Recently I was asked to separate the public from the administration portion of a web application and deploy them to different servers. I'll present a Rails application where the admin and public portions are activated based on an application running mode flag. In order to achieve this the application components are separated in Rails engines, and I'll go trough some common pitfalls with this approach as well as discussing its long term benefits.

1. feature flagging
with Ruby on Rails engines
Enrico Teotti -- @agenteo

2. admin user interface
public user interface
domain logic

3. requirement
run the private and public portions of the app
on separate servers

4. service oriented architecture
first proposal

5. two apps sharing components via engines
second proposal

6. local rails engines components
third proposal

7. public_uiadmin_ui

8. Rails.application.routes.draw do
case AppRunningMode .value
when :admin
mount AdminUi::Engine => "/"
when :public
mount PublicUi::Engine => "/"
else
mount AdminUi::Engine => "/"
mount PublicUi::Engine => "/"
end
end
config/routes.rb

9. RUNNING_MODE=public rails
s
RUNNING_MODE=admin rails s
http://worldwideshipping-super-secret-domain.com/admin
http://worldwideshipping.com
rails s
http://localhost:3000

10. ● are ruby gems
● are special ruby gems that provide extra
behaviour (models, views, routes, rake
tasks) to a Rails application
● they can be hosted on a gemserver or
they can live inside your repository
● can be tested in isolation
rails engines

11. admin user interface
public user interface
domain logic

12. mkdir components

13. rails plugin new admin_ui --mountable --dummy=spec/dummy -O -T
mv admin_ui components

14. admin user interface
public user interface
domain logic
admin_ui

15. proceeding without automated tests
could drive you crazy

16. shared user interface (preview)
shared domain
admin_ui

17. Rails.application.routes.draw do
# ... public routes here
mount AdminUi::Engine => "/"
end
config/routes.rb

18. gem 'admin_ui', path: 'components/admin_ui'
Gemfile

19. public user interface
admin_ui
public_ui

20. rails plugin new public_ui --mountable --dummy=spec/dummy -O -T

21. gem 'admin_ui', path: 'components/admin_ui'
gem 'public_ui', path: 'components/public_ui'
Gemfile

22. public_uiadmin_ui

23. Gem::Specification.new do |s|
# ... other fields up here
s.name = "public_ui"
s.add_dependency "rails", "~> 4.1.1"
s.add_dependency 'jquery-rails'
s.add_dependency 'mongoid'
s.add_runtime_dependency "admin_ui"
s.add_development_dependency'byebug'
s.add_development_dependency'database_cleaner'
s.add_development_dependency'rspec-rails', '2.99.0'
s.add_development_dependency'capybara'
s.add_development_dependency'poltergeist'
end
public_ui.gemspec

24. Gem::Specification.new do |s|
# ... other fields up here
s.name = "public_ui"
s.add_dependency "rails", "~> 4.1.1"
s.add_dependency 'jquery-rails'
s.add_dependency 'mongoid'
s.add_runtime_dependency "admin_ui"
s.add_development_dependency 'byebug'
s.add_development_dependency 'database_cleaner'
s.add_development_dependency 'rspec-rails', '2.99.0'
s.add_development_dependency 'capybara'
s.add_development_dependency 'poltergeist'
end
public_ui.gemspec

25. Rails.application.routes.draw do
case AppRunningMode .value
when :admin
mount AdminUi::Engine => "/"
when :public
mount PublicUi::Engine => "/"
else
mount AdminUi::Engine => "/"
mount PublicUi::Engine => "/"
end
end
config/routes.rb

26. the two engines are now glued together!

