The document discusses the concepts and implementation of message brokers in service-oriented architecture, detailing synchronous and asynchronous service invocations. It covers the publisher-subscriber pattern, the benefits of decoupling, and various message broker standards like JMS, MSMQ, and AMQP. The document also compares JMS and AMQP, highlights two WS specifications (WS-Eventing and WS-Notification) used for implementing the publisher-subscriber model, and addresses potential differences between ESB and message brokers.

1. ICTA Technology Meetup 12ICTA Technology Meetup 12
By Crishantha Nanayakkara
Message Brokers

2. Service Invocation
●
Synchronous
– The consumer uses a single thread to invoke
the service. The thread sends the request,
blocks it until it gets the response from the
service
●
Asynchronous
– The consumer uses a pair of threads to invoke
the service. The first thread sends the request
and releases itself. The second thread gets the
response from the service once it completes
its task.

3. Synchronous – RPC Style
●
The predominant approach
– RMI, SOAP / REST Web Services, CORBA
●
Request/Response pattern
– Calls remote methods and waits for the
response
●
Problems
– Tight coupling
– What about network failures or long latencies?

4. Asynchronous – Messaging Style
●
Decoupled
●
Reliable
– Message can be stored and forwarded
– Redelivery until the message processed
●
Solves typical problems of distributed systems
– Network Failures
– Network Latency issues

5. Asynchronous – Messaging Style

6. Asynchronous – Messaging Style
●
Broadcast Oriented – All messages goes to all
applications
●
Point­point – All messages goes to one
application
●
Subscription based – All messages goes only to
subscribers

7. Messaging is used in distributed
computing to achieve asynchronous
communication

8. Notification and Eventing
Source: Service Oriented Architecture, Concepts, Technology and Design, Thomas Erl

9. Publisher Subscriber Pattern

10. Publisher Subscriber Pattern
●
This involves a publisher service that makes
information categorized by different topics for
registered subscribers.
●
Subscribers can select which that they are willing to
subscribe by interacting directly with a publisher.
●
Here, When a new piece of information on a given
topic is available, the publisher broadcasts this
information to all those subscribers/ services that
have subscribed to that topic.

11. Why Message Brokers?

12. Using a Message Broker

13. Using a Message Broker
●
A message broker can be used to perform the
broadcast on the publishers’ behalf.
●
Reduce the dependency between the publisher and
the subscriber allowing it for a complete decoupled
architecture.
●
Provides the much required flexibility and the
scalability.

14. 14
Message Broker Standards and
Implementations
●
The Message Broker protocols / standards:
– JMS (A Java standard)
– MSMQ (.NET implementation)
– AMQP (An open standard)
●
Implementations:
– Apache ActiveMQ (JMS)
– .NET WCF (MSMQ)
– RabbitMQ (AMQP)
– Apache Qpid (AMQP)
– ZeroMQ (AMQP)

15. 15
JMS
●
JMS is a Java API that allows applications to
create, send, receive and read messages.
●
JMS API defines a common set of interfaces
and associated semantics that allow programs
written in Java to communicate with other
messaging implementations.

16. 16
Advanced Message Queuing Protocol
(AMQP)

17. 17
AMQP
●
AMQP (Advanced Message Queuing Protocol)
is an open standard and a wire­level protocol,
which is designed to support messaging on
the Internet.
●
AMQP is the only open standard available so
far for the cross platform interoperability
between heterogeneous messaging systems
and message brokers.

18. 18
AMQP
●
For example, Java Message Producer (JMS
Client) can send message to a .NET/C#
consumer with the help of a AMQP Message
Broker
●
it is inter­operable, reliable, open,
standardized, complete and safe

19. 19
JMS vs AMQP
●
JMS has the ability to communicate with non­Java platforms
like Ruby by using Message Bridges. But this is a bit of a
complex situation in the Enterprise level Integration.
●
The industry is using AMQP to get rid of this complexity

20. Message Brokering in SOA

21. WS­Eventing vs WS­Notification
●
There are two WS specifications to implement
the publisher subscriber pattern
– WS­Eventing (A W3C Specification)
– WS­Notification (An OASIS Specification)
●
Each one uses a different approach and a
terminology to fulfill the “same task”
●
WS­Eventing is more simpler and WS­
Notification is more detailed

22. WS­Notification
(with a broker)

23. WS­Notification
(with a broker)
●
The Notification Broker (Web Service) – Acts on
behalf of the publisher to perform the role of the
Notification Producer.
●
The Publisher Registration Manager (Web Service)
– This provides an interface for subscribers to search
through and locate items available for registration
●
The Subscription Manager (Web Service) – This
allows notification producers to access and retrieve
required subscriber information for a given
notification message broadcast.

24. WS­Notification compliant Message
Brokers
At Alpha Stage – Developed by ICTA TT

25. WS­Eventing

26. WS­Eventing compliant Message
Brokers

27. The Sample Code
●
https://docs.wso2.org/display/MB210/Web+S
ervice+Client+Sample

28. ESB Vs Message Broker
Any difference?

29. Questions ?