Ensuring proper order of rack middlewares

error_displayer.rb

  MyApp::Application.config.middleware.insert_before ActionDispatch::ShowExceptions, ExceptionNotifier,
  :sender_address => "sender@gmail.com",
  :exception_recipients => "receiever@gmail.com",
MyApp::Application.config.middleware.insert_after ExceptionNotifier, ActionDispatch::ShowExceptions

require 'action_dispatch/middleware/show_exceptions'
module ActionDispatch
  class ShowExceptions
    private
    def render_exception_with_template(env, exception)
      env[:exception] = exception
      body = ErrorsController.action(rescue_responses[exception.class.name]).call(env)
      log_error(exception)
      MailNotifications.fix_asap(clean_backtrace(exception, :all)).deliver if Rails.env.production? # hope this does not throw any exceptions
      body
    rescue
      render_exception_without_template(env, exception)
    end

    alias_method_chain :render_exception, :template
  end
end