How do I redirect to root - public/index.html?

You can assign a named route to a static file by passing any non-empty string as :controller and the path to the file as the :action for the route:

Application.routes.draw do

  root :controller => 'static', :action => '/' 
  # or
  # root :controller => 'static', :action => '/public/index.html'

end

# elsewhere

redirect_to root_path # redirect to /

Assuming you have a public/index.html, this is what will be served.

route file:

     root 'main#index'

controller:

     class MainController < ApplicationController
       def index
         redirect_to '/index.html'
       end
     end

and using rails 4 controller action live this can behave like a single page application using the M & C with a twist on the V

on controller

 redirect_to root_path ## (will redirect to root '/')