Create a Rails API + Postgres with Docker from scratch without having to even install Ruby locally

Every time that I have to start a new project (Ruby, Rails, JS…) I always start Docker first! This means, I never install a single Gem or Package on my local machine.

It helps me to avoid conflicts with different versions of the same package, lost dependencies in the system and so on.

Everything that I use for development on my laptop runs in a Docker container, even Neovim.

This is an example of how to create, step by step, a Ruby on Rails API + Postgres and the only thing you need to follow is Docker.

So let's start:

Create the directory for the API

$ mkdir docker-compose-rails-api
$ cd docker-compose-rails-api

Create the Dockerfile

FROM ruby:2.7.3
LABEL Description="Docker Rails API Base"
WORKDIR /app

RUN gem install bundler

CMD exec bin/start.sh

Create the Gemfile

source "https://rubygems.org"

ruby "2.7.3"
gem "rails", "~> 6.1.3.2"

Create the docker-compose.yml

version: "3"
services:
  api:
    restart: on-failure
    build: .
    tty: true
    stdin_open: true
    volumes:
      - .:/app
      - bundle_cache:/usr/local/bundle
    ports:
      - "3000:3000"
    depends_on:
      - db
    environment:
      DATABASE_URL: postgresql://postgres@db/api_development
      TEST_DATABASE_URL: postgresql://postgres@db/api_test
  db:
    image: postgres:latest
    volumes:
      - ./docker/data-volume/postgresql:/var/lib/postgresql/data
    ports:
      - 5456:5432
    environment:
      POSTGRES_HOST_AUTH_METHOD: trust
volumes:
  bundle_cache:

Create a bin/start.sh file

bundle check || bundle install

if [ -f tmp/pids/server.pid ]; then
  rm -f tmp/pids/server.pid
fi

bin/rails s -p 3000 -b 0.0.0.0

And set permissions

$ chmod +x bin/start.sh

Install Rails

$ docker-compose run api gem install rails -v 6.1.3.2

Create the Rails API

$ docker-compose run api rails new . --api --force --database=postgresql --skip-bundle

Replace content of config/database.yml with this:

global: &default
    adapter: postgresql
    pool: 5
    url: <%= ENV["DATABASE_URL"] %>

  development:
    <<: *default

  test:
    <<: *default
    url: <%= ENV["TEST_DATABASE_URL"] %>

  production:
    <<: *default

Start the server

$ docker-compose up -d

Create the database

$ docker-compose run api bin/rails db:create

Voilà!

Go to your browser and check http://0.0.0.0:3000 to see it working!