Docker is a great tool to synchronize dev envinronment on different machine. This resolves the excuse "not work on my machine". This also helps new devs to quickly set up the project without scratching their head with all the missing libs, mismatch versions, etc.

This article will describe how to setup Docker and Docker Compose for a Rails app that uses Postgresql/MySQL as database, Sidekiq and Redis.

Software versions use in this article

Docker version 18.03.1-ce, build 9ee9f40
docker-compose version 1.21.2, build a133471
Ruby 2.6.1
Rails 5
Postgres 10.6
MySQL 5.7.22
Redis 4.0.9

Install Docker and Docker compose

Installation guides for Docker and Docker Compose are well written in Docker docs.

• https://docs.docker.com/install/
• https://docs.docker.com/compose/install/

Dockerfile

FROM ruby:2.6.1
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
RUN mkdir /demoapp
WORKDIR /demoapp
COPY Gemfile /demoapp/Gemfile
COPY Gemfile.lock /demoapp/Gemfile.lock
RUN bundle install
COPY . /demoapp

Docker compose file

version: '3'
services:
  db:
    image: mysql:5.7.22
    volumes:
      - ./tmp/db:/var/lib/mysql
    environment:
      - MYSQL_ROOT_PASSWORD=123456
  redis:
    image: redis:4.0.9
    volumes:
      - ./tmp/redis:/data
  web:
    depends_on:
      - db
      - redis
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/demoapp
    ports:
      - 3000:3000
    environment:
      - REDIS_URL=redis://redis:6379/
  sidekiq:
    depends_on:
      - db
      - redis
    build: .
    command: sidekiq -C config/sidekiq.yml
    volumes:
      - .:/demoapp
    environment:
      - REDIS_URL=redis://redis:6379/

If the app uses PostgreSQL instead of MySQL, the DB image will be like follow:

db:
    image: postgres:10.6
    volumes:
      - ./tmp/db:/var/lib/postgresql/data

If the app uses MongoDB:

version: '3'
services:
  mongodb:
    image: mongo
    ports:
      - "27017:27017"
  web:
    ...
    depends_on:
      - mongodb

Then we'll need to update config/database.yml to point to the DB image:

For MySQL

default: &default
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: root
  password: 123456
  host: db
development:
  <<: *default
  database: demoapp_development

test:
  <<: *default
  database: demoapp_test