services.prometheus: refactor to modular prometheus exporters

[milahu]

currently im trying to add services.prometheus.exporters.qbittorrent
to fix Package request: prometheus-qbittorrent-exporter

actual

this requires
adding nixos/modules/services/monitoring/prometheus/exporters/qbittorrent.nix
patching nixos/modules/services/monitoring/prometheus/exporters.nix
disabling the module services/monitoring/prometheus/default.nix
importing prometheus/default.nix from the patched nixpkgs

{ config, pkgs, lib, modulesPath, inputs, ... }:

{
  # override nixos modules
  # https://stackoverflow.com/a/46407944/10440128
  # see also: nixos/modules/module-list.nix
  disabledModules = [

    # no. error: The option `services.prometheus.exporters.qbittorrent' does not exist.
    # override services.prometheus
    #"services/monitoring/prometheus/default.nix"

    # override services.prometheus.exporters
    "services/monitoring/prometheus/exporters.nix"
  ];

  imports = [
    ./hardware-configuration.nix

    # no. error: The option `services.prometheus.exporters.qbittorrent' does not exist.
    # override services.prometheus
    #./modules/services/monitoring/prometheus/default.nix

    # override services.prometheus.exporters
    ./modules/services/monitoring/prometheus/exporters.nix
  ];

expected

ideally this should work without patching prometheus/exporters.nix
only by adding prometheus/exporters/qbittorrent.nix to imports

/etc/nixos/configuration.nix

{ config, pkgs, lib, modulesPath, inputs, ... }:

{
  imports = [
    ./hardware-configuration.nix

    # TODO implement modular prometheus exporters
    # add services.prometheus.exporters.qbittorrent
    ./modules/services/monitoring/prometheus/exporters/qbittorrent.nix
  ];

  services.grafana = {
    enable = true;
    declarativePlugins = with pkgs.grafanaPlugins; [
      grafana-piechart-panel # for prometheus-qbittorrent-exporter
    ];
    settings = {
      # ...
    };
  };

  services.prometheus = {
    enable = true;
    port = 9001;
    # /var/lib/prometheus2/
    #retentionTime = "15d"; # default -> 80 MB
    retentionTime = "740d"; # 2 years -> 4 GB
    exporters = {
      node = {
        enable = true;
        enabledCollectors = [ "systemd" ];
        port = 9002;
      };
      qbittorrent = {
        enable = true;
        port = 9003;
        qbittorrentPort = 1952;
        package = pkgs.nur.repos.milahu.prometheus-qbittorrent-exporter;
      };
    };
    scrapeConfigs = [
      {
        job_name = "chrysalis";
        static_configs = [{
          targets = [
            "127.0.0.1:${toString config.services.prometheus.exporters.node.port}"
            "127.0.0.1:${toString config.services.prometheus.exporters.qbittorrent.port}"
          ];
        }];
      }
    ];
  };

possible solution

add a mkPrometheusExporter function
so prometheus/exporters/qbittorrent.nix looks like

{ lib
, mkPrometheusExporter
}:

mkPrometheusExporter {
  name = "qbittorrent";
  # ...
}

probably this would require
adding all prometheus exporters to nixos/modules/module-list.nix

keywords

• decentralization of nixpkgs
• modularization of nixpkgs