How to configure mariadb-galera cluster and rabbitmq cluster on separate set of node from the controller via Director

Issue

• Presently when deploying overcloud via Director, it installs mariadb-galera cluster and the rabbitmq cluster on the controller nodes. However this solution is not scalable as I cannot segregate the load on database, messaging from the controller.

• The use case is that in a large scale deployment, running mariadb-galera cluster + rabbitmq-cluster + all API, glance, cinder, other management services etc. on 3 controllers will be causing performance challenges on these controller nodes. Also, due to large scale - if controller nodes need to be scaled up to handle higher number of API requests + glance and so on, we cannot scale up only controller services without additional database / rabbitmq [as these services are currently tied up with the controller node role / profile]

• To avoid such a situation and to be able to scale controller services independently of database / rabbitmq, I want to know the method to do so via director.