9 steps for dockerizing a Rails api-only application

Docker is a program that helps us in containerizing the environment in which development in being done. It helps us in creating a virtualized environment in which we can development applications without interfering with the host machine.

You can download and install Docker by following the official documentation.

In this article, we’ll go through the process of containerizing a Rails api-only application. This article will be part of a series in which we’ll be building the APIs for a job portal application. The code will be available in this repository.

The official documentation does a pretty good job of getting started with creating a Ruby on Rails containerized application. Feel free to reference that source of information as well if you need to.

Step 1: Create a Dockerfile

FROM ruby:2.5.1
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev
RUN mkdir /app
WORKDIR /app
COPY Gemfile /app/Gemfile
COPY Gemfile.lock /app/Gemfile.lock
RUN bundle install
COPY . /app

Step 2: Create a Gemfile

source 'https://rubygems.org'
gem 'rails', '5.2.0'

Step 3: Create an empty Gemfile.lock

Step 4: Create a docker-compose.yml

version: '3'
services:
  linkedin.rails.postgres.db:
    image: postgres
    volumes:
      - ./tmp/db:/var/lib/postgresql/data
  linkedin.rails.web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - linkedin.rails.postgres.db

Step 5: Build the project

docker-compose run linkedin.rails rails new . --api --force --database=postgresql --T

Step 6: Re-build the project due to changes in Gemfile

docker-compose build

Step 7: Replace the contents of config/database.yml with the following:

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

development:
  <<: *default
  database: myapp_development

test:
  <<: *default
  database: myapp_test

Step 8: Create the database

docker-compose run linkedin.rails rake db:create

Step 9: Boot your Rails app

docker-compose up

That’s all. Let me know in the comments if you find any issue while following these steps.