How to enable rack-mini-profiler in Rails 4

rack-mini-profiler-rails-4.md

1. Add gem in Gemfile:

gem 'rack-mini-profiler', require: false, group: :development

2. Move config.middleware.use Rack::Deflater from config/application.rb to config/environments/production.rb

3. Edit config/initializers/rack_profiler.rb:

if Rails.env.development?
  require 'rack-mini-profiler'
  Rack::MiniProfilerRails.initialize!(Rails.application)
end

4. Edit app/controllers/application_controller.rb:

before_filter :allow_mini_profiler

def allow_mini_profiler
  if Rails.env.development?
    Rack::MiniProfiler.authorize_request
  end
end