emqx presumably wasn't used because they are a Java shop and emqx is written in Erlang. Apparently they have a need for a massive scaling MQTT broker. At that p

emqx presumably wasn't used because they are a Java shop and emqx is written in Erlang. Apparently they have a need for a massive scaling MQTT broker. At that point you need to be seriously comfortable with the tools you are using. Whether that's Java, Rust, Erlang, C#, C++ or whatever. Using an existing application in a language/ecosystem your team is not experts in is probably going to be a problem unless you seriously invest in the new language/ecosystem first. And it's going to take at least something like a thousand hours to really become good at something. The other option is writing an alternative in the language you are already familiar with. So in that regard I can understand why they did it. I guess they could have used the OSS HiveMQ version as a base though. No idea why they didn't do that.