New build farm

[Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>]

Hi Guix,

in the past weeks I’ve restored some unused servers and turned them into
a secondary build farm.  It consists of 12 servers of which 11 are
currently in use (I broke one by accidentally deleting the bootloader,
oops).

The head of this build farm is available as <https://berlin.guixsd.org>.
It currently builds substitutes for x86_64.

Feel free to use it to satisfy your substitution needs.  You will have
to authorize the build farm’s signing key to use the substitutes:

--8<---------------cut here---------------start------------->8---
wget https://git.savannah.gnu.org/cgit/guix/maintenance.git/plain/hydra/keys/guix/berlin.guixsd.org-export.pub
sudo su
guix archive --authorize < berlin.guixsd.org-export.pub
exit
--8<---------------cut here---------------end--------------->8---

This build farm uses Cuirass, which is still much less convenient than
Hydra, but I hope that by using it in production we will have a better
understanding of what features we will need to implement next.

I should also say that I have previously observed truncation of
substitutes on slow connections and I suspect that there’s a problem
with the firewall settings at this site.  I’ll keep investigating this.

Thanks to Ludo and Andreas for the assistance with debugging the
configuration and setting up DNS, and to the MDC Berlin (the institute
where I spend most of the daylight hours of the week) for not only
letting me use the servers but also for hosting them.

-- Ricardo