ceder stackバージョン。 ほぼ下記のまんまです。 Creating Static Sites in Ruby with Rack | Heroku Dev Center $ mkdir -p public/{images,js,css} $ touch site/{config.ru,public/index.html} # Gemfile: source :rubygems gem 'rack' # config.ru: use Rack::Static, urls: ['/images', '/js', '/css'], root: 'public' run lambda { |env| [ 200, { 'Content-Type' => 'text/html', 'Cache-Control' => 'public, max-age=86400' }, File.open