MESSAGE PASSING
it can act as a buffer if the recipient is unavailable or overloaded, and thus improve system reliability;
it can automatically redeliver messages to a process that crashed, and thus prevent messages from being lost;
it avoids the sender needing to know the IP address and port number of the recipient (which is particularly useful in a “cloud” deployment where virtual machines often come and go);
it allows one message to be sent to several recipients;
it logically decouples the sender from the recipient (the sender just publishes messages and doesn’t care who consumes them).
However, a difference compared to RPC is that message-passing communication is usually one-way: a sender normally doesn’t expect to receive a reply to its messages. It is possible for a process to send a response, but this would usually be done on a separate channel. This is what makes it asynchronous: the sender doesn’t wait for the message to be delivered, but simply sends it and then forgets about it.
Message brokers
