Fedimint Observer

Fedimint Observer is intended to become the "mempool.space for Fedimint". Due to the privacy properties of Fedimint it won't be able to show concrete transaction flows, but transfers in and out of single federations are visible. By making clear to users what is and isn't visible I hope to make Fedimint more transparent and thus more trustworthy. Furthermore, I hope that it can inform developer decisions around improving privacy by having access to easily queryable federation data to quantify possible privacy improvements.

Currently, Fedimint Observer consists of two sub-APIs:

Federation Observer

This is likely the component that most people are actively exposed to. It is a server application that scans a list of federations for their publicly available data (session log, announcements, …) and writes the data to a postgres database. The data is then exposed via a REST API.

These APIs live under the /federations path, you can find all the endpoints in fmo_server/src/federation/mod.rs. One example is the /federations endpoint itself that returns a list of all federations that are being observed.

This API is also the data source for the fontend that powers https://observer.fedimint.org and is also hosted in this repository in the fmo_frontend directory. The frontend is a Leptos PWA, so is fully written in Rust and compiled to WASM. It uses Tailwind and Flowbite for styling.

When it comes to stability guarantees the Postgres database should always be migratable backwards-compatibly, so we don't lose historic data. The API under /federations isn't stable at this point and I'd recommend to subscribing to changes in Fedimint Observer if building against it.

Federation Inspector

The lesser-known component is an API under the /config path it can be used to get a JSON-encoded version of the federation config if you have an invite code. The first time it fetches the config from the federation using the invite code, after that it will return a version cached in memory (till the service is restarted). The endpoints can be found in fmo_server/src/config/mod.rs.

This service is already used by bitcoinmints.com and can thus be considered kinda stable.

Development

Fedimint Observer comes with a nix development environment. You can enter it by running nix develop. In there you can run a variety of just commands (to be called as just <COMMAND> <ARGS...>), the most important ones are:

• check: run cargo check on the entire workspace
• pg_start and pg_stop: start/stop a postgresql instance for local testing in the background
• pg_backup and pg_restore: in case you are building a DB migration it's useful to be able to reset the DB
• serve_frontend: automatically rebuild the frontend on changes and serve it with trunk

Deployment

I currently run the public instance at https://observer.fedimint.org using the following nix config:

{ lib, pkgs, fedimint-observer, system, ... }: let
   fmo = fedimint-observer.packages."${system}";
 in {
  systemd.services.fedimint-observer = {
    enable = true;
    wantedBy = [ "multi-user.target" ];
    environment = {
      FO_BIND = "127.0.0.1:5000";
      FO_DATABASE = "postgresql:///fmo?user=fmo";
      # Set to your admin password, used to add federations to be observed via curl
      FO_ADMIN_AUTH = ;
      ALLOW_CONFIG_CORS = "true";
    };
    serviceConfig = {
      ExecStart = ''
        ${fmo.fmo_server}/bin/fmo_server
      '';
      User = "fmo";
      Group = "fmo";
      Restart = "always";
      RestartSec = "10s";
    };
  };

  services.postgresql = {
    enable = true;
    ensureDatabases = [ "fmo" ];
    ensureUsers = [
      { name = "fmo"; }
    ];
    initialScript = pkgs.writeText "backend-initScript" ''
      GRANT ALL PRIVILEGES ON DATABASE fmo TO fmo;
      \c fmo
      GRANT ALL ON SCHEMA public TO fmo;
    '';
  };

  services.nginx = {
    enable = true;
    virtualHosts."observer.fedimint.org" = {
      enableACME = true;
      forceSSL = true;
      root = fmo.fmo_frontend;
      locations."/" = {
        extraConfig = ''
          try_files $uri $uri/ /index.html;
        '';
      };
      locations."/api/" = {
        proxyPass = "http://127.0.0.1:5000/";
      };
    };
  };

  users.users."fmo" = {
    isSystemUser = true;
    group = "fmo";
  };
  users.groups."fmo" = {};
}