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nixrbd - NixOS Remote Boot Daemon

A daemon that serves NixOS clients booting over iPXE.

This project is under active development. It is perfectly usable right now, but the feature set and command syntax can change without any notice. I will do my best to keep this README up to date with the current code, but I make no promises. There is a version number defined in the code, but it has no real connection to the current state of the code. There are no proper releases yet.

Build and install

It easy to build nixrbd if you have Nix set up properly. Run the following command in the repository root:

nix-env -i -f . \
  -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-15.09.tar.gz

This will install nixrbd in your Nix profile and make it available in your path.

Configure and run

nixrbd is really an HTTP server that lets you use Nix expressions to handle requests. Strictly speaking, you can use it to serve whatever content you'd like over HTTP, not only iPXE scripts. But since this project is about remote booting, it aims to also provide tools and libraries to make it easy to build custom boot environments on top of the core nixrbd server.

Basic usage

You need a working Nix setup to be able to run nixrbd. The Nix utilities (nix-instantiate, nix-store, etc) need to be in the path when running nixrbd.

The following command launches nixrbd with a single request handler (menu-simple.nix):

nixrdb -r /,nix:///absolute/path/to/menu-simple.nix

nixrbd will now run in the foreground and listen for HTTP requests on its default port 8000.

A request handler is a Nix expression that should be buildable with nix-build, and must produce a single file as its output. On an incoming HTTP request, nixrbd will build the expression and serve the resulting file to the HTTP client.

In the example above, the menu-simple.nix could look like this:

{ request, ... }:

with import <nixpkgs> {};

writeText "menu.ipxe" ''
  #!ipxe

  :menu_root
  menu Select a boot alternative
  item memtest Run Memtest
  item shell   Enter iPXE shell
  choose target && goto ''${target} || goto menu_root

  :shell
  shell && goto menu_root

  :memtest
  chain http://boot.ipxe.org/memtest.0
''

This creates a simple menu with two options: either boot to the iPXE shell, or run memtest.

You can now make an HTTP request and verify that nixrbd correctly builds and serves your Nix expression:

$ curl http://localhost:8000
#!ipxe

:menu_root
menu Select a boot alternative
item memtest Run Memtest
item shell   Enter iPXE shell
choose target && goto ${target} || goto menu_root

:shell
shell && goto menu_root

:memtest
chain http://boot.ipxe.org/memtest.0

Routes

When launching nixrbd you can give it an arbitrary number of routes as -r or --route command line options. Each route has the following form:

<request uri>,<response uri>

The request URI is relative the root (the initial / is optional), and nixrbd will match every incoming requests against all specified routes. The most specific route that still matches the request will be picked. Say you have the following routes defined:

-r /foo,<B>
-r /,<A>
-r /foo?host=myhost,<C>

Then the requests would be handled as below:

/                    -> A
/foobar              -> A
/foo/bar             -> B
/foo?host=yourhost   -> B
/foo/bar?host=myhost -> C

The route target (the response URI) can be of tree types: static file, nix build and empty response with pre-defined status code.

Testing nixrbd together with iPXE

The utils folder in the repository root includes a test script that automatically launches both a nixrbd instance and a qemu instances that boots with an iPXE image that chain-loads the script that nixrbd serves. This way, you can try out your boot scripts in a virtual environment. The following example makes use of a sample menu (menu-simple.nix) that also is bundled with nixrbd:

utils/start_qemu -r /nix/store,file:///nix/store -r /,nix://`pwd`/utils/menu-simple.nix

All arguments to the script will be forwarded directly to nixrbd. The script will build nixrbd, ipxe and qemu, and bring up your boot menu/script in a qemu window.