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<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><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><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>
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