Crooner

A small utility written in Rust that allows scheduling Docker commands to be executed on containers (typically to perform database dumps within a Docker Compose setup).

Features

• Execute commands in Docker containers via Docker API
• Standard cron expressions with second precision
• Optional run-on-startup for immediate execution
• Capture and save command output to files
• Structured logging with tracing
• Secure non-root execution

To run the example inside the repository

docker-compose -f docker-compose.example.yml up --build

Quick Start

Docker Compose example

services:
  crooner:
    image: agjini/crooner:0.1.3
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - ./config.toml:/app/config.toml:ro
      - ./backups:/backups
    restart: unless-stopped

Configuration

Create a config.toml file:

[[jobs]]
name = "PostgreSQL Backup"
at = "0 0 2 * * *"  # Every day at 2:00 AM
container = "postgres-container"
command = ["pg_dump", "-U", "postgres", "mydb"]
output_file = "/backups/postgres_backup.sql"
run_on_startup = true

# You can define as many jobs as you want by repeating [[jobs]]

Job Fields

• name: Job identifier (string)
• at: Cron expression (format: second minute hour day month weekday)
• container: Target container name (string)
• command: Command to execute (array of strings)
• output_file: Optional output file path to write the output of the command (string)
• run_on_startup: Execute immediately on startup (boolean, default: false)

Cron Expression Format

┌───────────── second (0-59)
│ ┌─────────── minute (0-59)
│ │ ┌───────── hour (0-23)
│ │ │ ┌─────── day (1-31)
│ │ │ │ ┌───── month (1-12)
│ │ │ │ │ ┌─── weekday (0-6, 0=Sunday)
│ │ │ │ │ │
* * * * * *

Examples:

• 0 0 2 * * * - Every day at 2:00 AM
• 0 */15 * * * * - Every 15 minutes
• 0 0 0 1 * * - First day of every month at midnight

Logging

Control log level with RUST_LOG environment variable:

environment:
  - RUST_LOG=info  # info (default), debug, trace

Use Cases

• Database backups (PostgreSQL, MySQL, MongoDB)
• Cleanup and maintenance tasks
• Data exports and archiving
• Health checks and monitoring

Building

cargo build --release

License

MIT