Step 1:

First, using Dockfile to Define the project

we need to create Dockefile, you can cop sample dockerfile from offical websie (This is sample Dockerfile copy from docker offical website)

FROM ruby:2.5
RUN apt-get update -qq && apt-get install -y nodejs postgresql-client
RUN mkdir /myapp
WORKDIR /myapp
COPY Gemfile /myapp/Gemfile
COPY Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
COPY . /myapp

# Add a script to be executed every time the container starts.
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]
EXPOSE 3000

# Start the main process.
CMD ["rails", "server", "-b", "0.0.0.0"]

second, create a Gemfile to just load rails.

source 'https://rubygems.org'
gem 'rails', '~>5' # specify rails version in here

Third, create an empty Gemfile.lock To build Dockefile

touch Gemfile.lock

Fourth, create shell script, named entrypoint.sh

The purpose of entrypoint scipt is to fix a Rails-specific issue that prevents the server from restarting when a certain server.pid file pre-exists.

#!/bin/bash
set -e

# Remove a potentially pre-existing server.pid for Rails.
rm -f /myapp/tmp/pids/server.pid

# Then exec the container's main process (what's set as CMD in the Dockerfile).
exec "$@"

Finaly,create docker-compose.yml file

version: '3'
services:
  db:
    image: mysql
    volumes:
      - ./tmp/db:/var/lib/mysql/data
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db

Step 2: Build the project

Now it’s time to generate the rails skelton app using docker compose run command:

docker-compose run web rails new . --force --no-deps --database=postgresql

If you ever modify gem file. which you’ll do. you need run:

docker-compose build

Step 3: Connect the database

This is tricky part. when I followed docker website. I was stuck in this step. the offical mysql docker image which is somehow can’t initial. I got

[ERROR] --initialize specified but the data directory has files in it. Aborting.

After google for a while. I found a solution which is change db image source in docker-compose.yml file

from image: mysql to image: mariadb the detail discuss about this issue is here

Now we can boot the app with docker-compose up:

docker-compose up Finally, you need to create the database. In another terminal, run: docker-compose run web rake db:create