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The Future of Messaging: RabbitMQ and AMQP
1. The Future of Messaging:
RabbitMQ and AMQP
Eberhard Wolff
Architecture & Technology Manager
adesso AG, Germany
2. About me
• Eberhard Wolff
• Architecture & Technology Manager at adesso
• adesso is a leading IT consultancy in Germany
• Speaker
• Author (i.e. first German Spring book)
• Blog: http://ewolff.com
• Twitter: @ewolff
• eberhard.wolff@adesso.de
4. RPC
• Predominant approach
– RMI, SOAP Web Services, CORBA, HttpInvoker,
Burlap, Hessian
• Calls remote methods with parameter
• …and waits for response
• Problems:
– Explicitly tells the server what to do i.e. tight
coupling
– What about network failures?
– What about long latencies?
5. Why Messaging?
• Decoupling
– Data, no action i.e. receiver
Component
can react arbitrarily
– Asynchronous i.e. decoupled
by time
• Reliable
– Message can be stored-and-
Component
forwarded
Messages
– Redelivery until message
processed
• Solves typical problems of
distributed systems
6. Why Messaging?
• But: Requires different architecture
• Very different from calling remote methods
• Asynchronous
• AJAX has the same model
• See for example “Patterns of Enterprise
Integration”
7. Why AMQP?
• Open standard protocol
• Standard wire protocol
• i.e. just one client library – no matter which
implementation you are using
• Less vendor lock in
• Efficient
– Binary wire protocol
• Support in all major languages
• Supported on most OS platforms
8. What about JMS?
• JMS has been the default for Java messaging
system for 10+ years
• But:
• Only standardized on the API level
• Less flexible than AMQP
• Mapping AMQP/JMS is being defined
• There is
git://github.com/pieterh/openamq-jms.git
9. Why Rabbit?
• Because it has a kewl name
• Numerous protocols supported
• Most popular choice on EC2
• Foundation for demanding systems e.g.
NASA’s cloud initiative Nebula
• Implemented in Erlang
• Clustering built in
• Currently in 2.4.1
• Supports AMQP 0.8, 0.9, 0.9.1
11. Broad Support in the JVM Space
• Grails Plug In
• Java Client
• Scala / Lift support
• We will discuss Spring support in detail
• Spring AMQP project 1.0.0.RC1
• http://www.springsource.org/spring-amqp
12. Why Erlang?
• Originally designed for telephone
switches by Ericsson
• Much easier to develop scalable and fault
tolerant systems (by factors)
• See Motorola presentation:
http://www.slideshare.net/Arbow/comparing-
cpp-and-erlang-for-motorola-telecoms-
software
• Good tool for reliable and scalable systems
13. Erlang‘s Model
Monitor
Link to monitor,
restart
Light Light Light
weight Messages weight Messages weight
process process process
with with with
state state state
14. Why Erlang?
• Let it crash
– If a process fails, it can be easily restarted
– Different approach to fault tolerance
– Otherwise lots of error handling
• Message Passing in the Core
– RabbitMQ is a messaging system…
• Light-weight process model
– Scalabiliy
15. Very Basic AMQP
• Queues: Store messages
• Queues might be
– Durable: Survive server restarts
– Exclusive: For one connection
– autoDelete: Deleted if connection closes
• Queue usually created by consumer
• All resources are dynamic
• Producer sends a message to a Queue
• Let’s see some code…
16. Spring’s RabbitTemplate
• Send & receive message
• AmqpTemplate: Generic AMQP interface
• RabbitOperations: Rabbit specific interface:
(adds just a callback)
• RabbitTemplate: Implementation
• Spring might provide support for other AMQP
implementations later
• Common interface
17. Spring’s MessageConverter
• Messages are binary data
• RabbitTemplate uses MessageConverter
to convert between objects and messages
• Can also send binary data if preferred
• Default: SimpleMessageConverter
– byte[] directly transferred
– String converted with configurable encoding
– Serializable are serialized
– Content type set accordingly
• JsonMessageConverter converts from / to JSON
using Jackson
• MarshallingMessageConverter converts from / to XML
using Spring's OXM mapping
18. Spring‘s AdminTemplate
• Main purpose: Configure the AMQP
infrastructure
• E.g. create queues
• AmpqAdmin: Generic AMQP interface
• RabbitAdmin: Rabbit specific
19. Code
ConnectionFactory conFactory =
new SingleConnectionFactory("localhost");
RabbitTemplate template =
new RabbitTemplate(conFactory);
RabbitAdmin admin = new RabbitAdmin(conFactory);
admin.declareQueue(new Queue("myQueue"));
template.convertAndSend("myQueue", "Hi AMQP!");
String receive =
(String) template.receiveAndConvert("myQueue");
Assert.assertEquals("Hi AMQP!", receive);
20. Basics of AMQP
• Sending messages directly to queues is not
enough
• What about e.g. pub / sub?
