Messaging

Message Type Patterns Command Invoke a procedure in another application SOAP request is an example Document Message Single unit of information, single object or data structure SOAP response is an example Event Asynchronous event notification between applications Do not require a reply Request-reply Two-way communication Can be P2P or pubsub How should it be broadcasted? 1, 2, …, many?

Message Channel Patterns Channels = queues Point-to-point Channel Take out the middle man Pub-sub Channel Sends event to all subscribed users Datatype Channel Different data types have their own channels Allows applications to handle events differently based on object

Message Queuing One of the most widely used method for distributed apps Allows distributed applications to communicate asynchronously Messages sent are stored in queue to be delivered to recipient Allows abstraction Distributed applications can be developed without the need to worry about the mode of transportation Don’t care about the availability of end recipient

Message Queuing Advantages No direct communication between programs (clients) Loose coupling Communication is independent of time Communication can be driven by events Work is carried out by small self-contained programs Can assign priority to a message Security Authorization checks (like access control list) Data Integrity Recovery Support

Message Oriented Middleware (MOM) AMQP (Advanced Message Queuing Protocol) Apache Qpid RabbitMQ StormMQ XMPP (Extensible Messaging and Presence Protocol) ejabberd (Erlang Jabber Daemon) Metronome STOMP (Streaming Text Oriented Messaging Protocol) Apache ActiveMQ Apache Apollo RabbitMQ Others Apache Kafka

Example from RabbitMQ

CMAPI with Message Broker

Evaluation Strengths Provides increased modularity: middleware is swappable Can use pub/sub in browser and pub/sub across browsers Asynchronous communication model for speed Leverage distributed resources for efficiency and redundancy Weaknesses Distributed, asynchronous nature could lead to difficult debugging Complicated to program (if you start from scratch…) No real strong standards….