The Docker Compose file is a YAML file defining services, networks, and volumes. This file is used to spin up multiple containers at once using docker-compose CLI tool. It's designed to be a part of your development process rather than being deployed on its own.

In this guide, we will explore the docker-compose.yml file in detail and provide steps for its installation and usage.

Understanding Docker Compose File

Let's take a look at an example of a docker compose file:

version: '3'
services:
  db:
    image: 'jc21/mariadb-aria:latest'
    container_name: npm-db
    restart: unless-stopped
    env_file: .env
    environment:
      - MYSQL_ROOT_PASSWORD=${MYSQL_ROOT_PASSWORD}
      - MYSQL_DATABASE=${MYSQL_DATABASE}
      - MYSQL_USER=${MYSQL_USER}
      - MYSQL_PASSWORD=${MYSQL_PASSWORD}
      - MARIADB_AUTO_UPGRADE=1
    volumes:
      - ./data/mysql:/var/lib/mysql
    networks:
      - proxy
      - proxydb
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u${MYSQL_USER}", "-p${MYSQL_PASSWORD}"]
      interval: 20s
      timeout: 5s
      retries: 5
      start_period: 30s

  app:
    image: 'jc21/nginx-proxy-manager:latest'
    container_name: nginx-proxy-manager
    restart: unless-stopped
    env_file: .env
    environment:
      - TZ=${TZ}
      - DB_MYSQL_HOST=db
      - DB_MYSQL_PORT=3306
      - DB_MYSQL_USER=${MYSQL_USER}
      - DB_MYSQL_PASSWORD=${MYSQL_PASSWORD}
      - DB_MYSQL_NAME=${MYSQL_DATABASE}
    ports:
      - '80:80'
      - '81:81'
      - '443:443'
    volumes:
      - ./data/npm:/data
      - ./data/letsencrypt:/etc/letsencrypt
    depends_on:
      - db
    networks:
      - proxy
      - proxydb
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:81/api/status"]
      interval: 20s
      timeout: 5s
      retries: 5
      start_period: 40s

networks:
  proxy:
    external: true
  proxydb:
    external: true

This Docker Compose file defines two services, db and app. Each service is defined with its own configuration such as the image to use, ports to expose, volumes to mount, etc. It also has a network section where it lists the networks that these services should connect to.

.env

MYSQL_ROOT_PASSWORD=rhDGjilZm6XEMJ
MYSQL_DATABASE=npm
MYSQL_USER=npm
MYSQL_PASSWORD=rhDGjilZm6XEMJ

# TZ for container timezone
TZ=America/New_York

Installation Guide

Install Docker: Follow instructions on the official Docker website for your specific operating system.
Install Docker Compose: On Linux, run sudo curl -L "https://github.com/docker/compose/releases/download/1.29.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose followed by sudo chmod +x /usr/local/bin/docker-compose. On Windows or MacOS, follow the instructions on Docker Compose's Github page.
Pull Docker Images: Before running docker-compose up, make sure to pull all necessary images with docker-compose pull command.

Running the Services

Running the services: In your terminal, navigate to the directory containing your docker-compose file and run docker-compose up -d. This will start all the services defined in the compose file.
Checking the running status of services: You can check the status of running services with docker-compose ps command.

Remember to replace placeholders like ${MYSQL_ROOT_PASSWORD}, ${MYSQL_DATABASE}, and ${MYSQL_USER}, etc., in your environment variables files (.env) with actual values before starting the services. Also, ensure all paths mentioned in volumes section exist on your system or adjust them accordingly.

Conclusion

With this guide you should now have a solid understanding of Docker Compose file and how to use it for running multi-container applications. It's worth noting that Docker Compose is just one tool among many, each having its own strengths and weaknesses depending on the specific use case.