config.ru

require 'action_controller'
require 'action_dispatch'
require 'action_dispatch/middleware/static'

use ActionDispatch::Static, 'public'

run lambda { |env|
 [
   200,
    {
      'Content-Type'  => 'text/html',
      'Cache-Control' => 'public, max-age=86400'
    },
    File.open('public/index.html', File::RDONLY)
  ]
}