Building Multi-Container Apps with Docker

Multi-container applications are essential for modern development. This tutorial demonstrates how to use Docker Compose to define, configure, and deploy applications with multiple services like web apps, databases, and caches.

1. Multi-Container Architecture Overview

Single Service

One container handles one task (e.g., app, DB)

Multi-Service

Connected services working together (e.g., web + DB + cache)

2. Define Services in docker-compose.yml


version: '3.8'
services:
  web:
    image: my-web-app
    ports:
      - "80:80"
    environment:
      DB_HOST: database
  database:
    image: postgres:14
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: example
    volumes:
      - db-data:/var/lib/postgresql/data
volumes:
  db-data:

Key Features in This Configuration

Service linking: Containers can communicate using service names (web → database)
Persistent storage: PostgreSQL data volume for data persistence
Environment configuration: Pass connection parameters to services

3. Start and Manage Containers


# Start all services
docker compose up -d

# View running containers
docker compose ps

# Stop and remove containers
docker compose down

Docker Compose automatically creates a network connecting all services. Containers can reference each other by their service name (e.g., the web app connects to database as the hostname).

4. Scaling Services


# Scale the web service to 3 instances
docker compose up -d --scale web=3

This is particularly useful for load balancing web applications while keeping databases and other stateful services at a single instance.

Advanced Compose Features

Extends

Re-use common service configurations

e.g., shared base configurations

Health Checks

Ensure services are properly running

e.g., healthcheck: curl http://localhost:80

Profiles

Conditional service activation

e.g., run extra services only in dev

When to Use Docker Compose

Use Case	Docker Compose	Kubernetes
Local Development	✓	✗
Production Orchestration	✗	✓
Multi-container Testing	✓	✗
CI/CD Pipeline	✓	✓

Start Building Multi-Container Apps

Use Docker Compose for local development and scale to Kubernetes when ready for production.

Docker Compose Docs Choosing Orchestrators