Storm High Availability and Failover - Real-time Analytics with Storm and Cassandra - page 89

An overview of RabbitMQ
The punch line that goes for RabbitMQ is Messaging that just works .
RabbitMQ is one of the most widely used implementations of the AMQP messaging pro-
tocol that provides a platform for message receipt and delivery. This in-memory queue also
has the capacity to hold and retain messages till they are consumed by a consumer. This
flexible brokering system is very easy to use and works on most of the operating systems
such as windows, UNIX, and so on.
RabbitMQ is an implementation of the Advanced Message Queuing Protocol ( AMQP ).
As depicted in the following figure, the vital components of RabbitMQ are exchange and
Queue :
The publisher and the consumer are two essential actors; the former generates the messages
and publishes them to the exchange, which in turn (depending upon its type) publishes the
message from the publisher to the queue and from the queue to the consumer, who picks up
the message.
The point to note is that here the publisher interacts with the exchange and not the queue.
There are various kinds of exchanges that RabbitMQ supports such as direct, fanout, topic,
and so on. The task of the exchange is to route the message to one or more queues depend-
ing upon the type of exchange and the routing key associated with the message. So if it's a
direct exchange, the message will be delivered to one queue bound to the exchange with
the routing key matching the one in the message. If it's a fanout exchange, then the message
is delivered to all the queues bound to the exchange, and the routing is totally ignored.