[GSoC] Rewrite Hydra to be more integrated with Guix.

[Mathieu Lirzin <mthl@gnu.org>]

Hello fellow Guix Hackers,

Being currently a student which is due to make an internship, I intend
to turn this boring administrative injunction into an opportunity to
contribute to Guix by applying to Google Summer of Code which is
considered as an internship by University of Bordeaux standards.

Hydra is a Nix-based continuous build system which is used by Guix to
compile packages on different platforms and to distribute packages
substitutes.  With time, nix-daemon and guix-daemon are evolving
differently.  Hydra being heavily dependent on nix-daemon, Guix is not
able to use its newest versions.  Moreover there are some software
related performance issues (among others) in the current Guix
infrastructure that are unlikely to be solved considering the
foreignness of Hydra Perl implementation to Guix hackers.

In that context, I am willing to work on implementing a continous build
system similar to Hydra in Guile.

This GSoC will not likely succeed in implementing every features Hydra
is currently providing.  The objective is rather to create the basis
which will then allow further developpements to overcomes the present
difficulties.  To achieve this the following milestones (suggested by
Ludo) will be followed:

- Implementing a simple loop pulling Guix Git repository and building
  every packages.
   
- Adding a “job” abstraction to be able to build different Git branches.

- Adding support for a database to keep track of the build results with
  their associated commit, derivation and output.

- Adding a API over HTTP to get the build results remotely (ideally
  through an Emacs interface).

- Adding support for configuring and launching jobs remotely.

Everyone is welcome to provide its input in order to improve the roadmap
or commenting on the global picture.

I have added an entry for this project in the GSoC idea list:

  https://libreplanet.org/wiki/Group:Guix/GSoC-2016#Rewrite_Hydra_to_be_more_integrated_with_Guix

-- 
Mathieu Lirzin