How can I show 404 error page instead of routing error?

in ApplicationController

 rescue_from ActiveRecord::RecordNotFound, :with => :rescue404
 rescue_from ActionController::RoutingError, :with => :rescue404

  def rescue404
    #your custom method for errors, you can render anything you want there
  end

This return 404 page

In ApplicationController

class ApplicationController < ActionController::Base

      rescue_from ActiveRecord::RecordNotFound,    with: :route_not_found
      rescue_from ActionController::RoutingError,  with: :route_not_found
      rescue_from ActionController::UnknownFormat, with: :route_not_found


    def route_not_found
        render file: Rails.public_path.join('404.html'), status: :not_found, layout: false
      end

If you cannot easily run production mode locally, set the consider_all_requests_local to false in your config/environments/development.rb file.

This is already the default behavior in production. In development environment routing errors are displayed to let the developer notice them and fix them.

If you want to try it, start the server in production mode and check it.

$ script/rails s -e production