nixpkgs/nixos/modules/services/monitoring/prometheus/exporters.xml

<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         version="5.0"
         xml:id="module-services-prometheus-exporters">
 <title>Prometheus exporters</title>
 <para>
  Prometheus exporters provide metrics for the
  <link xlink:href="https://prometheus.io">prometheus monitoring system</link>.
 </para>
 <section xml:id="module-services-prometheus-exporters-configuration">
  <title>Configuration</title>

  <para>
   One of the most common exporters is the
   <link xlink:href="https://github.com/prometheus/node_exporter">node
   exporter</link>, it provides hardware and OS metrics from the host it's
   running on. The exporter could be configured as follows:
<programlisting>
  services.promtheus.exporters.node = {
    enable = true;
    enabledCollectors = [
      "logind"
      "systemd"
    ];
    disabledCollectors = [
      "textfile"
    ];
    openFirewall = true;
    firewallFilter = "-i br0 -p tcp -m tcp --dport 9100";
  };
</programlisting>
   It should now serve all metrics from the collectors that are explicitly
   enabled and the ones that are
   <link xlink:href="https://github.com/prometheus/node_exporter#enabled-by-default">enabled
   by default</link>, via http under <literal>/metrics</literal>. In this
   example the firewall should just allow incoming connections to the
   exporter's port on the bridge interface <literal>br0</literal> (this would
   have to be configured seperately of course). For more information about
   configuration see <literal>man configuration.nix</literal> or search through
   the
   <link xlink:href="https://nixos.org/nixos/options.html#prometheus.exporters">available
   options</link>.
  </para>
 </section>
 <section xml:id="module-services-prometheus-exporters-new-exporter">
  <title>Adding a new exporter</title>

  <para>
   To add a new exporter, it has to be packaged first (see
   <literal>nixpkgs/pkgs/servers/monitoring/prometheus/</literal> for
   examples), then a module can be added. The postfix exporter is used in this
   example:
  </para>

  <itemizedlist>
   <listitem>
    <para>
     Some default options for all exporters are provided by
     <literal>nixpkgs/nixos/modules/services/monitoring/prometheus/exporters.nix</literal>:
    </para>
   </listitem>
   <listitem override='none'>
    <itemizedlist>
     <listitem>
      <para>
       <literal>enable</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>port</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>listenAddress</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>extraFlags</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>openFirewall</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>firewallFilter</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>user</literal>
      </para>
     </listitem>
     <listitem>
      <para>
       <literal>group</literal>
      </para>
     </listitem>
    </itemizedlist>
   </listitem>
   <listitem>
    <para>
     As there is already a package available, the module can now be added. This
     is accomplished by adding a new file to the
     <literal>nixos/modules/services/monitoring/prometheus/exporters/</literal>
     directory, which will be called postfix.nix and contains all exporter
     specific options and configuration:
<programlisting>
        # nixpgs/nixos/modules/services/prometheus/exporters/postfix.nix
        { config, lib, pkgs }:

        with lib;

        let
          # for convenience we define cfg here
          cfg = config.services.prometheus.exporters.postfix;
        in
        {
          port = 9154; # The postfix exporter listens on this port by default

          # `extraOpts` is an attribute set which contains additional options
          # (and optional overrides for default options).
          # Note that this attribute is optional.
          extraOpts = {
            telemetryPath = mkOption {
              type = types.str;
              default = "/metrics";
              description = ''
                Path under which to expose metrics.
              '';
            };
            logfilePath = mkOption {
              type = types.path;
              default = /var/log/postfix_exporter_input.log;
              example = /var/log/mail.log;
              description = ''
                Path where Postfix writes log entries.
                This file will be truncated by this exporter!
              '';
            };
            showqPath = mkOption {
              type = types.path;
              default = /var/spool/postfix/public/showq;
              example = /var/lib/postfix/queue/public/showq;
              description = ''
                Path at which Postfix places its showq socket.
              '';
            };
          };

          # `serviceOpts` is an attribute set which contains configuration
          # for the exporter's systemd service. One of
          # `serviceOpts.script` and `serviceOpts.serviceConfig.ExecStart`
          # has to be specified here. This will be merged with the default
          # service confiuration.
          serviceOpts = {
            serviceConfig = {
              ExecStart = ''
                ${pkgs.prometheus-postfix-exporter}/bin/postfix_exporter \
                  --web.listen-address ${cfg.listenAddress}:${toString cfg.port} \
                  --web.telemetry-path ${cfg.telemetryPath} \
                  ${concatStringsSep " \\\n  " cfg.extraFlags}
              '';
            };
          };
        }
      </programlisting>
    </para>
   </listitem>
   <listitem>
    <para>
     This should already be enough for the postfix exporter. Additionally one
     could now add assertions and conditional default values. This can be done
     in the 'meta-module' that combines all exporter definitions and generates
     the submodules:
     <literal>nixpkgs/nixos/modules/services/prometheus/exporters.nix</literal>
    </para>
   </listitem>
  </itemizedlist>
 </section>
</chapter>