Docker Cron

register cron jobs in docker labels.

• jobs schedule have second precision (not minutes like old standard crontabs)
• jobs command are executed in the container itself
• can export metrics to influxdb for monitoring

exemple:

- "cron.test.schedule=* * * * * *"
- "cron.test.command=echo hi"
- "cron.test.no-overlap=true"
- "cron.test.timeout=5"
- "cron.test.user=www-data"

Install

Execute this line to download dockercron

git clone https://github.com/rafipiccolo/dockercron.git dockercron

Create a docker-compose.yml

version: "3.3"
services:
    datelogger:
        image: busybox
        container_name: datelogger
        command: sh -c "while true; do id; sleep 1; done"
        restart: always
        labels:
            - "cron.test.schedule=* * * * * *"
            - "cron.test.command=sleep 2 && echo soak && sleep 2 && echo soak2 && sleep 2 && echo soak3"
            - "cron.test.timeout=5"
            - "cron.test.no-overlap=true"

    dockercron:
        build: ./dockercron
        container_name: dockercron
        restart: always
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock:ro
        environment:
            - "INFLUXDB=http://influxdb:8086/write?db=dockercron"
            - "VERBOSE=true"
        labels:
            - traefik.enable=true
            - traefik.http.routers.dockercron.rule=Host(`dockercron.${DOMAIN}`)
            - traefik.http.routers.dockercron.tls.certresolver=le
            - traefik.http.routers.dockercron.entrypoints=websecure
            - traefik.http.routers.dockercron.middlewares=securityheaders,admin
        healthcheck:
            test: ['CMD', 'curl', '-f', 'http://localhost:3000/health']

The job called "test" will execute the command "echo hi" every second.

start it

docker compose up -d

Update

cd dockercron
git pull
cd ..
docker compose build dockercron
docker compose up -d dockercron

Config

environment variables :

• INFLUXDB : (optional)

  The influxdb url used to push data. exemple of url : http://influxdb:8086/write?db=dockercron exemple of data written to influxdb : dockercron,cronname=test ms=246.950014,exitCode=0 1588797072250000000

• VERBOSE : (optional) (default 0)

  set 1 or true to see debug informations

• HOSTNAME : the hostname tag pushed to influxdb

labels format :

- "cron.{cronname}.{option}={value}"

command

- "cron.test.command=echo hi" :
# to execute the cron command we use sh -c command
# the command is executed on the docker container itself
# so "sh" and the other binaries you want to use must exist in the container.

schedule

- "cron.test.schedule=* * * * * *"
# jobs schedule have second precision

no-overlap

- "cron.test.no-overlap=true"
# prevent a job to start again if already running

timeout

- "cron.test.timeout=5"
# kill the job if timeout is reached (seconds)

user - "cron.test.user=www-data" # run the job as this user, inside the container (default root)

available routes

• /
• /state
• /state/:id
• /state/:id/:name
• /health

How it works

On startup we call docker to get all running containers labels and then we register the cronjobs we found

In parralel we poll docker events :

• everytime a container is "die" / "stop" => remove all cronjobs of this container
• everytime a container is "start" => remove and then register all cronjobs of this container

This package is used to parse and execute cron jobs : https://www.npmjs.com/package/cron This package is used to communicate with docker : https://www.npmjs.com/package/dockerode