harmonia

Harmonia is a binary cache for nix that serves your /nix/store as a binary cache over http. It's written in Rust for speed.

Features

• http-ranges support for nar file streaming
• streaming build logs
• .ls file streaming
  • Note: doesn't contain narOffset in json response but isn't needed for nix-index
• Add /serve/<narhash>/ endpoint to allow serving the content of package. Also discovers index.html to allow serving websites directly from the nix store.
• Content is compressed transparently with zstd.
• Builtin TLS: when no frontend webserver is used, Harmonia can also provide TLS encryption

Configuration for public binary cache on NixOS

There is a module for harmonia in nixpkgs. The following example set's up harmonia as a public binary cache using nginx as a frontend webserver with https encryption:

{ config, pkgs, ... }: {
  services.harmonia.enable = true;
  # FIXME: generate a public/private key pair like this:
  # $ nix-store --generate-binary-cache-key cache.yourdomain.tld-1 /var/lib/secrets/harmonia.secret /var/lib/secrets/harmonia.pub
  services.harmonia.signKeyPaths = [ "/var/lib/secrets/harmonia.secret" ];
  # Example using sops-nix to store the signing key
  #services.harmonia.signKeyPaths = [ config.sops.secrets.harmonia-key.path ];
  #sops.secrets.harmonia-key = { };

  # optional if you use allowed-users in other places
  #nix.settings.allowed-users = [ "harmonia" ];

  networking.firewall.allowedTCPPorts = [ 443 80 ];

  # FIXME: replace this with your own email
  security.acme.defaults.email = "[email protected]";
  security.acme.acceptTerms = true;

  services.nginx = {
    enable = true;
    recommendedTlsSettings = true;
    # FIXME: replace "cache.yourdomain.tld" with your own domain.
    virtualHosts."cache.yourdomain.tld" = {
      enableACME = true;
      forceSSL = true;

      locations."/".extraConfig = ''
        proxy_pass http://127.0.0.1:5000;
        proxy_set_header Host $host;
        proxy_redirect http:// https://;
        proxy_http_version 1.1;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;
      '';
    };
  };
}

You can use the binary cache on a different machine using the following NixOS configuration:

{
  nix.settings = {
    substituters = [ "https://cache.yourdomain.tld" ];
    # FIXME replace the key with the content of /var/lib/secrets/harmonia.pub
    trusted-public-keys = [ "cache.yourdomain.tld-1:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=" ];
  };
}

Configuration format

Configuration is done via a toml file. Hint: You don't need to interface with the configuration directly in case you are using the NixOS module. The location of the configuration file should be passed as env var CONFIG_FILE. If no config file is passed the following default values will be used:

# default ip:hostname to bind to
bind = "[::]:5000"
# unix socket are also supported
# bind = "unix:/run/harmonia/socket"
# Sets number of workers to start in the webserver
workers = 4
# Sets the per-worker maximum number of concurrent connections.
max_connection_rate = 256
# binary cache priority that is advertised in /nix-cache-info
priority = 30

# Allow to override the store path advertised in /nix-cache-info
# virtual_nix_store = "/nix/store"
# Allow to serve the nix store from a different physical location
# Default: empty
# Example: if you use `nix copy --store /guest` to populate a store than configure:
# real_nix_store = "/guest/nix/store"

Per default we wont sign any narinfo because we don't have a secret key, to enable this feature enable it by providing a path to a private key generated by nix-store --generate-binary-cache-key cache.example.com-1 /etc/nix/cache.secret /etc/nix/cache.pub

# nix binary cache signing key
sign_key_paths = [ "/run/secrets/cache.secret" ]

Harmonia also reads the SIGN_KEY_PATHS environment variable which holds paths to secret keys separated by spaces. All paths provided by sign_key_paths config option and SIGN_KEY_PATHS environment variable will be used for signing.

Logging can be configured with env_logger. The default value is info,actix_web=debug. To only log errors use the following RUST_LOG=error and to only disable access logging, use RUST_LOG=info,actix_web::middleware=error

To enable TLS on the HTTP server, specify tls_cert_path and tls_key_path.

Build

Whole application

nix build -L

Get a development environment:

nix develop

Run tests

nix flake check -L

Inspiration

• eris