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Local peer to peer binary cache with NixOS and Peerix

Written by Solène, on 25 August 2022.
Tags: #nixos

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Introduction §

There is a cool project related to NixOS, called Peerix. It's a local daemon exposed as a local substituter (a server providing binary packages) that will discover other Peerix daemon on the local network, and use them as a source of binary packages.

Peerix is a simple way to reuse package already installed somewhere on the network instead of downloading it again. Packages delivered by Peerix substituters are signed with a private key, so you need to import each computer public key before being able to download/use their packages. While this can be cumbersome, this also mandatory to prevent someone on the network to spoof packages.

Perrix should be used wisely, because secrets in your store could be leaked to others.

Peerix GitHub page

Generating the keys §

First step is to generate a pair of keys for each computer using Peerix.

In the directory in which you have your configurations files, use the command:

nix-store --generate-binary-cache-key "peerix-$(hostname -s)" peerix-private peerix-public

Setup §

I will only cover the flakes installation on NixOS. Add the files peerix-private and peerix-public to git as this is a requirement to flakes.

NOTE: if you find a way to not add the private key to the store, I'll be glad to hear about your solution!

Add this input in your flake.nix file:

  peerix = {
    url = "github:cid-chan/peerix";
    inputs.nixpkgs.follows = "nixpkgs";
  };

Add "nixos-hardware" in the outputs parameters lile:

outputs = { eslf, nixpkgs, nixos-hardware}: {

And in the modules list of your configuration, add this:

  peerix.nixosModules.peerix
  {
    services.peerix = {
      enable = true;
      package = peerix.packages.x86_64-linux.peerix;
      openFirewall = true; # UDP/12304
      privateKeyFile = ./peerix-private;
      publicKeyFile =  ./peerix-public;
      publicKey = "THE CONTENT OF peerix-public FROM THE OTHER COMPUTER";
      # example # publicKey = "peerix-laptop:1ZjzxYFhzeRMni4CyK2uKHjgo6xy0=";
    };
  }

If you have multiple public keys to use, just add them with a space between each value.

Run "nix flake lock --update-input peerix" and you can now reconfigure your system.

How to use §

There is nothing special to do, when you update your system, or use nix-shell, the nix-daemon will use the local Peerix substituter first which will discover other Peerix instances if any, and will use them when possible.

You can check the logs of the peerix daemons using "journalctl -f -u peerix.service" on both systems.

Conclusion §

While Peerix isn't a big project, it has a lot of potential to help NixOS users with multiple computers to have a more efficient bandwidth usage, but also build time. If you build the same project (with same inputs) on your computers, you can pull the result from the other.