Docker Cron

A lightweight Docker image based on Alpine Linux for running cron jobs and startup commands with automatic log rotation.

Features

• Based on Alpine Linux 3.18
• Runs cron jobs defined through environment variables
• Executes startup commands
• Automatic log rotation using logrotate
• Real-time log output

Usage

Running the container

docker run -d \
-e CRON_JOB_EXAMPLE1="* * * * * echo 'Hello, World!'" \
-e CRON_JOB_EXAMPLE2="0 2 * * * echo 'Hourly task'" \
-e STARTUP_COMMAND_EXAMPLE1="echo 'Container started!'" \
-e STARTUP_COMMAND_EXAMPLE2="echo 'Initializing services...'" \
-e STARTUP_CONDITION="curl -s http://localhost:3000" \
monlor/docker-cron:main

Environment Variables

• CRON_JOB_<name>: Define cron jobs. Format: "<schedule> <command>"
• STARTUP_COMMAND_<name>: Define commands to run at container startup
• STARTUP_CONDITION: Define a condition that must be met before starting services

Cron Jobs

Cron jobs are added to the container's crontab. The format is:

RON_JOB_<name>="<schedule> <command>"

Example:

CRON_JOB_HELLO="* * * * * echo 'Hello, World!'"
CRON_JOB_BACKUP="0 2 * * * curl -sSf https://example.com/api/backup"

Startup Commands

Startup commands are executed at container startup. The format is:

STARTUP_COMMAND_<name>="<command>"

Example:

STARTUP_COMMAND_INIT="echo 'Initializing...'"
STARTUP_COMMAND_CONFIG="curl -sSf https://example.com/api/config"

Startup Condition

You can set a startup condition that must be met before the container starts its services. This is useful for ensuring dependencies are ready. The format is:

STARTUP_CONDITION="<command>"

Example:

STARTUP_CONDITION="curl -sSf https://example.com/api/health &> /dev/null"

Log Management

• Logs are stored in /var/log/cron/ and /var/log/
• Log rotation is configured to:
  • Rotate files when they reach 10MB
  • Keep 5 rotated log files
  • Compress old log files

Building the Image

To build the Docker image:

docker build -t your-image-name .

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is open source and available under the MIT License.