Docker Wait for Dependencies

A lightweight Docker container that ensures service dependencies are available before proceeding. This tool is perfect for orchestrating service startup order in Docker Compose environments.

Features

• 🔍 TCP port availability checking
• ⚡ Lightweight Alpine-based image
• 🔒 Runs as non-root user for security
• 🏗️ Multi-architecture support (amd64, arm64)
• ⏱️ Configurable timeout and check intervals
• 🚀 Zero dependencies beyond netcat

Quick Start

1. Pull the image:

docker pull ducktors/docker-wait-for-dependencies

2. Use in your docker-compose.yml:

version: '3.8'
services:
  mongo:
    image: mongo:6
    ports:
      - 27017:27017
    networks:
      - app-network

  redis:
    image: redis:6
    ports:
      - 6379:6379
    networks:
      - app-network

  wait-for-deps:
    image: ducktors/docker-wait-for-dependencies
    depends_on:
      - mongo
      - redis
    command: mongo:27017 redis:6379
    networks:
      - app-network

  app:
    image: your-app
    depends_on:
      wait-for-deps:
        condition: service_completed_successfully
    networks:
      - app-network

networks:
  app-network:
    driver: bridge

Configuration

Environment Variables

Variable	Default	Description
SLEEP_LENGTH	2	Time in seconds between dependency checks
TIMEOUT_LENGTH	300	Maximum time in seconds to wait for dependencies

Example with Custom Configuration

wait-for-deps:
  image: ducktors/docker-wait-for-dependencies
  environment:
    - SLEEP_LENGTH=1
    - TIMEOUT_LENGTH=60
  command: mongo:27017 redis:6379

Usage Examples

Basic Usage

docker run --rm ducktors/docker-wait-for-dependencies localhost:5432

Multiple Dependencies

docker run --rm ducktors/docker-wait-for-dependencies \
  postgres:5432 \
  redis:6379 \
  elasticsearch:9200

With Custom Timeout

docker run --rm \
  -e TIMEOUT_LENGTH=120 \
  ducktors/docker-wait-for-dependencies \
  mysql:3306

How It Works

1. The container checks each specified host:port combination
2. It waits until all services are available or timeout is reached
3. Returns exit code 0 if all services are available
4. Returns exit code 1 if timeout is reached or invalid input

Contributing

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

License

This project is licensed under the MIT License - see the LICENSE file for details.