Docker Compose file vs Dockerfile - Differences - Explained

The Dockerfile is used to build a custom image and does not directly generate a container. It’s just that you can run the container while running the image.

The container orchestration to deploy the environment is done using the docker-compose.yml file, which may require a Dockerfile.

Dockerfile is used to build a mirror. If you want to use this mirror, you need to use the docker run command to run the mirror to generate and run a container.

If you have multiple containers and each container is dependent on another container then with docker-compose we can link.

Dockerfile

Write each layer of modification, installation, construction, and operation commands into a script. Use this script to build and customize the image. This script is the Dockerfile.

Dockerfile part of the instructions:

// FROM Specify the base image
FROM nginx

// Excuting an order. Each RUN will generate a layer, and use && as much as possible for a requirement, so as to reduce the RUN, that is, reduce the layering 

RUN echo '<h1>Hello, Docker!</h1>' > /usr/share/nginx/html/index.html
RUN yum update && yum install -y vim python-dev

// COPY: Copy package.json in the source path to the mirror path /usr/src/app on the new layer
COPY package.json /usr/src/app/

// WORKDIR Specify the working directory. Specify the lower-level working directory as /data in the container, try to use an absolute directory
WORKDIR /data

//ADD can automatically decompress files. The following example finally hello under /data/test
ADD hello test/ 

// Copy is similar to ADD, except that files cannot be decompressed
COPY hello test/

// CMD Excuting an order
CMD ["node", "index.js"]

// ENV Set environment variables and define NAME=Happy Feet, then you can use $NAME to execute

ENV VERSION=1.0 DEBUG=on NAME="Happy Feet" // VOLUMES mount


// EXPOSE Port exposure

EXPOSE <Port 1> [<Port 2>...]

Dockerfile example

// 1、创建 Dockerfile
mkdir mynginx
cd mynginx
vim Dockerfile

// 2、输入以下内容并保存：
FROM nginx
RUN echo '<h1>Hello, Docker!</h1>' > /usr/share/nginx/html/index.html

// 在 Dockerfile 目录下执行，生成新的自定义 images
docker build -t nginx:v3 .

Docker-compose

docker-compose is an official open source project, responsible for the rapid orchestration of Docker container clusters and the deployment of distributed applications. Define a group of related application containers as a project through a single docker-compose.yml template file (YAML format)

Install docker-compose

It has been installed by default under Mac and Window. However, it must be installed manually under Linux. The binary package is used here

sudo curl -L https://github.com/docker/compose/releases/download/1.26.0/docker-compose-`uname -s`-`uname -m` > /usr/local/bin/docker-compose
sudo chmod +x /usr/local/bin/docker-compose

// Test docker-compose
$ docker-compose --version

General steps

1. Create an empty directory.

2. Define Dockerfile to facilitate migration to any place

3. Write docker-compose.yml file

4. Run docker-compose up to start the service

Examples of using docker-compose

Next, we use Node JS to build a website that can record the number of page visits.

1. Create an empty directory: mkdir -p /data/test

2. Create index.js under the empty file and enter the following. In createClient() you can apply a hostname that you have mentioned in docker-compose.yml

const express = require('express');
const app = express();
const redis  = require('redis');
app.get('/count',async function (req,res){
    const client = redis.createClient({host: 'redis-server'});
    return client.get('visit',(err, count)=>{
        count=Number(count)+2;
        return client.set(['visit',String(count)],function(err){
        return res.status(200).send(`Total Visit ${count}`);
        })
    });
})
app.get('/ping',(req,res)=>res.send("OK"));
app.listen(3001);

3. Write the Dockerfile file:

FROM node:14
ADD . /code
WORKDIR /code
RUN npm install express redis
COPY . ./code
CMD ["node", "index.js"]

4. Write the docker-compose.yml file

version: '3'
services: 
  redis-server:
    image: 'redis'
  web: 
    build: "."
    ports: 
       - "5001:3001"
    depends_on:
      - redis-server     
    links:
      - redis-server   

5. Execute the docker-compose project

docker-compose up

Description of yml template file:

version: '3'
services:
    phpfpm:
    image: yoogr/phpfpm:0.0.1
    container_name: ct-phpfpm
    build:
      context: .
      dockerfile: Dockerfile
    expose:
      - "9000"
    volumes:
      - ${DIR_WWW}:${DIR_WWW}:rw
      - ./conf/php/php.ini:/usr/local/etc/php/php.ini:ro
      - ./conf/php/php-fpm.d/www.conf:/usr/local/etc/php-fpm.d/www.conf:rw
      - ./conf/supervisor/conf.d:/etc/supervisor/conf.d/:ro
      - ./log/php-fpm/:/var/log/php-fpm/:rw
      - ./log/supervisor/:/var/log/supervisor/:rw
    command: supervisord -n
    links:
      - mysql:mysql
      - redis:redis

Each service represents a container. The container can be created through the image of dockerhub, or it can be created from the image built from the local Dockerfile. If a service needs to use the image built by Dockerfile, specify the text location and file name of the build-in docker-compose. The yml file can specify volume and network. 

The following is an example of using network and volumes parameters (placed in the same layer relationship with service):

version: '3.0'
services:

  wordpress:
    image: wordpress
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_PASSWORD: examplepass
    network:
      - my-bridge

  db:
    image: mysql:5.7
    environment:
      MYSQL_DATABASE: wordpress
      MYSQL_ROOT_PASSWORD: 123456
    volumes:
      - mysql-data:/var/lib/mysql
    networks:
      - my-bridge

volumes:
  my-data

networks:
  my-bridge:
    driver:bridge

The definition of network and volume is similar to docker network create and docker volume create. If you do not specify the connection network, then link will be used. 

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