docker-crontab

A simple wrapper over docker to all complex cron job to be run in other containers.

Supported tags and Dockerfile links

• latest (Dockerfile)
• 1.0.0 (Dockerfile)
• 0.6.0 (Dockerfile)

Why?

Yes, I'm aware of mcuadros/ofelia (>250MB when this was created), 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 file

The config file can be specifed in any of json, toml, or yaml, and can be defined as either an array or mapping (top-level keys will be ignored; can be useful for organizing commands)

• 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-samples 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

1. 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
2. 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