27. admin_ui public_ui
domain_logic

28. rails plugin new domain_logic --dummy-path=spec/dummy --mountable
-O -T

29. admin_ui public_ui
shared_ui domain_logic

30. rails plugin new shared_ui --dummy-path=spec/dummy --mountable -O
-T

31. <%= render partial: 'shared_ui/cargos/show' %>
admin_ui/app/views/cargo_preview/show.html.erb
<%# admin console stuff here %>
<%= render partial: 'shared_ui/cargos/show' %>
<%# admin spaceship here %>
public_ui/app/views/cargos/show.html.erb

32. gem 'domain_logic' , path: 'components/domain_logic'
gem 'shared_ui', path: 'components/shared_ui'
gem 'admin_ui', path: 'components/admin_ui'
gem 'public_ui', path: 'components/public_ui'
Gemfile

33. #gem 'domain_logic', path: 'components/domain_logic'
#gem 'shared_ui', path: 'components/shared_ui'
gem 'admin_ui', path: 'components/admin_ui'
gem 'public_ui', path: 'components/public_ui'
Gemfile

34. $ bundle
Resolving dependencies...
Could not find gem 'shared_ui (>= 0) ruby', which is required by
gem 'admin_ui (>= 0) ruby', in any of the sources.

35. common pitfalls in Rails engines land

36. Gem::Specification.new do |s|
# ... other fields up here
s.name = "admin_ui"
s.add_dependency "rails", "~> 4.1.1"
s.add_dependency 'jquery-rails'
s.add_dependency 'mongoid'
s.add_dependency 'faraday'
s.add_dependency "domain_logic"
s.add_dependency "shared_ui"
s.add_development_dependency'byebug'
s.add_development_dependency'database_cleaner'
s.add_development_dependency'rspec-rails', '2.99.0'
s.add_development_dependency'vcr'
s.add_development_dependency'webmock'
s.add_development_dependency'capybara'
s.add_development_dependency'poltergeist'
end
admin_ui.gemspec

37. Gem::Specification.new do |s|
# ... other fields up here
s.name = "admin_ui"
s.add_dependency "rails", "~> 4.1.1"
s.add_dependency 'jquery-rails'
s.add_dependency 'mongoid'
s.add_dependency 'faraday'
s.add_dependency "domain_logic"
s.add_dependency "shared_ui"
s.add_development_dependency 'byebug'
s.add_development_dependency 'database_cleaner'
s.add_development_dependency 'rspec-rails', '2.99.0'
s.add_development_dependency 'vcr'
s.add_development_dependency 'webmock'
s.add_development_dependency 'capybara'
s.add_development_dependency 'poltergeist'
end
admin_ui/admin_ui.gemspec

38. source "https://rubygems.org"
gem 'domain_logic', path: '../domain_logic'
gem 'shared_ui', path: '../shared_ui'
# Declare your gem's dependencies in admin_ui.gemspec.
# Bundler will treat runtime dependencies like base
dependencies, and
# development dependencies will be added by default to
the :development group.
gemspec
admin_ui/Gemfile

39. require

40. the test dummy app

41. require File.expand_path("../dummy/config/environment", __FILE__)
admin_ui/spec/rails_helper.rb
admin_ui/spec/dummy/config/boot.rb
# Set up gems listed in the Gemfile.
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../../../Gemfile', __FILE__)
require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
$LOAD_PATH.unshift File.expand_path('../../../../lib', __FILE__)
Rails.application.routes.draw do
mount AdminUi::Engine => "/admin_ui"
end
admin_ui/spec /dummy/config/routes.rb

42. Rails.application.routes.draw do
mount AdminUi::Engine => "/admin_ui"
end
admin_ui/spec /dummy/config/routes.rb

43. testing multiple engines

44. #!/bin/bash
unset BUNDLE_GEMFILE
result=0
if [ "$CI" == "true" ]; then
BUNDLE_PATH="$HOME/vendor/bundle"
fi
for test_script in $(find . -name test.sh); do
pushd `dirname $test_script` > /dev/null
./test.sh
result+=$?
popd > /dev/null
done
if [ $result -eq 0 ]; then
echo "SUCCESS"
else
echo "FAILURE"
fi
exit $result
https://github.com/shageman/the_next_big_thing/blob/master/build.sh

