docker

The docker plugin reports every container on the host, running or stopped, grouped by compose project. It sends state, health, CPU, memory, restart count and network and disk I/O rates per container. Turn it on for any host that runs Docker or Podman.

Enable it

Add docker to the plugins array.

{
  "plugins": ["docker"],
  "docker": {
    "refreshInterval": 60000,
    "dockerBin": "docker",
    "projects": [],
    "exclude": []
  }
}

Option	Default	What it does
refreshInterval	60000	Milliseconds between reports. The plugin sends one report at startup, then one per interval.
dockerBin	"docker"	The CLI to run. bin is accepted as an alias. Set it to podman for Podman.
projects	[]	If set, report only these compose projects.
exclude	[]	Compose projects to skip.

projects and exclude match the compose project name. A container started without compose is its own group, named after the container, so you filter it by container name.

What it reports

One payload per compose project, with unique id docker-<project>.

• project, host (the machine hostname), engine: "docker", running and total counts.
• containers, one entry per container:
  • name, service (the compose service name), image, state, status (Docker's text, such as Up 2 days (healthy)), running.
  • health is healthy, unhealthy, starting or empty, parsed from the status text.
  • cpu in percent of one core, mem and memLimit in bytes, memPercent.
  • restarts and exitCode from docker inspect.
  • netIn, netOut, blkRead, blkWrite in bytes per second. These appear from the second report on.
  • For up to five unhealthy containers, healthOutput (the last failing healthcheck's output, with curl's progress meter stripped), healthFailingStreak and healthExitCode.

I/O rates come from the kernel where possible, from /proc/<pid>/net/dev and the cgroup v2 io.stat. If those can't be read, the plugin falls back to docker stats, which rounds to three significant figures. A container on host networking reports zero network traffic.

When it alerts

Condition	Severity
Any container has health = unhealthy	error
Any container is stopped with a non-zero exitCode	error
Any container is stopped with exit code 0	warning

The reason names up to two containers and counts the rest, for example web: api unhealthy after 3 failed checks: curl: (7) Failed to connect. A healthcheck exit code of -1 reads as healthcheck timed out. More than two restarts adds , N restarts.

A new problem does not notify on the first bad report. The server holds it until a second consecutive report from the same project is still bad. When the project reports clean again, the server resolves the alert.

Clustered services

If a cluster rule names this project, the cluster judges it across its member hosts instead.

• A rule with no container name hands the whole project to the cluster. The host sends no alert for it.
• A rule with match_container removes only those compose services from this host's check. The other containers in the project still alert as normal.

On the dashboard

One card per compose project, labelled Docker · <host>, with one unit per container.

Reading	Source	Warn	Crit
RUNNING	running/total	fewer running than total	none
CPU	sum of container cpu, shown in cores	above 2 cores	above 3 cores
MEM	sum of container mem	none	none
NET	sum of netIn + netOut	none	none
DISK I/O	sum of blkRead + blkWrite	none	none

Each container unit is red when unhealthy or stopped with a non-zero exit code, and amber when stopped cleanly or when its health is starting. Containers that are not green also appear in the card's event list, up to eight.

CPU pressure raises the card color for display only. A project that has not reported for 300 seconds shows OFFLINE. A clustered project that is not placed on this host shows STANDBY · <cluster>.

Requirements

• The docker (or podman) CLI on the PATH, or a full path in dockerBin.
• The agent user must be able to reach the engine. For Docker that means root or membership in the docker group.
• Exact I/O counters need read access to /proc/<pid> and /sys/fs/cgroup, on cgroup v2. Without them the plugin uses the rounded docker stats figures.

Gotchas

• The plugin checks for the engine once, at startup. If the engine is not up yet, the plugin stays idle until the agent restarts.
• A stopped container with exit code 0 is a warning, not silence. Remove one-shot containers or exclude their project if they exit by design.