Oh Vert.x, I despise it. We jumped on that in 2014 (Vert.x 2) and it's still haunting us. Half-broken build with an outdated Gradle plugin (should've stuck with the official build system), doesn't integrate with the major part of the Java ecosystem due to being callback-based (exceptions can hardly be used, nor can anything that blocks on IO) and tooling for managing tasks doesn't exist either (e.g. running a couple of IO-tasks in order requires you to nest the callbacks if you don't write your own tooling).

I assume Vert.x 3 is doing a better job there, but the fundamental problem remains: callbacks don't work well with exceptions. Maybe Kotlin helps wrapping this nicer, I don't know. All I know is that I'll be more careful when selecting a framework for productive use now. And maybe that I won't be using Vert.x again.