Example of how to dispatch requests from 1 Rack application out to different Rack apps

config.ru

apps = {
  'localhost.first' => ->(env) { [200, {'Content-Type' => 'text/plain'}, ['App 1']] },
  'localhost.second' => ->(env) { [200, {'Content-Type' => 'text/plain'}, ['App 2']] }
}

run ->(env) do
  request = Rack::Request.new(env)

  if app = apps[request.host]
    app.call(env)
  else
    [404, {'Content-Type' => 'text/plain'}, ["No app found for host: #{request.host}"]]
  end
end