How I upgraded a Rails app from version 3 to 4 using continuous delivery, live in production.

1. Continuous Delivery
and Rails Upgrades
@brianauton

2. ● Reliable tests
● Fast deploys
● No big merges

3. Rails Upgrade
● Safe for production?
● Tests always passing?

4. source "https://rubygems.org"
gem "rails", "~> 3.2.22"
gem "jquery-rails"
gem "pdf-reader"
gem "prawn"
# ...

5. source "https://rubygems.org"
if ENV["RAILS4"]
gem "rails", "~> 4.2.4"
else
gem "rails", "~> 3.2.22"
end
gem "jquery-rails"
gem "pdf-reader"
gem "prawn"
# ...

6. > cp Gemfile.lock Gemfile.lock.rails3
> RAILS4=y bundle update rails
> cp Gemfile.lock Gemfile.lock.rails4

7. # config/environment.rb
require File.expand_path('../application', __FILE__)
if ENV["RAILS4"]
Rails.application.initialize!
else
MyApp::Application.initialize!
end

8. > cp Gemfile.lock.rails4 Gemfile.lock
> RAILS4=y bundle
> RAILS4=y rails console
> cp Gemfile.lock.rails3 Gemfile.lock
> bundle
> rails console

9. #!/usr/bin/env/rake
# …
if Rails.env.test? || Rails.env.development?
require "rspec/core/rake_task"
RSpec::Core::RakeTask.new :spec
task :default do
sh "cp Gemfile.lock.rails3 Gemfile.lock"
sh "bundle install --quiet"
sh "rspec"
sh "cp Gemfile.lock.rails4 Gemfile.lock"
sh "RAILS4=y bundle install --quiet"
sh "RAILS4=t rspec"
sh "cp Gemfile.lock.rails3 Gemfile.lock"
sh "bundle install --quiet"
end
end

10. # spec/spec_helper.rb
require 'rspec/rails'
RSpec.configure do |config|
config.include Devise::TestHelpers, type: :config
config.include FactoryGirl::Syntax::Methods
config.around(:each, :rails3_only) do |example|
pending if ENV["RAILS4"]
example.run
end
end
# spec/models/person_spec.rb
it "requires an email address", :rails3_only do
# ...
end

11. source "https://rubygems.org"
if ENV["RAILS4"]
gem "rails", "~> 4.2.4"
else
gem "rails", "~> 3.2.22"
end
gem "jquery-rails"
gem "pdf-reader"
gem "prawn"
# ...

12. Continuous Delivery
● No excuse

13. @brianauton