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Docker & Kubernetes for Developers · Lezione

Applicazioni multi-container con Compose

Orchestri più container Docker, come un'app web e un database, utilizzando Docker Compose per lo sviluppo locale.

Applicazioni multi-container con Compose è una lezione Docker & Kubernetes for Developers gratuita su CoddyKit. Questa è la lezione 3 di 4. Puoi leggere la lezione completa qui gratuitamente — poi esercitati direttamente nel browser con un editor di codice integrato e un tutor IA disponibile 24/7. Fa parte del percorso di apprendimento Docker & Kubernetes for Developers, e i tuoi progressi si sincronizzano tra il web e l'app CoddyKit. Il corso Docker & Kubernetes for Developers include 4 lezioni in totale.

Parti di questa lezione non sono ancora state tradotte e vengono mostrate in inglese.

Why Multi-Container Apps?

In real-world applications, you rarely have just one component. Imagine a web application: you need a web server (like Nginx), a backend application (like Python Flask), and a database (like Redis or PostgreSQL).

Each of these components has its own dependencies and configuration. Managing them individually and ensuring they communicate correctly can quickly become complex.

Meet Docker Compose

Docker Compose is a tool designed to simplify the process of defining and running multi-container Docker applications.

  • You define your entire application's services (containers) in a single YAML file.
  • Then, with one simple command, Compose creates and starts all the services for you.
  • It's incredibly useful for local development and testing environments.

The Compose YAML File

The heart of Docker Compose is the docker-compose.yml file. This YAML file describes your application's services, networks, and volumes.

It typically starts with a version key, followed by the main services section where you define each container that makes up your application.

Defining Services

Under the services section, you list each component of your application. Each service corresponds to a Docker container.

Key properties for defining a service include:

  • image: Specifies the Docker image to use (e.g., nginx:latest).
  • build: Provides the path to a directory containing a Dockerfile to build a custom image.
  • container_name: An optional, fixed name for your container, making it easier to reference.

Exposing & Configuring Services

You often need to expose your services to the host machine or configure them with environment variables.

  • ports: Maps ports from the host to the container (e.g., "8080:80" maps host port 8080 to container port 80).
  • environment: Passes environment variables into the container (e.g., DB_HOST: "database").

These settings are crucial for communication and customization.

Connecting Your Services

When you use Docker Compose, it automatically creates a default network for your application. All services defined in your docker-compose.yml file join this network.

This allows services to communicate with each other using their service names as hostnames. For example, a web app service can connect to a database service named redis by simply using redis as the hostname.

Example: Python + Redis

Let's build a simple multi-container application: a Python Flask web app that counts how many times it has been visited, storing the count in a Redis database.

This setup clearly shows how a 'web' service can interact with a 'database' service within a single Compose application.

Web App Code & Dockerfile

Here's our simple Python Flask application (app.py) and its Dockerfile. The Flask app connects to the redis service, and the Dockerfile packages it all up.

# app.py
import time
import redis
from flask import Flask

app = Flask(__name__)
# Connects to 'redis' service in Compose network
cache = redis.Redis(host='redis', port=6379)

def get_hit_count():
    retries = 5
    while True:
        try:
            return cache.incr('hits')
        except redis.exceptions.ConnectionError as exc:
            if retries == 0:
                raise exc
            retries -= 1
            time.sleep(0.5)

@app.route('/')
def hello():
    count = get_hit_count()
    return 'Hello from CoddyKit! I have been seen {} times.\n'.format(count)

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000, debug=True)

# requirements.txt
# flask
# redis

# Dockerfile
FROM python:3.9-slim-buster
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 5000
CMD ["python", "app.py"]

Your First Compose File

This docker-compose.yml ties everything together. It defines two services: web (our Python app, built from the current directory) and redis (using the official Redis image).

Try running this example!

version: '3.8'
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"

Managing Your Compose App

To start your multi-container application in detached mode (in the background), navigate to the directory containing your docker-compose.yml and supporting files, then run:

docker compose up -d

To see the running services and their status:

docker compose ps

To stop and remove the containers, networks, and volumes created by Compose:

docker compose down

Compose Configuration Check

Consider the following docker-compose.yml snippet:

version: '3.8'
services:
  app:
    build: .
    ports:
      - "8080:80"
  database:
    image: "postgres:13"

Which statement is TRUE about this configuration?

Recap: Docker Compose

You've learned how Docker Compose simplifies managing multi-container applications for local development!

  • It uses a docker-compose.yml file to define all your services.
  • Services can communicate with each other using their service names on a default network.
  • Commands like docker compose up and docker compose down manage your entire application stack with ease.

Docker Compose is an essential tool for local development setups involving multiple Docker containers.

Domande Frequenti

La lezione «Applicazioni multi-container con Compose» è gratuita?

Sì — il testo completo di «Applicazioni multi-container con Compose» è gratuito qui sul web. Per esercitarvi in modo interattivo (un editor di codice integrato e un tutor IA 24/7) e sbloccare il resto del corso Docker & Kubernetes for Developers, passa a CoddyKit PRO. Il corso Docker & Kubernetes for Developers include 4 lezioni in totale.

Cosa imparerò in «Applicazioni multi-container con Compose»?

Orchestri più container Docker, come un'app web e un database, utilizzando Docker Compose per lo sviluppo locale. Eserciti Docker & Kubernetes for Developers con codice pratico che esegui direttamente nel browser, e un tutor IA 24/7 risponde alle tue domande mentre lavori sulla lezione.

Ho bisogno di esperienza per iniziare Docker & Kubernetes for Developers?

Non è richiesta alcuna esperienza precedente. Docker & Kubernetes for Developers su CoddyKit è strutturato per principianti e studenti avanzati, quindi puoi iniziare da qui o dall'inizio e procedere al tuo ritmo. Questa è la lezione 3 di 4.

Quanto tempo richiede la lezione «Applicazioni multi-container con Compose»?

La maggior parte delle lezioni CoddyKit richiede circa 5–10 minuti. Ogni lezione è breve e interattiva, quindi fai progressi costanti e riprendi esattamente da dove hai lasciato su web e app.

Posso scrivere ed eseguire codice in questa lezione Docker & Kubernetes for Developers?

Sì. Ogni lezione Docker & Kubernetes for Developers include un editor di codice integrato, quindi scrivi ed esegui codice reale direttamente nel tuo browser e ricevi feedback istantaneo dall'IA — nessuna configurazione locale necessaria.

Tutte le lezioni di questo corso

  1. Creazione di Dockerfile per le immagini
  2. Creazione di immagini Docker personalizzate
  3. Applicazioni multi-container con Compose
  4. Conservare i dati con i volumi Docker
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