docker-alpine-cron

Dockerfile and scripts for creating image with Cron based on Alpine
Installed packages: dcron wget rsync ca-certificates

Usage

Environment variables:

CRON_STRINGS - strings with cron jobs. Use "\n" for newline (Default: undefined)
CRON_TAIL - if defined the cron log file will be sent to stdout by tail. Additionally, if set to the value no_logfile, no log file will be created and logging will be to stdout only. (Default: undefined)
CRON_CMD_OUTPUT_LOG - if defined the output of the commands executed by cron will also be sent to stdout, otherwise they will be ignored (Default: undefined)

crond always runs in the foreground

Cron files

• /etc/cron.d - place to mount custom crontab files

When image runs, files in /etc/cron.d will copied to /var/spool/cron/crontab.
If CRON_STRINGS defined script creates file /var/spool/cron/crontab/CRON_STRINGS

Log files

Unless CRON_TAIL is set to no_logfile, the log file will be placed in /var/log/cron/cron.log.

Simple usage:

docker run --name="alpine-cron-sample" -d \
-v /path/to/app/conf/crontabs:/etc/cron.d \
-v /path/to/app/scripts:/scripts \
actyx/docker-alpine-cron

With scripts and CRON_STRINGS

docker run --name="alpine-cron-sample" -d \
-e 'CRON_STRINGS=* * * * * /scripts/myapp-script.sh'
-v /path/to/app/scripts:/scripts \
actyx/docker-alpine-cron

Get URL by cron every minute

docker run --name="alpine-cron-sample" -d \
-e 'CRON_STRINGS=* * * * * wget --spider https://sample.dockerhost/cron-jobs'
actyx/docker-alpine-cron

Building

actyx/docker-alpine-cron:latest is a multi-platform image. To properly create it you need to use buildx and QEMU:

docker buildx build --tag actyx/docker-alpine-cron:armv6 --platform linux/arm/v6 --push .
docker buildx build --tag actyx/docker-alpine-cron:armv7 --platform linux/arm/v7 --push .
docker buildx build --tag actyx/docker-alpine-cron:amd64 --platform linux/amd64 --push .
docker manifest create actyx/docker-alpine-cron:latest actyx/docker-alpine-cron:amd64 actyx/docker-alpine-cron:armv6 actyx/docker-alpine-cron:armv7
docker manifest push actyx/docker-alpine-cron:latest

The docker manifest create needs to be done only once.