FOSDEM 2025

Conference Report

So for the nth time, I visited Brussels this weekend for FOSDEM.

Friday

  • ✅ Flight in
  • ✅ Check into airbnb
  • ✅ Meet up with friends
  • ✅ A beer and some food. (all you can eat ribs!)
  • ✅ Brewdog for upcloud's free beer event.
    Quite pretty nice, met some finish people who are arranging (Disobey)[https://disobey.fi/2025/] in helsinki in a couple of weeks.
    • a Nordic white hat security conference.

Woke on Saturday, shaked off the cobwebs and head to the ULB.

packed

Welcome Keynote was Packed!

25th Fosdem, by far the largest open source conference in Europe.

Containers and virtualization devroom

Spegel

  • Very interesting talk about a stateless OCI registry.
  • Runs on all your nodes, uses P2P to get images from other nodes.
  • Both cost and performance improvements. (author saw up to 80% improvement in startup)
  • Something we will explore for our CI cluster.

Current/Max CPU in Containers

  • This is a discussion about a new linux cgroups flag to set max cpu concurrency.
  • Was interesting, quite technical but not immediately something I see our team using.

Incus and OCI App Containers

  • Incus is something I learned about last year, and it's a very interesting project.
  • This talk was about they have extended incus to support running app containers.
  • Allow running your container more like a vm, with a VIP, and being able to adjust resources on the fly.
  • Example was zigbee2mqtt, which is a project I use at home. Might explore this for my home setup.

Nix Devroom

  • After the devroom, I grabbed a quick lunch and headed to the Nix devroom.
  • Was full
  • Camped at the door for one talk, and got in for a few talks.

How I built a LTE router with a 60$ laptop and nix.

  • Talk by a nix newibie about how he setup a simple router for cameras in his home renovation project.
  • This might be a nice introduction to nix for people who are not familiar with it, good presenter.

Remote Execution with Buck2 and Nix

  • Interesting talk about monorepo tooling and how they use buck2 with nix to build and test their code.
  • Why are they using buck2? Allows you to target items on a more granular level than nix, caching.

system-manager

  • Run services from nix on other distributions.
  • Similar to home manager but for systemd services.
  • Only requires you to run a nix daemon on the target machine.
  • Some limitations, can't use all nixos modules, can't manage users yet, def interesting tho.
  • Interesting spinoff project - numtide/nix-vm-test
    • Use the nix virtual machine test driver to test on other distributions.

my nixos home lab

  • This presenter had a bit of a struggle finding the room, but after he finally arrived he took of flying :D
  • Some nice tips about ways to manage vms with nix
    • using profiles in nixpkgs to spin up various types of vms
    • adding the growPartition option to your guests to allow them to resize automatically
    • Some ideas about structuring your nixos configuration to avoid too many targets when you have a lot of vms.

nixops 4

  • The 3rd iteration of the nixops tool, from the ground up.
  • According to the presenter, nixops 2 could not be saved. :)
  • An ambitious project inspired by terraform that aims to be a declarative way to manage your infrastructure using nix.
  • Not quite ready for production yet, but I'm excited to see where this goes.

Bonus talk:
go in the nix ecosystem

  • didn't see this one live, but it's already online and is a interesting look at the future of packaging go in nixpkgs.

Hachyderm.io Birds Of a Feather

  • My mastodon server
  • A community meetup where they talked about how the infra is setup and how they're developing the project.
  • Great to connect with some of the maintainers and other users, really nice community.

25 years of systemd

  • This was a talk by Pottering about the history of systemd I really wanted to see.
  • Unfortunately the room was already full when I got there a bit late after the previous event :(
  • The rest of the group really enjoyed it tho, so I will watch it once it's online.

Pizza time!

bytenight

  • Hackerspace Brussels had a new location this year, in a cool event space with a industrial feel.
  • Met up with our colleague Victor from embedded there, and we talked for a while with some
    guys from a subsidiary of Bosch who did yocto, and had some interesting talks.

Observability Devroom

Flink with Prometheus

  • I had some hope for this talk, because they're solving a problem we have (high cardinality metrics).
  • However, this is a java project that relies on kafka.
  • Somehow the cure seems worse than the disease.

Prometheus 3.0

  • First release after 7 years.
  • Brand new UI.
  • full unicode support for timeseries names.
  • OpenTelemetry support.
  • Fixes a bunch of defaults. Feature flags

Declarative and Minimalistic Computing

  • Couldn't get into talk about qemu on bsd and darwin, so decided to check out this dev room a bit earlier.
  • There was a utterly uncomprehensible talk about keyboard mapping with Prolog.
  • Then a talk about smallheaded programming, and how zig, prescheme and nim does c transpiling.
  • Finally a talk I really liked by a fellow Norwegian pmunch about nim and his
    project futhark which does automatic wrapping of C headers for nim.

Lightning Lightning Talks

  • Was a fun way to kill an hour, new weird stuff every 5 minutes.
  • The most interesting was probably quickjs-ng - a friendly fork of the quickjs project.
  • There was also a pretty cool talk about how to make your own open source Terrarium.

After that I had about an hour to kill before my flight, so I decided to go check out the booths.

  • All the major Linux flavors was there, and a lot of mobile linux projects like Mobian, SailfishOS and postmarketOS.
  • There was also a gaming section, I really liked Firefly Zero a hand held console that runs web assembly games, including multiplayer, had fun racing another attendee in snake :)
  • I also picked up this fun badge from Fossasia. It's fully open source and communicates over BLE.
  • Met some old friends at the Raku booth, and had a nice chat with the pine64 guys.
    • Their eink tablet can now actually run debian with wayland. They also have a weird risc64 tablet :) https://pine64.org/

Some other talks that are already online

In conclusion: I'll be back next year!

And I hope to see you there too!