Prometheus exporter for certain Docker container metadata metrics

cnexporter uses Go Docker SDK to poll Docker API for a handful of container data.

The exporter publishes several custom metrics via its /metrics endpoint:

• cnexporter_containers_total: Gauge, total number of containers existing on the reporting system;

• cnexporter_containers_running Gauge, number of Docker containers with state running;

• cnexporter_containers_created Gauge, number of containers with state created;

• cnexporter_containers_exited Gauge, number of containers with state exited;

• cnexporter_containers_metadata Gauge, always reports 0. This metric contains the following labels:

  • id
  • image: name of the registry image
  • name: name of the container itself
  • status: e.g. Up 10 days (healthy) (taken directly from the API)
  • state: running, exited, etc.

Also, all metrics expose the nodename label that is set to the reporting system's hostname. This is done to allow matching with node_uname_info metric provided by https://github.com/prometheus/node_exporter, and for other people like me who need this way of querying Prometheus per-node.

I was frustrated with https://github.com/google/cadvisor, how convoluted and bloated it is (I failed to get some of the simple container metadata from it). Also, sadly, https://github.com/prometheus-net/docker_exporter (which provided certain useful container metadata) was decommissioned.

So I decided to write a dead-simple and lightweight tool that would give me the specific overview metrics that I need in my work.

Grab a binary from the Releases page (Linux x86_64/amd64 only).

Alternatively, compile the exporter yourself (you will need at least Go 1.18).

make install

This will put cnexporter under /usr/bin by default (customizable via the PREFIX environment variable).

Or manually call go build main.go, compiling for whatever platform you want.

Just run it in whatever persistent way you prefer. If you want to go the systemd way, there's an example .service file in the repo.

As of now, there are but two options that you can set via CLI (aside from --version):

--port: set a port for publishing the Prometheus exporter metrics (default: 9200);

--timeout: how often the tool will poll Docker API for information, in seconds (default: 15).