digineo / postfix_exporter

A Prometheus exporter for Postfix.

Note: This is a fork of kumina/postfix_exporter with experimental changes to support multiple Postfix instances.

This code base introduces a large number breaking changes compared to kumina/postfix_exporter, not only code itself, but also in the exported metrics.

Prometheus Postfix exporter

Prometheus metrics exporter for the Postfix mail server. This exporter provides histogram metrics for the size and age of messages stored in the mail queue. It extracts these metrics from Postfix by connecting to a UNIX socket under /var/spool. It also counts events by parsing Postfix's log entries, using regular expression matching. The log entries are retrieved from the systemd journal, the Docker logs, or from a log file.

Options

These options can be used when starting the postfix_exporter

Flag	Description	Default
--web.listen-address	Address to listen on for web interface and telemetry	9154
--web.telemetry-path	Path under which to expose metrics	/metrics
--postfix.instance	Name of Postfix instances to monitor (option can be repeated)	postfix
--log.source	Define log source (supports file, docker, systemd)	file
--log.unsupported	Log all unsupported lines	false
--logfile.path	Path where Postfix writes log entries	/var/log/mail.log
--docker.container.id	The container to read Docker logs from	postfix
--systemd.unit	Name of the Postfix systemd unit	[email protected]
--systemd.slice	Name of the Postfix systemd slice (overrides --systemd-unit)	(empty)
--systemd.journal_path	Path to the systemd journal	(empty)

Notes:

• depending the value of --log.source, only a subset of options is evalutated:
  • for file: --logfile.path
  • for docker: --docker.container.id
  • for systemd: --systemd.journal_path, and either --systemd.unit or --systemd.slice

Multiple Postfix instances

It is possible to monitor multiple Postfix instances at the same time, however currently some restrictions need to be met:

Firstly, the instance names must directy match the $queue_directory and $syslog_name, i.e. instance postfix-foo queues to /var/spool/postfix-foo and creates logs with postfix-foo/ prefix.

This is accomblished by setting at least the following in the instances main.cf:

multi_instance_name = postfix-strict
queue_directory     = /var/spool/postfix-strict

Secondly, if you use systemd, you need to start the exporter with --systemd.slice, as --systemd.unit only accepts a single unit name.

For Ubuntu 20.04, a multi-instance setup may look like this:

./postfix_exporter \
        --log.source systemd \
        --systemd.instance postfix \
        --systemd.instance postfix-secondary \
        --systemd.slice system-postfix.slice

Events from Docker

Postfix servers running in a Docker container can be monitored using the --log.source=docker flag. The default container ID is postfix, but can be customized with the --docker.container.id flag.

The default is to connect to the local Docker, but this can be customized using the DOCKER_HOST and similar environment variables.

Events from log file

The log file is tailed when processed. Rotating the log files while the exporter is running is OK. The path to the log file is specified with the --postfix.logfile_path flag, and must be enabled with --log.source=file.

Events from systemd

Retrieval from the systemd journal is enabled with --log.source=systemd. It is possible to specify the unit (with --systemd.unit) or slice (with --systemd.slice). Additionally, it is possible to read the journal from a directory with the --systemd.journal_path flag.

Build options

Default the exporter is build with systemd journal functionality (but it is disabled at default). Because the systemd headers are required for building with systemd, there is an option to build the exporter without systemd. Use the build tag nosystemd.

go build -tags nosystemd