📋 Docker Compose — Summary

You’ve reached the end of the Docker Compose & Multi-Container section. Here’s everything you’ve learned, condensed into a quick reference.

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🐙 What is Docker Compose?

A tool that lets you define and run multiple containers as one application using a single docker-compose.yml file.

One command to start everything:

docker compose up

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🗂️ The docker-compose.yml Structure

services:
  service-name:
    build: ./path-to-dockerfile   # or use 'image:' for pre-built images
    ports:
      - "host:container"
    environment:
      - KEY=value
    depends_on:
      - other-service
    volumes:
      - named-volume:/path/in/container

volumes:
  named-volume:

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🔑 Core Concepts at a Glance

Concept	What it means
Service	One container defined in docker-compose.yml
Network	All services share a network automatically
Service name as hostname	Services reach each other by name (e.g. db, backend)
depends_on	Controls startup order
Named volumes	Persist data across container restarts/removals
build	Build image from a local Dockerfile
image	Pull a pre-built image from Docker Hub

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🚀 Essential Commands

Command	What it does
docker compose up	Start all services
docker compose up --build	Rebuild images then start
docker compose up -d	Start in background (detached mode)
docker compose down	Stop and remove containers
docker compose down -v	Also remove named volumes
docker compose ps	List running services
docker compose logs -f	Follow live logs
docker compose exec <svc> sh	Open a shell in a service container
docker compose build	Rebuild images without starting

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🏗️ Multi-Container App Pattern

A typical full-stack setup:

Frontend (React)  →  Backend (Node.js)  →  Database (PostgreSQL)
     :80                  :4000                   :5432

• Each layer is its own service in docker-compose.yml
• They talk to each other using service names as hostnames
• You access them from your browser via the mapped host ports

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💡 Tips to Remember

• Use restart: on-failure on your backend — the DB might not be ready immediately
• Add .env files and reference them with env_file: to keep secrets out of your YAML
• Use volumes to persist database data — without it, data is lost when the container stops
• docker compose down -v is a full clean reset — use with caution in production!

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🎯 What’s Next?

Now that you know Docker Compose, you’re ready to explore:

• Environment-specific configs — using .env files with Compose
• Docker Compose Watch — hot reload for development
• Production deployments — deploying your Compose stack to a cloud server