Harmonia

harmonia is a small utility to serve a Nix store as a binary cache, allowing it to be used as a substituter by other Nix installations.

Setup

First generate required public and private store keys, in this example for the domain cache.example.org.

mkdir -p /var/lib/harmonia
nix-store --generate-binary-cache-key cache.example.org-1 \
  /var/lib/harmonia/cache-priv-key.pem \
  /var/lib/harmonia/cache-pub-key.pem

Add following snippet to your system configuration and apply it.

services.harmonia = {
  enable = true;
  signKeyPaths = [ "/var/lib/harmonia/cache-priv-key.pem" ];
};

The cache will be served on http://127.0.0.1:5000. It should be served with a web server such as Caddy.

services.caddy = {
  enable = true;
  openFirewall = true;
  virtualHosts."cache.example.org".extraConfig = ''
    reverse_proxy 127.0.0.1:5000
  '';
};

Visit https://cache.example.org where you'll also find instructions on how to setup the cache on a client.