4.2 Message Broker
Rabbitmq is the one chosen for this role. Services are communicating with each other either by publishing message or by consuming messages to/from a declared queue.
For NM2 deployment a cluster of 3 instances of Rabbitmq is deployed for High Availability, where queues are mirrored through all members. Actual connections handling is performed by the cluster's master and in case it fails, a new master is elected among members.