How to create a Rails application using Docker

To follow this tutorial, the only thing you need is to have Docker installed in your computer. Previous knowledge about Docker or Rails isn't necessary. This a newbie to newbie documentation so you can use it "by the book" to start your studies or if you want to run a rails application using docker for the first time.

Creating your app structure

Step 1

Run this code line in your computer bash. It will run a new container with Ruby image

docker run -it -v $HOME:/var/home -w /var/home ruby:3.0.2 bash

Step 2

Installing Ruby package manager (bundler). Run this code line in your computer bash.

gem install bundler

Step 3

Installing Rails. Run this code line in your computer bash.

gem install rails

Step 4

Creating your app. Run this code line in your computer bash. The command --database=postgresql is only necessary if you want to work with postgre. By default, your application will be created using SQLite.

rails new dummy --database=postgresql

Step 5

Installing node. Run this code line in your computer bash.

curl -sL https://deb.nodesource.com/setup_14.x | bash - && \
    echo 'deb https://dl.yarnpkg.com/debian/ stable main' > /etc/apt/sources.list.d/yarn.list &&\
    wget -q -O - https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - &&\
    apt-get update -qq && \
    apt-get install -y build-essential nodejs yarn

Creating a Ruby container to start your application, to use it's bash, console etc.

Step 1

Creating a Dockerfile (it will contain the instructions to create your app image inside a container). Go inside your application and, at the global directory, create a document with the name 'Dockerfile'.

FROM ruby:3.0.2

RUN gem install bundler

RUN curl -sL https://deb.nodesource.com/setup_14.x | bash - && \
    echo 'deb https://dl.yarnpkg.com/debian/ stable main' > /etc/apt/sources.list.d/yarn.list &&\
    wget -q -O - https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - &&\
    apt-get update -qq && \
    apt-get install -y build-essential nodejs yarn

WORKDIR /var/app

COPY . .

RUN bundler install

ENTRYPOINT ["./entrypoint.sh"]

Step 2

Creating an entrypoint (it will contain some commands that your application will run by default, if you dont specify any other command). Create the 'entrypoint.sh' inside your app's global directory.

#!/bin/bash
rm -f /var/app/tmp/pids/server.pid
bundle check > /dev/null 2>&1 || bundle install -j4
echo "> Executing 'yarn install' on web"
yarn install

if [ "$#" == 0 ]
then
    bundle exec rake db:create db:migrate
    exec bundle exec rails server -b '0.0.0.0'
fi
exec $@

Step 3

Adding permission to your app execute it's entrypoint. Insert this command line in your bash, inside your app's directory.

chmod +x entrypoint.sh

Step 4

Building your application. In other words, executing your Dockerfile. Insert this command line in your bash, inside your app's directory.

docker build -t myapp .

Step 5

Starting your container. Insert this command line in your bash, inside your app's directory.

docker run -it myapp bash

Step 6

Executing your container (remember, you started it before in the previous step). Insert this command line in your bash, inside your app's directory.

Get your container id, using this command line

docker ps

then execute it

docker exec -it "id do container" bash

Creating a docker compose

Docker compose is a way to compose your application with diferent containers("services").

Step 1

Inside your application's global directory, create a document with the name 'docker-compose.yml' with the following code block. If you didn't specify the postgre database, paste it without the 'db' code block.

version: '2'

services:
  web:
    build:
      context: .
    volumes:
      - .:/var/app
    ports:
      - '3000:3000'
  db:
      image: postgres:9.6.2-alpine
      ports:
          - '5432:5432'
      volumes:
          - postgres96:/var/lib/postgresql/data
volumes:
  postgres96:

Step 2 (only if you don't have docker-compose installed in your computer)

Insert this command line in your bash, inside your app's directory.

sudo apt install docker-compose

Step 3

Building the docker-compose you have just created. Insert this command line in your bash, inside your app's directory.

docker-compose up

Step 4

If you get a webpack error, this will solve it. Insert this command line in your bash, inside your app's directory.

Open your container bash

docker-compose run web bash

then install the webpacker

bundle exec rake webpacker:install

Step 5

If you get a postgre error, this will solve it

• Search the document config/database.yml
• Inside it, search for the following code block:

development:
...
"database: database name"

then change the "database" line to:

url: postgres://postgres:@db:5432/dummy_development

Now search for the following code block:

test:
...
"database: database name"

then change the "database" line to:

test:
...
url: postgres://postgres:@db:5432/dummy_test

After finishing these changes, execute the command

docker-compose run web bash

Creating a Makefile

A Makefile is a way to create shortcuts as commands to handle your application's usability.

Step 1

Go inside your application and, at the global directory, create a document with the name 'Makefile'. Inside it, insert the following code block:

start:
	docker-compose up
bash:
	docker-compose exec web bash
console:
	docker-compose exec web bundle exec rails c
# specs:
# 	docker-compose exec web bundle exec rspec spec

Step 2

Now, if you want to start your application, access it's bash or console, you can use:

make start
make bash
make console

License

MIT