Yes, I'm aware of mcuadros/ofelia (~10MB), it was the main inspiration for this project. A great project, don't get me wrong. It was just missing certain key enterprise features I felt were required to support where docker is heading.

Features

Easy to read schedule syntax allowed.
Allows for comments, cause we all need friendly reminders of what update_script.sh actually does.
Start an image using image.
Run command in a container using container.
Run command on a instances of a scaled container using project.
Ability to trigger scripts in other containers on completion cron job using trigger.

Config.json

name: Human readable name that will be used as the job filename. Will be converted into a slug. Optional.
comment: Comments to be included with crontab entry. Optional.
schedule: Crontab schedule syntax as described in https://en.wikipedia.org/wiki/Cron. Ex @hourly, @every 1h30m, * * * * *. Required.
command: Command to be run on in crontab container or docker container/image. Required.
image: Docker images name (ex library/alpine:3.5). Optional.
project: Docker Compose/Swarm project name. Optional, only applies when contain is included.
container: Full container name or container alias if project is set. Ignored if image is included. Optional.
dockerargs: Command line docker run/exec arguments for full control. Defaults to .
trigger: Array of docker-crontab subset objects. Subset includes: image,project,container,command,dockerargs
onstart: Run the command on crontab container start, set to true. Optional, defaults to falsey.

See config.sample.json for examples.

[{
 	"schedule":"@every 5m",
 	"command":"/usr/sbin/logrotate /etc/logrotate.conf"
 },{
 	"comment":"Regenerate Certificate then reload nginx",
 	"schedule":"43 6,18 * * *",
 	"command":"sh -c 'dehydrated --cron --out /etc/ssl --domain ${LE_DOMAIN} --challenge dns-01 --hook dehydrated-dns'",
 	"dockerargs":"--env-file /opt/crontab/env/letsencrypt.env -v webapp_nginx_tls_cert:/etc/ssl -v webapp_nginx_acme_challenge:/var/www/.well-known/acme-challenge",
 	"image":"willfarrell/letsencrypt",
 	"trigger":[{
 		"command":"sh -c '/etc/scripts/make_hpkp ${NGINX_DOMAIN} && /usr/sbin/nginx -t && /usr/sbin/nginx -s reload'",
 		"project":"conduit",
 		"container":"nginx"
 	}],
 	"onstart":true
 }]

How to use

Command Line

docker build -t crontab .
docker run -d \
    -v /var/run/docker.sock:/var/run/docker.sock:ro \
    -v ./env:/opt/env:ro \
    -v /path/to/config/dir:/opt/crontab:rw \
    -v /path/to/logs:/var/log/crontab:rw \
    crontab

Use with docker-compose

Figure out which network name used for your docker-compose containers
- use docker network ls to see existing networks
- if your docker-compose.yml is in my_dir directory, you probably has network my_dir_default
- otherwise read the docker-compose docs
Add dockerargs to your docker-crontab config.json
- use --network NETWORK_NAME to connect new container into docker-compose network
- use --rm --name NAME to use named container
- e.g. "dockerargs": "--network my_dir_default --rm --name my-best-cron-job"

Dockerfile

FROM willfarrell/crontab

COPY config.json ${HOME_DIR}/

Logrotate Dockerfile

FROM willfarrell/crontab

RUN apk add --no-cache logrotate
RUN echo "*/5 *	* * *  /usr/sbin/logrotate /etc/logrotate.conf" >> /etc/crontabs/logrotate
COPY logrotate.conf /etc/logrotate.conf

CMD ["crond", "-f"]

Logging - In Dev

All stdout is captured, formatted, and saved to /var/log/crontab/jobs.log. Set LOG_FILE to /dev/null to disable logging.

example: e6ced859-1563-493b-b1b1-5a190b29e938 2017-06-18T01:27:10+0000 [info] Start Cronjob **map-a-vol** map a volume

grok: CRONTABLOG %{DATA:request_id} %{TIMESTAMP_ISO8601:timestamp} \[%{LOGLEVEL:severity}\] %{GREEDYDATA:message}

TODO

Have ability to auto regenerate crontab on file change (signal HUP?)
Run commands on host machine (w/ --privileged?)
Write tests
Setup TravisCI