The site that I used as a reference

In particular, I studied and referred to the top site. The concept is well described, so if you are a reader of this article, please take a look.

-[Series] The most understandable container in the world & Introduction to Docker ~ Part 1: What is a container? ~ -[Difference between RUN instruction and CMD instruction of Dockerfile [Docker]](https://rara-world.com/dockerfile-run-cmd/#:~:text=RUN%E5%91%BD%E4%BB% A4% E3% 83% BBCMD% E5% 91% BD% E4% BB% A4% E3% 81% AE,% E3% 81% A8% E3% 81% 8D% E3% 81% AB% E5% AE% 9F % E8% A1% 8C% E3% 81% 95% E3% 82% 8C% E3% 81% BE% E3% 81% 99% E3% 80% 82) -Docker Document Japaneseization Project -Introduction to Docker (6th) ~ Docker Compose ~ -docker-compose I didn't understand the difference between up, build and start, so I summarized it -I explained how to write docker-compose.yml

Let's do it!

Create a container from Dockerfile

Create a container with PHP and Apache installed on CentOS7.

flow

① Create a Dockerfile in any location (file name: dockerfile) 2 Create an image from the created Dockerfile. ③ Create a container based on the image.

procedure

① First, create a docker file on your PC.

dockerfile

#Based on the centos7 image from Docker Hub.
FROM centos:centos7

#Install Apache and php in centos7 image
RUN yum -y install httpd php

#Execute the command to start Åpach
CMD ["/usr/sbin/httpd","-DFOREGROUND"]

(2) Create an image based on the created Dockerfile.

See Docker Document Japaneseization Project for explanations of options.

#Contents
docker build -t image name:Tag name Dockerfile directory

#Example | The image name is lamptest. Tag is 1.0. Use current directory dockerfile
docker build -t lamptest:1.0 .

The above will create an image.

③ Start the container based on the created image

#Contents
docker run -d -p port number:port number--name Container name Image name:Tag name

#Example | Assign port 80 version to 8080 version.
#The container name is testserver.
#Images and tags are lamptest:1.Use 0.
docker run -d -p 8080:80 --name testserver lamptest:1.0

The container is completed successfully.

When you access [http: // localhost: 8080](http: // localhost: 8080), the following screen will be displayed.

* Supplement * Container operation

#Start-up
docker start container name

#Stop
docker stop container name

#Go inside the container
docker exec -i -t container name bash

The operation is also possible with GUI.

Detailed description of the dockerfile command

The ones that are frequently used are briefly described. Please refer to Docker Document Japaneseization Project for more detailed explanation.

From Create based on Docker image.

#Contents
FROM image name:Tag name

#Example | Based on the image of centos
FROM centos:centos7

Run Execute the command for the image specified in FROM.

#Contents
FROM Command to execute

#Example | Installing httpd with yum
RUN yum -y install httpd

COPY Specify the file you want to copy in the Docker image (in the container).

#Contents
Path of the file you want to copy in the FROM image Path of the copy destination image

#Example | hoge file in the same directory as Dockerfile,/Copy to tmp directory.
COPY hoge.txt /tmp

ADD If you specify a file that can be compressed with a tar archive (gzip, bzip2, xz) that can specify a URL, it will be automatically expanded. Other than that, it is the same as the COPY command.

#Contents
The file path or URL you want to copy into the ADD image The image path of the copy destination.

#Example | tar.Image storage while expanding gz file
ADD hoge.tar.gz /tmp

#Example | Save the URL destination file in the specified directory.
ADD https://zukan.pokemon.co.jp/detail/025 /tmp

RUN Execute the command when creating the image.

#Contents
RUN command option

#Example | ls command-With the option of a.
RUN ls -a

CMD Execute the command when the container starts.

#Contents
CMD [command,option]

#Example | ls command-With the option of a.
CMD [ ls , -a ]

ENV Enter a value in the number of environment variables. (Equal can be omitted.)

#Contents
ENV environment variable name=Environment variable value
ENV environment variable name Environment variable value

#Example | Insert ichinokata into the environment variable MIZUNOKOKYU
ENV MIZUNOKOKYU=ichinokata

USER Switching user execution name

#Contents
USER username

#Example | Switch user name to akiunleash
USER akiunleash

Create and link multiple containers with docker-compose

It is possible to build multiple containers of application and database as one system. Let's create Rails and PostgreSQL containers separately and work together as one system.

flow

① Create necessary files such as docker-compose.yml ② Create images and containers using docker-compose run ③ Gemfile will be updated, so build it again with docker-compose bulde ④ Change the username and password settings so that you can connect to PostgreSQL from the Rails side. ⑤ Create PostgreSQL database from Rails ⑥ Completion!

procedure

Prepare the following four files.

• docker-compose.yml
• dockerfile
• Gemfile
• Gemfile.lock

docker-compose.yml

version: '3'
services:
  db:
    image: postgres
    environment:
      - POSTGRES_PASSWORD=password
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db

dockerfile

#Based on the centos7 image from Docker Hub.
FROM ruby:2.3.3

#From the package management software update
# build-essential libpq-install dev nodejs
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs

#Create myapp directory in the container
RUN mkdir /myapp

#Set in work directory
WORKDIR /myapp

#Create a file in the same directory as dockerfile in the container
ADD Gemfile /myapp/Gemfile
ADD Gemfile.lock /myapp/Gemfile.lock

#Install rails written in Gemfile
RUN bundle install

#Create Rails files and directories in a container
ADD . /myapp

Gemfile

source 'https://rubygems.org'
gem 'rails', '5.0.0.1'

Gemfile.lock

#Empty file

Execute the command in the directory where the above file is saved

docker-compose run web rails new . --force --database=postgresql

The Gemfile will be updated, so execute the command to install the Gem again.

docker-compose build

Edit the information to connect to the database.

config/database.yml

default: &default
  adapter: postgresql
  encoding: unicode
  host: db
  username: postgres
  password: password
  pool: 5

development:
  <<: *default
  database: myapp_development

test:
  <<: *default
  database: myapp_test

production:
  <<: *default
  database: myapp_production
  username: myapp
  password: <%= ENV['MYAPP_DATABASE_PASSWORD'] %>

Let's start the app!

docker-compose up -d

Since there is no database in the current state, we will create it.

docker-compose run web rake db:create

Confirmation!

If you access [http: // localhost: 3000 /](http: // localhost: 3000 /) and the following page is displayed, it is successful.

You can see that the container is also started properly.

If it contains unnecessary containers, it will go down once and disappear when you restart.

#Once down
docker-compose down

#Side up
docker-compose up -d

Explanation of docker-compose.yml

docker-compose.yml

version: '3'
services:
  db:
    image: postgres
    environment:
      - POSTGRES_PASSWORD=password
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db

Finally

I hope it helps you get a feel for what Docker is all about. If you find any mistakes in the content, please let us know.

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