45. require_dependency "admin_ui/application_controller"
module AdminUi
class CargosController < ApplicationController

46. module AdminUi
class CargosController < AdminUi::ApplicationController

47. module AdminUi
class VoyagesController < ApplicationController

48. module AdminUi
class VoyagesController < ApplicationController

49. scaffolding and other generators

50. rails generate scaffold_controller admin_ui/cargo source
destination weight --model-name=DomainLogic::Cargo --orm=mongoid
-t=''

51. require_dependency "admin_ui/domain_logic/application_controller"

52. Failures:
1) Staff booking a cargo booking a cargo fitting a pending voyage
Failure/Error: visit '/admin/cargos'
LoadError:
No such file to load -- admin_ui/domain_logic/application_controller
# ./engines/admin_ui/app/controllers/admin_ui/cargos_controller.rb:1:in `<top (required)>'
# ./spec/features/book_cargo_spec.rb:12:in `block (2 levels) in <top (required)>'
Finished in 0.03067 seconds (files took 1.85 seconds to load)
2 examples, 1 failure

53. Failures:
1) Staff booking a cargo booking a cargo fitting a pending voyage
Failure/Error: visit '/admin/cargos'
RuntimeError:
Circular dependency detectedwhile autoloading constant AdminUi::AdminUi::CargosHelper
# ./engines/admin_ui/app/controllers/admin_ui/application_controller.rb:2:in `<module:AdminUi>'
# ./engines/admin_ui/app/controllers/admin_ui/application_controller.rb:1:in `<top (required)>'
# ./engines/admin_ui/app/controllers/admin_ui/cargos_controller.rb:1:in `<top (required)>'
# ./spec/features/book_cargo_spec.rb:12:in `block (2 levels) in <top (required)>'

54. Failures:
1) Staff booking a cargo booking a cargo fitting a pending voyage
Failure/Error: visit '/admin/cargos'
ActionView::Template::Error:
undefined local variable or method `new_domain_logic_cargo_path' for #<#<Class:0x007fb38887bb38>:
0x007fb388873690>
# ./engines/admin_ui/app/views/admin_ui/cargos/index.html.erb:29:in
`_engines_admin_ui_app_views_admin_ui_cargos_index_html_erb__4343322268368929370_70204533119300'
# ./spec/features/book_cargo_spec.rb:12:in `block (2 levels) in <top (required)>'

55. fang:domain_logic agenteo$ rails generate mongoid:config
/Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/mongoid-4.0.0/lib/rails/generators /mongoid/config/config_generator.rb: 16:in
`app_name': undefined method `parent' for nil:NilClass (NoMethodError)
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/command.rb: 27:in `run'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/invocation.rb: 126:in `invoke_command'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/invocation.rb: 133:in `block in invoke_all'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/invocation.rb: 133:in `each'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/invocation.rb: 133:in `map'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/invocation.rb: 133:in `invoke_all'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/group.rb: 232:in `dispatch'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/thor-0.19.1/lib/thor/base.rb: 440:in `start'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/railties -4.1.4/lib/rails/generators.rb: 157:in `invoke'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/railties -4.1.4/lib/rails/commands /generate.rb: 11:in `<top (required)
>'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/railties -4.1.4/lib/rails/engine/commands.rb: 19:in `require'
from /Users/agenteo/.rvm/gems/ruby-2.1.2@worldwide_shipping /gems/railties -4.1.4/lib/rails/engine/commands.rb: 19:in `<top (required) >'
from bin/rails:12:in `require'
from bin/rails:12:in `<main>'

57. FOLLOWUP READS
http://guides.rubyonrails.org/engines.html
http://pivotallabs.com/tag/cobra/
https://leanpub.com/cobra
http://teotti.com
Enrico Teotti @agenteo enrico@teotti.com