Allow 2 ovelray network to communicate with each other

i am wondering in docker swarm

  • how to allow containers existing on 2 different overlay networks to communicate with each other, without having to put these containers on the same overlay network. i am asking because rancher allow inter-overlay network communications.
  • how to disable communications between the containers of just a specifc service not all the services

my case is
i have the service sftp and i need the containers of this service to be able to communicate with all services HTTPD.
each service HTTPD exists on its own network, because, for security reasons, i don’t want the services HTTPD to communicate with each other.
so i cannot put all the HTTPD services on same network with the SFTP service as they will be able to communicate with each other, so i need to allow the containers of the service SFTP and that resides on their own network , to be able to communicate with the networks of all the HTTPD services

i hope i was clear enough
your help would be appreciated