Setup a Ruby on Rails 6 API project with Docker Compose

Published: by Creative Commons Licence

Here is a quick rundown on how to setup a Ruby on Rails 6 API project with Docker Compose.

Prerequisites

Docker and Docker Compose

Docker: https://www.docker.com/get-started

Docker Compose: https://docs.docker.com/compose/install/

For example, I have:

$ docker -v
$ Docker version 19.03.2, build 6a30dfc

$ docker-compose -v
$ docker-compose version 1.24.1, build 4667896b

Ruby

Rails 6 requires Ruby 2.5.0 or newer1.

If the local machine hasn't got Ruby installed, RVM would be a common solution to consider.

For installing RVM with default Ruby and Rails in one command, run:

\curl -sSL https://get.rvm.io | bash -s stable --rails

To verify the successful installation:

$ ruby -v
$ ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin18]

$ rails -v
$ Rails 6.0.2.1

Create a Rails 6 API project

To create a new Ruby on Rails 6 API project, run:

rails new rails-6-api-docker-demo --api --database=postgresql -T -C
  • rails-6-api-docker-demo: The name of the new project.
  • --api: Create an API only project.
  • --database=postgresql: Use PostgresQL as the default database adapter.
  • -T: (Optional) Skip test files. RSpec would be a more common option.
  • -C: (Optional) Skip ActionCable if no WebSockets is needed for the project.

Setup Docker

Create .dockerignore

cd rails-6-api-docker-demo
touch .dockerignore

.dockerignore files essentially works the same way as .gitignore, but for docker containers. You may just use the content from .gitignore file plus the .git folder and .gitignore itself.

gitignore.io can be handy for generating the desired .gitignore file. For example, https://www.gitignore.io/api/git,rails,rubymine gives an example of .gitignore file for git, rails and rubymine IDE.

Here's a complete example: https://gist.github.com/yizeng/eeeb48d6823801061791cc5581f7e1fc

Create Dockerfile

touch Dockerfile

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession.

Full documentation can be found here.

FROM ruby:alpine

RUN apk update && apk add build-base nodejs postgresql-dev tzdata

RUN mkdir /project
WORKDIR /project

COPY Gemfile Gemfile.lock ./
RUN gem install bundler
RUN bundle install

COPY . .

CMD ["bundle", "exec", "rails", "server", "-b", "0.0.0.0"]
  • FROM ruby:alpine: Select the base image to build from. Here uses the latest alpine version of Ruby. Note that the version needs to match the Ruby version in Gemfile. If there is a mismatch (e.g. ruby '2.6.5' in Gemfile), then here would be FROM ruby:2.6.5-alpine. More versions can be found at the Docker Hub.
  • RUN apk update && apk add build-base nodejs postgresql-dev tzdata: Install the required packages inside Docker.
  • RUN mkdir /project: Create a folder called project to host the codebase.
  • WORKDIR /project: Set the working directory to project folder.
  • COPY Gemfile Gemfile.lock ./: Copy the files to the working directory.
  • RUN gem install bundler: Install the bundler gem. It needs to match the version in Gemfile.lock, A specific version can be set like RUN gem install bundler -v 2.0.2.
  • COPY . .: Copy the codebase into Docker.
  • CMD ["bundle", "exec", "rails", "server", "-b", "0.0.0.0"]: Set the start command.

Setup Docker Compose

Create .env

First, create a .env file at the root of the project, so that any environment variables can be put into it and loaded in containers.

touch .env

Create docker-compose.yml

touch docker-compose.yml

Docker compose is a tool to build a multi-container application, where docker-compose.yml is the YAML config file that tells Docker Compose how to build the containers together.

A more detailed documentation can be found here.

version: '3'

services:
  db:
    image: 'postgres:10-alpine'
    volumes:
      - 'postgres:/var/lib/postgresql/data'
    ports:
      - '5432:5432'

  redis:
    image: 'redis:5-alpine'
    command: redis-server
    ports:
      - '6379:6379'
    volumes:
      - 'redis:/data'
    env_file:
      - '.env'

  web:
    depends_on:
      - 'db'
      - 'redis'
    build: .
    ports:
      - '3000:3000'
    volumes:
      - '.:/project'
    env_file:
      - '.env'

volumes:
  redis:
  postgres:

Here defines 3 services in order to run the Rails application:

  • db: The PostgreSQL database service, which uses postgres:10-alpine here for example. It maps port 5432 inside Docker to the same port on local host machine.
  • redis: The Redis caching service, which uses redis:5-alpine here for example. It maps port 6379 inside Docker to the same port on local host machine. This is needed if Sidekiq is used for job processing or Rails caching is set to Redis instead of memcache.
  • web: This is how the Rails API is composed. It depends on db and redis with port 3000 exposed on host machine.

