Hello devopssysadmin,
Docker internally switches requests to available replicas of a specific service in a swarm cluster.
However, in your docker-compose(stack) file as I read it, it seems that you declared thee times the same services. I assumed it is because of your constraints. But the whole idea of the swarm cluster is to manage the load balancing of each service.
In my opinion, it is better to declare your service once with some constraints and update your node accordingly by adding labels and so on.
Best Regards,
Fouscou