Housecat is a one-to-one messaging pattern in which a sender addresses a receiver by name. The diagram shows this pattern, where Master refers to the sender, and Cat refers to the receiver. The Router refers to a set of feeds and pipes, or other resources capable of queuing and routing messages.
In the general decoupled messaging model, the cat reads from a private queue which subscribes to the named address, and the master publishes messages to this named address. In a coupled model, the cat reads from a named queue and the master publishes into this queue directly.
Housecat, or rather its variation Reverse Housecat is most commonly used as part of a request-response scenario, to define a path for replies to a service request.
Housecat scales to many masters, a variation called Multimaster Housecat. Decoupled Housecat can be used with multiple cats, each of which will get a copy of the message.