1.rb

#routes.rb
Rails.application.routes.draw do
  get 'fresh_updates', to: 'home#fresh_updates', constraints: { format: :xml }
end

#home_controller.rb
class HomeController < ApplicationController
  def fresh_updates
    updater = Updater.new
    updater.call # updates fresh_updates file

    if updater.success?
      respond_to do |format|
        format.xml { render file: 'public/fresh_updates.xml', layout: false }
      end
    else
      render status: :not_found
    end
  end
end