Zuul VS Quasar

What's important is that Zuul gates your codebase, whereas other tools sometimes let faulty commits go through. Unfortunately there's a bit of a name collision with Netflix Zuul gateway service, but that's awesome F/OSS for another day.

Automatic load balancing — You might have used Netflix Zuul for this.

Check this one - https://github.com/Netflix/zuul

Java 21 doesn't retrofit green threads though. Quasar [0] is a library that implemented fibers for Java and the main developer pron has joined the OpenJDK development team. All that was necessary for first party support is to make the JDK libraries yield when blocking.

Adopting async isn't impossible at all, there is very little demand for it.

[0] https://docs.paralleluniverse.co/quasar/

Third party options have been around for nearly a decade now: https://docs.paralleluniverse.co/quasar/

Quasar Fiber (https://docs.paralleluniverse.co/quasar/) is the equivalent implementation of goroutine in Java.

Even Loom architect Ron Pressler had something else in mind with his earlier prototype Quasar, with a spaceship demo.

I'd say because of Erlang. Loom's architect was building a bytecode-modifying (with a javaagent) lib named Quasar before he joined Oracle. The project page mentions a news titled "Introductory blog post: Erlang (and Go) in Clojure (and Java), Lightweight Threads, Channels and Actors for the JVM." in May 2, 2013.