Substitutes now also available from bordeaux.guix.gnu.org

Christopher Baines — 18 juin 2021

There have been a number of different project operated sources of substitutes, for the last couple of years the default source of substitutes has been ci.guix.gnu.org (with a few different URLs).

Now, in addition to ci.guix.gnu.org, bordeaux.guix.gnu.org is a default substitute server.

Put that way, this development maybe doesn't sound particularly interesting. Why is a second substitute server useful? There's some thoughts on that exact question in the next section. If you're just interested in how to use (or how not to use) substitutes from bordeaux.guix.gnu.org, then you can just skip ahead to the last section.

Why a second source of substitutes?

This change is an important milestone, following on from the work that started on the Guix Build Coordinator towards the start of 2020.

Back in 2020, the substitute availability from ci.guix.gnu.org was often an issue. There seemed to be a number of contributing factors, including some parts of the architecture. Without going too much in to the details of the issues, aspects of the design of the Guix Build Coordinator were specifically meant to avoid some of these issues.

While there were some very positive results from testing back in 2020, it's taken so long to bring the substitute availability benefits to general users of Guix that ci.guix.gnu.org has changed and improved significantly in the meantime. This means that any benefits in terms of substitute availability are less significant now.

One clearer benefit of just having two independent sources of substitutes is redundancy. While the availability of ci.guix.gnu.org has been very high (in my opinion), having a second independent substitute server should mean that if there's a future issue with users accessing either source of substitutes, the disruption should be reduced.

I'm also excited about the new possibilities offered by having a second substitute server, particularly one using the Guix Build Coordinator to manage the builds.

Substitutes for the Hurd is already something that's been prototyped, so I'm hopeful that bordeaux.guix.gnu.org can start using childhurd VMs to build things soon.

Looking a bit further forward, I think there's some benefits to be had in doing further work on how the nar and narinfo files used for substitutes are managed. There are some rough plans already on how to address the retention of nars, and how to look at high performance mirrors.

Having two substitute servers is one step towards stronger trust policies for substitutes (as discussed on guix-devel, where you would only use a substitute if both ci.guix.gnu.org and bordeaux.guix.gnu.org have built it exactly the same. This would help protect against the compromise of a single substitute server.

Using substitutes from bordeaux.guix.gnu.org

If you're using Guix System, and haven't altered the default substitute configuration, updating guix (via guix pull), reconfiguring using the updated guix, and then restarting the guix-daemon should enable substitutes from bordeaux.guix.gnu.org.

If the ACL is being managed manually, you might need to add the public key for bordeaux.guix.gnu.org manually as well.

When using Guix on a foreign distribution with the default substitute configuration, you'll need to run guix pull as root, then restart the guix-daemon. You'll then need to add the public key for bordeaux.guix.gnu.org to the ACL.

guix archive --authorize < /root/.config/guix/current/share/guix/bordeaux.guix.gnu.org.pub

If you want to just use ci.guix.gnu.org, or bordeaux.guix.gnu.org for that matter, you'll need to adjust the substitute urls configuration for the guix-daemon to just refer to the substitute servers you want to use.