Sample Docker Compose Configuration File

Docker containers can be started using command-line arguments, but as applications become more complex, managing them manually becomes difficult. Docker Compose solves this problem by allowing you to define containers, networks, volumes, and environment variables in a single YAML configuration file.

A Docker Compose file makes application deployment easier, more consistent, and easier to maintain.

Example Docker Compose File

services:
  app:
    container_name: my_container

    image: ubuntu:latest

    ports:
      - "8080:80"
      - "443:443"

    environment:
      MYSQL_ROOT_PASSWORD: my_password
      MYSQL_DATABASE: my_database
      MYSQL_USER: my_user
      MYSQL_PASSWORD: my_database_password

    volumes:
      - ./data:/app/data

    command: ["npm", "start"]

    restart: always

Understanding the Configuration

container_name

The container name defines how the container will appear in Docker.

container_name: my_container

Without this option, Docker automatically generates a random name.

image

The image specifies which Docker image should be used when creating the container.

image: ubuntu:latest

Docker will automatically download the image if it is not already available on the server.

ports

Port mappings allow external traffic to reach services running inside the container.

ports:
  - "8080:80"
  - "443:443"

In this example:

• Port 8080 on the server forwards traffic to port 80 inside the container.
• Port 443 on the server forwards traffic to port 443 inside the container.

environment

Environment variables provide configuration values to applications running inside the container.

environment:
  MYSQL_ROOT_PASSWORD: my_password
  MYSQL_DATABASE: my_database
  MYSQL_USER: my_user
  MYSQL_PASSWORD: my_database_password

These values are commonly used by databases, web applications, and other services.

volumes

Volumes allow data to persist even if the container is removed and recreated.

volumes:
  - ./data:/app/data

In this example:

• ./data is a directory on the host server.
• /app/data is the directory inside the container.

Any changes made in either location are synchronized.

command

The command option overrides the image’s default startup command.

command: ["npm", "start"]

When the container starts, Docker executes this command.

restart

The restart policy controls what happens if a container stops unexpectedly.

restart: always

Common options include:

Policy	Description
no	Never restart automatically
always	Always restart the container
unless-stopped	Restart unless manually stopped
on-failure	Restart only after failures

Starting the Application

Save the configuration as:

docker-compose.yml

Then start the container:

docker compose up -d

The -d flag runs the container in the background.

Viewing Running Containers

To display running containers:

docker ps

To view application logs:

docker compose logs

To stop the application:

docker compose down

Example: WordPress with MariaDB

Docker Compose is often used to deploy multiple services together.

services:
  db:
    image: mariadb:latest
    environment:
      MYSQL_ROOT_PASSWORD: strongpassword
      MYSQL_DATABASE: wordpress

  wordpress:
    image: wordpress:latest
    ports:
      - "8080:80"
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_NAME: wordpress
      WORDPRESS_DB_PASSWORD: strongpassword

This configuration launches both a WordPress container and a MariaDB database container that automatically communicate with each other.

Summary

Docker Compose allows you to define container configurations in a simple YAML file instead of managing long Docker commands manually. It simplifies application deployment by centralizing configuration such as images, ports, environment variables, storage volumes, and restart policies.

For modern applications that use multiple containers, Docker Compose is one of the most commonly used tools for local development, testing, and small-to-medium production environments.