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# Prometheus exporters {#module-services-prometheus-exporters}
Prometheus exporters provide metrics for the
[prometheus monitoring system](https://prometheus.io).
## Configuration {#module-services-prometheus-exporters-configuration}
One of the most common exporters is the
[node exporter](https://github.com/prometheus/node_exporter),
it provides hardware and OS metrics from the host it's
running on. The exporter could be configured as follows:
```nix
{
services.prometheus.exporters.node = {
enable = true;
port = 9100;
enabledCollectors = [
"logind"
"systemd"
];
disabledCollectors = [
"textfile"
];
openFirewall = true;
firewallFilter = "-i br0 -p tcp -m tcp --dport 9100";
};
}
```
It should now serve all metrics from the collectors that are explicitly
enabled and the ones that are
[enabled by default](https://github.com/prometheus/node_exporter#enabled-by-default),
via http under `/metrics`. In this
example the firewall should just allow incoming connections to the
exporter's port on the bridge interface `br0` (this would
have to be configured separately of course). For more information about
configuration see `man configuration.nix` or search through
the [available options](https://nixos.org/nixos/options.html#prometheus.exporters).
Prometheus can now be configured to consume the metrics produced by the exporter:
```nix
{
services.prometheus = {
# ...
scrapeConfigs = [
{
job_name = "node";
static_configs = [{
targets = [ "localhost:${toString config.services.prometheus.exporters.node.port}" ];
}];
}
];
# ...
};
}
```
## Adding a new exporter {#module-services-prometheus-exporters-new-exporter}
To add a new exporter, it has to be packaged first (see
`nixpkgs/pkgs/servers/monitoring/prometheus/` for
examples), then a module can be added. The postfix exporter is used in this
example:
- Some default options for all exporters are provided by
`nixpkgs/nixos/modules/services/monitoring/prometheus/exporters.nix`:
- `enable`
- `port`
- `listenAddress`
- `extraFlags`
- `openFirewall`
- `firewallFilter`
- `firewallRules`
- `user`
- `group`
- As there is already a package available, the module can now be added. This
is accomplished by adding a new file to the
`nixos/modules/services/monitoring/prometheus/exporters/`
directory, which will be called postfix.nix and contains all exporter
specific options and configuration:
```nix
# nixpkgs/nixos/modules/services/prometheus/exporters/postfix.nix
{ config, lib, pkgs, options }:
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 configuration.
# Note that by default 'DynamicUser' is 'true'.
serviceOpts = {
serviceConfig = {
DynamicUser = false;
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}
'';
};
};
}
```
- 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:
`nixpkgs/nixos/modules/services/prometheus/exporters.nix`
## Updating an exporter module {#module-services-prometheus-exporters-update-exporter-module}
Should an exporter option change at some point, it is possible to add
information about the change to the exporter definition similar to
`nixpkgs/nixos/modules/rename.nix`:
```nix
{ config, lib, pkgs, options }:
with lib;
let
cfg = config.services.prometheus.exporters.nginx;
in
{
port = 9113;
extraOpts = {
# additional module options
# ...
};
serviceOpts = {
# service configuration
# ...
};
imports = [
# 'services.prometheus.exporters.nginx.telemetryEndpoint' -> 'services.prometheus.exporters.nginx.telemetryPath'
(mkRenamedOptionModule [ "telemetryEndpoint" ] [ "telemetryPath" ])
# removed option 'services.prometheus.exporters.nginx.insecure'
(mkRemovedOptionModule [ "insecure" ] ''
This option was replaced by 'prometheus.exporters.nginx.sslVerify' which defaults to true.
'')
({ options.warnings = options.warnings; })
];
}
```
|