Wolf Call is a messaging pattern for service presence detection in which a client verifies whether or not a service is present. The diagram shows this pattern, where Caller refers to the client, and Wolf refers to the service instance or instances. The Router refers to a set of feeds and pipes, or other resources capable of queuing and routing messages.
Wolf Call is an aspect of Wolfpack and is always decoupled. The wolves read from a shared queue named for the service, and the caller checks for the presence of this named queue.
The RestMS 4/AMQP9 profile implements Wolf Call through the service and rotator feed types.