There's no need for asynchronous code and new frameworks to achieve that. Comsat makes Dropwizard run simple blocking requests in Quasar fibers (I'm a Quasar/Comsat dev), so you get all the performance of async code while still working with simple blocking code, standard APIs (JAX-RS), and standard servers (Jetty). You can easily run a hundreds-of-thousands if not millions of fibers in a single JVM without getting into trouble.