Config database.yml

The default Ruby on Rails' database.yml needs to be configed with the Docker database URL by adding host, username and password to it.

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  host: db
  username: postgres
  password:

development:
  <<: *default
  database: rails_6_api_docker_demo_development

test:
  <<: *default
  database: rails_6_api_docker_demo_test

production:
  <<: *default
  database: rails_6_api_docker_demo_production
  username: rails_6_api_docker_demo
  password: <%= ENV['RAILS_6_API_DOCKER_DEMO_DATABASE_PASSWORD'] %>

Start Rails Server

Build the containers

docker-compose build

Before starting the server, Rails databases need to be created first.

docker-compose run web bundle exec rails db:create
docker-compose run web bundle exec rails db:migrate

Finally, to build and spin up the Rails 6 API server:

docker-compose up --build

Head over to http://localhost:3000 to test it out and start building the real API!

Install RSpec (Optional)

If the project was initialized with -T option that no tests are generated, a testing framework would be needed for the project.

Here is how to add RSpec support.

  1. Add rspec-rails to Gemfile

    # Add it inside group :development, :test
    group :development, :test do
      # some existing gems...
      # ...
    
      gem 'rspec-rails'
    end
    
  2. Rebuild the containers

    docker-compose build
    
  3. Install RSpec

    docker-compose run web bundle exec rails generate rspec:install
    
  4. Run the tests

    docker-compose run web bundle exec rspec
    

Troubleshooting

Error starting userland proxy: listen tcp 0.0.0.0:6379: bind: address already in use

  • Reason: Port 6379 is already in use on local machine.This is most likely that there is another Redis server running locally.

  • Solution: Either stop the Redis on local machine or map to another port in docker-compose.yml, like - '6380:6379'.

Error starting userland proxy: listen tcp 0.0.0.0:5432: bind: address already in use

  • Reason: Port 5432 is already in use on local machine. This is most likely that there is another PostgreSQL server running locally.

  • Solution: Either stop the PostgreSQL on local machine or map to another port in docker-compose.yml, like - '5434:5432'.

Your Ruby version is 2.6.5, but your Gemfile specified 2.6.3
ERROR: Service 'web' failed to build: The command '/bin/sh -c bundle install' returned a non-zero code: 18

  • Reason: There is a Ruby version mismatch between Gemfile and Docker container.

  • Solution: Either update the Ruby version in Gemfile to 2.6.5, or pull explicitly Ruby 2.6.3 image in Dockerfile like FROM ruby:2.6.3-alpine.

/usr/local/bundle/ruby/2.6.0/gems/activesupport-6.0.2.1/lib/active_support/railtie.rb:39:in
rescue in block in <class:Railtie>': tzinfo-data is not present.
Please add gem 'tzinfo-data' to your Gemfile and run bundle install (TZInfo::DataSourceNotFound)
/usr/local/bundle/ruby/2.6.0/gems/tzinfo-1.2.5/lib/tzinfo/zoneinfo_data_source.rb:180:in `initialize':
None of the paths included in TZInfo::ZoneinfoDataSource.search_path are valid zoneinfo directories. (TZInfo::ZoneinfoDirectoryNotFound)

  • Reason: Required tzdata package was not installed in Docker container.

  • Solution: Include tzdata in Dockerfile's RUN apk add command (see details above).

/usr/local/lib/ruby/2.6.0/rubygems.rb:283:in `find_spec_for_exe':
Could not find 'bundler' (2.0.2) required by your /project/Gemfile.lock. (Gem::GemNotFoundException)
ERROR: Service 'web' failed to build: The command '/bin/sh -c bundle install' returned a non-zero code: 1

  • Reason: Required gem bundler was not installed in Docker container.

  • Solution: Include RUN gem install bundler command in Dockerfile (see details above).

  1. https://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html#ruby-versions