Recently wanted to also create a cluster of mqtt brokers and found this medium tutorial stringing Docker Swarm, RabbitMQ, Consul and HAProxy together very helpful[0].

I was not happy with the static ip's for haproxy and opted to register the mqtt/tls services in consul and use the consul dns resolver with hapraxy.

[0]: https://medium.com/hepsiburadatech/implementing-highly-avail...