Publish a service with Avahi on NixOS

Usually I would create a new .service file and fill in the service details there. But for now I was just able to figure out how to broadcast the hostname and IP address of the server the NixOS way.

I should later find out how to publish a HTTP web service listening on a specific port. This post will in that case be updated. Until then – this will suffice!

Configuration

Open up the main NixOS configuration file at /etc/nixos/configuration.nix and enable the avahi service:

# Publish this server and its address on the network
services.avahi = {
  enable = true;
  publish = {
    enable = true;
    addresses = true;
    workstation = true;
  };
};

Rebuild NixOS

# nixos-rebuild switch --fast

Now, on my other machine, I can see the server broadcasting itself

# systemctl start avahi-daemon.service
$ avahi-browse -park | grep nix
+;wlp3s0;IPv4;nix\032\09100\05830\05818\058a8\058e9\05850\093;_workstation._tcp;local
=;wlp3s0;IPv4;nix\032\09100\05830\05818\058a8\058e9\05850\093;_workstation._tcp;local;nix.local;192.168.0.2;9;

Troubleshooting

Debug mDNS traffic using tcpdump

# tcpdump -ni wlp3s0 port 5353

References

• https://jarmac.org/category/nixos.html
• https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/networking/avahi-daemon.nix
• https://wiki.archlinux.org/index.php/Avahi#Adding_services