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Docker & Kubernetes for Developers · Aula

Aplicações com vários contêineres usando Compose

Orquestre vários contêineres Docker, como uma aplicação web e um banco de dados, usando o Docker Compose no desenvolvimento local.

Aplicações com vários contêineres usando Compose é uma aula grátis de Docker & Kubernetes for Developers no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Docker & Kubernetes for Developers, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Docker & Kubernetes for Developers inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

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.

Perguntas Frequentes

A aula “Aplicações com vários contêineres usando Compose” é grátis?

Sim — o texto completo de “Aplicações com vários contêineres usando Compose” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Docker & Kubernetes for Developers, atualize para CoddyKit PRO. O curso de Docker & Kubernetes for Developers inclui 4 aulas no total.

O que vou aprender em “Aplicações com vários contêineres usando Compose”?

Orquestre vários contêineres Docker, como uma aplicação web e um banco de dados, usando o Docker Compose no desenvolvimento local. Você pratica Docker & Kubernetes for Developers com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar Docker & Kubernetes for Developers?

Nenhuma experiência prévia é necessária. Docker & Kubernetes for Developers no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 4.

Quanto tempo leva a aula “Aplicações com vários contêineres usando Compose”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de Docker & Kubernetes for Developers?

Sim. Cada aula de Docker & Kubernetes for Developers inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Criando Dockerfiles para imagens
  2. Construindo imagens Docker personalizadas
  3. Aplicações com vários contêineres usando Compose
  4. Persistindo dados com volumes Docker
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