# Docker Compose File Guide

## Overview
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:
```yaml
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
```yaml
MYSQL_ROOT_PASSWORD=rhDGjilZm6XEMJ
MYSQL_DATABASE=npm
MYSQL_USER=npm
MYSQL_PASSWORD=rhDGjilZm6XEMJ

# TZ for container timezone
TZ=America/New_York
```
## Installation Guide
1. **Install Docker**: Follow instructions on the official [Docker website](https://docs.docker.com/get-docker/) for your specific operating system.
   
2. **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](https://github.com/docker/compose).
   
3. **Pull Docker Images**: Before running docker-compose up, make sure to pull all necessary images with `docker-compose pull` command. 

## Running the Services
4. **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.
   
5. **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.
