable = true;
    atftpd.root = "/tftproot";
    tgtd = {
      enable = true;
      targets = {
        # backing store can be a file made with truncate(1)
        "iqn.2016-01.laptop-root" = { backingStore = "/dev/naspool/laptop-root"; index = 1; };
      };
    };
  };
}

#1

[root@amd-nixos:~]# nix-build '<nixpkgs>' -A ipxe
these paths will be fetched (0.60 MiB download, 1.20 MiB unpacked):
  /nix/store/1xw30y28dfc1wz62wgcjifsp58c8wdkk-ipxe-20141124-5cbdc41
fetching path ‘/nix/store/1xw30y28dfc1wz62wgcjifsp58c8wdkk-ipxe-20141124-5cbdc41’...

*** Downloading ‘https://cache.nixos.org/nar/1sksixb1cc57ypjmm99k274wfmc3mqbrvnbvyilz0sd8h8bnyn0l.nar.xz’ (signed by ‘cache.nixos.org-1’) to ‘/nix/store/1xw30y28dfc1wz62wgcjifsp58c8wdkk-ipxe-20141124-5cbdc41’...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  614k  100  614k    0     0  1170k      0 --:--:-- --:--:-- --:--:-- 1172k

/nix/store/1xw30y28dfc1wz62wgcjifsp58c8wdkk-ipxe-20141124-5cbdc41

[root@amd-nixos:~]# mkdir /tftproot/

[root@amd-nixos:~]# cp -vi result/undionly.kpxe /tftproot/

#2

setup a tgt daemon using the tgt_module and tftp server
configure and rebuild-switch the server with server-configuration.nix

#3

setup dhcp to direct users to the tftp server with ipxe using the dhcp fragment

192.168.2.61 is the IP of the tftp and http server

dhcp fragment

        subnet 192.168.2.0 netmask 255.255.255.0 {
          option subnet-mask 255.255.255.0;
          option broadcast-address 192.168.2.255;
          option routers 192.168.2.1;
          range 192.168.2.100 192.168.2.200;
          next-server 192.168.2.61;
          if exists user-class and option user-class = "iPXE" {
            filename "http://192.168.2.61/boot.php?mac=${net0/mac}&asset=${asset:uristring}";
          } else {
            filename = "undionly.kpxe";
          }
        }

tgt_service.nix

{ config, lib, pkgs, ... }:

with lib;

let
  targetOpts = { name, config, ... }: {
    options = {
      name = mkOption {
        type = types.str;
      };
      backingStore = mkOption {
        type = types.str;
      };
      index = mkOption {
        type = types.int;
        description = "the index of the target, must be unique within the server";
      };
    };
    config = {
      name = mkDefault name;
    };
  };
      makeService = target: {
        name = target.name;
        value = {
          description = target.name+" auto-starter";
          wantedBy = [ "basic.target" ];
          partOf = [ "tgtd.service" ];
          script = ''
            ${pkgs.tgt}/bin/tgtadm --lld iscsi --op new --mode target --tid ${builtins.toString target.index} -T ${target.name}
            ${pkgs.tgt}/bin/tgtadm --lld iscsi --op new --mode logicalunit --tid ${builtins.toString target.index} --lun 1 -b ${target.backingStore}
            ${pkgs.tgt}/bin/tgtadm --lld iscsi --op bind --mode target --tid ${builtins.toString target.index} -I ALL # gives everybody access
          '';
          serviceConfig = {
            Type = "oneshot";
            RemainAfterExit = true;
            ExecStop = "${pkgs.tgt}/bin/tgtadm --lld iscsi --op delete --mode target --tid ${builtins.toString target.index}";
          };
        };
      };
in
{
  options = {
    services.tgtd = {
      enable = mkOption {
        type = types.bool;
        default = false;
        description = "enable tgtd running on startup";
      };
      targets = mkOption {
        default = [];
        type = types.loaOf types.optionSet;
        options = targetOpts;
      };
    };
  };
  config = let
      LUNs = builtins.listToAttrs (map makeService (attrValues config.services.tgtd.targets));
      tgtd = {
        description = "tgtd daemon";
        wantedBy = [ "basic.target" ];
        serviceConfig = {
          ExecStart = "${pkgs.tgt}/bin/tgtd -f --iscsi nop_interval=30 --iscsi nop_count=10";
          ExecStop = "${pkgs.coreutils}/bin/sleep 30 ; ${pkgs.tgt}/bin/tgtadm --op delete --mode system";
          KillMode = "process";
          Restart = "on-success";
        };
      };
    in
     mkIf config.services.tgtd.enable {
      systemd.services = LUNs // { tgtd = tgtd; };
    };
}