How to create an inline / minimal Rails app?

Question

It's possible, for example, to use ActiveRecord inline in a Ruby script. I like this a lot to report bugs, test features and share gists.

I'm wondering if the same could be done for a Rails webservice? (I'm mainly interested in getting the controller layer to work, the rest should be easy to add on demand.) Something along these lines:

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  gem 'rails', '~> 6.0.0'
end

require 'rails/commands'
APP_PATH = File.expand_path('config/application', __dir__)
Rails::Command.invoke('server')

When toying around with this it did seem that an external entry point (APP_PATH) is required. So alternatively, an acceptable approach would be to cram all config into the single entry point. I couldn't get this to work so far.

The Rails Initialization Process is the best resource I found about this so far.

I produced a minimal Rails app to get started as follows:

rails new min-rails --skip-keeps --skip-action-mailer --skip-action-mailbox --skip-action-text --skip-active-record --skip-active-storage --skip-puma --skip-action-cable --skip-sprockets --skip-spring --skip-listen --skip-javascript --skip-turbolinks --skip-test --skip-system-test --skip-bootsnap --api
cd min-rails
rm -rf app/jobs app/models config/initializers config/locales lib log public tmp vendor config/environments/test.rb config/environments/production.rb config/credentials.yml.enc config/master.key bin/rake bin/setup bin/bundle

Answer 1

I ended up with the following script:

inline-rails.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  gem 'rails', '~> 6.0.0'
end

require "action_controller/railtie"

class App < Rails::Application
  routes.append do
    get "/hello/world" => "hello#world"
  end

  config.consider_all_requests_local = true # display errors
end

class HelloController < ActionController::API
  def world
    render json: {hello: :world}
  end
end

App.initialize!

Rack::Server.new(app: App, Port: 3000).start

Run it as:

ruby inline-rails.rb