The bigtruedata/cron Docker image

Table of Contents

• Overview
• Quick Start

Overview

This image provides a simple way of executing task. Therefore it can be used for administration tasks such as automated backups, periodic command execution in a web front-end, and so.

Major features of this image include

• cron syntax to execute commands, and
• local date & time adjustments.

The image is intended to be used along other containers as a sidecar that perform scheduled tasks related to the container is attached to.

This image is based in the Alpine Linux Docker image to avoid generating a image bigger than necessary.

Quick Start

This image is provided to be executed with a little configuration using environment variables. These variables can be divided into two groups:

• TIME_ZONE and TIME_SERVER to configure and adjust the local time of the container, and
• CRON_ENTRY to scheduling the task the container is ought to execute.

Executing a cron task

The image is currently designed to support the execution of a sigle cron task. The specification of the date and time, and the task to be run is specified using the CRON_ENTRY environment variable. More information on how this format is specified can be found on the crontab(5) manual page on Unix systems.

The following command executes the image and schedules every minute a tasks that prints the current date and time of the running container:

docker run --rm --tty --interactive --env "CRON_ENTRY=* * * * * date" bigtruedata/cron

Configuring the local time of the running container

The local time of the container can be localized using the TIME_ZONE environment variable. If not provided, the configured timezone of the container defaults to Alpine's image configuration (Currently UTC).

The following command uses Iran's time zone to configure the container's location:

docker run --rm --tty --interactive --env "TIME_ZONE=Iran" bigtruedata/cron

Adjusting the container's internal clock

When the image is run the entrypoint script synchronizes the local time using a time server. By default, the time server used is pool.ntp.org but it can be overriden using the TIME_SERVER environment variable.

The following command uses the hora.rediris.es time server for time synchornization:

docker run --rm --tty --interactive --env "TIME_SERVER=hora.rediris.es" bigtruedata/cron