• Exchange: Route messages (stateless)
• Messages are byte-streams
• Example used the default exchange
• More dynamic, flexible and cleaner than JMS
21. AMQP
in
a
nutshell
Exchange routes message
Stateless
Usually created by producer
No queue: Message discarded
X
Binding binds an
Exchange to a Queue Queues buffer
messages
Usually created by
consumer
22. AMQP
in
a
nutshell
Producer and Consumer might be written in Java, C#,
Python, Ruby …
C
P X
C
AMQP RabbitMQ AMQP
protocol protocol
23. Exchange: Route Messages X
• The type of Exchange defined the routing
algorithm used
• Binding provides selector for routing
• Exchange is addressed by name
• Some standard types
• Can provide additional ones
24. Fanout Exchange X
• Broadcast to all bound queues
• Fast
• Simple
• amq.fanout is mandatory
• To broadcast information
27. Direct Exchange X
• Routing based on one routing key
• amq.direct and the default Exchange (no
name) always exist
• To send work orders to a specific worker
29. Queue directQueue = new Queue("direct");
admin.declareQueue(directQueue);
admin.declareBinding(BindingBuilder
.from(directQueue)
.to(new DirectExchange("amq.direct"))
.with("helloKey"));
template.setExchange("amq.direct");
template.convertAndSend("amq.direct","dropMe",
"I will be dropped!");
template.convertAndSend("amq.direct","helloKey",
"Hi Direct!");
Assert.assertEquals("Hi Direct!",
template.receiveAndConvert("direct"));
Assert.assertNull(
template.receiveAndConvert("direct"));
30. Topic Exchange X
• Routing based on routing pattern
• amq.topic is mandatory
• E.g. for public / subscribe scenarios
31. Topic Exchange
order.DE
invoice.USD
Topic
Exchange
order.*
P X C
invoice.*
C
32. Headers Exchange X
• Routing based on one or more headers and
an expression
• amqp.match is mandatory
• Complex routing roles
33. Other Features
• Message can be persistent
• Request / response using correlations
possible
• Redelivery / acknowledgement possible
• Clustering with e.g. Linux HA possible
• ...or send message through multiple channels
and drop duplicates
35. Configuring Rabbit Resources with
Spring
• Spring enables decoupling of your application
code from the underlying infrastructure
• The container provides the resources
• The application is simply coded against the
API
37. Defining a RabbitTemplate Bean
• Provide a reference to the ConnectionFactory
• Optionally provide other references
– MessageConverter
– Routing key and exchange to be used if none is
specified
<bean id="rabbitTemplate"
class="org.springframework.amqp.rabbit.core.RabbitTemplate">
<constructor-arg ref="connectionFactory" />
<property name="routingKey" value=”invoice.USD" />
</bean>
38. The MessageListener
• So far: Calling receive() on RabbitTemplate
• Needed: Something that is called when a new
message appears
• The API defines this interface for
asynchronous reception of messages
public void onMessage(Message) {
// handle the message
}
39. Spring’s MessageListener
Container
• Spring provides lightweight containers to call
MessageListeners
• SimpleMessageListenerContainer
• Advanced scheduling and endpoint
management options available
• i.e. thread pools, concurrent consumers,
transaction handling
40. Defining a Message Listener
Container
<bean class="org.sfw.amqp.rabbit.listener.SimpleMessageListenerContainer">
<property name="connectionFactory" ref="connectionFactory" />
<property name="queueNames" value="my.amqp.queue" />
<property name="messageListener" ref="messageListener" />
</bean>
• Every time a new message appears on
my.amqp.queue the messageListener is
called
41. Spring's message-driven objects
• MessageListener means the receiver
depends on Spring API
• Why not just a POJO?
• MessageListenerAdapter takes a POJO and
makes it a MessageListener
• i.e. calls consume on Bean consumer
<bean id="messageListenerAdapter"
class="org.sfw.amqp.rabbit.listener.adapter.MessageListenerAdapter">
<property name="delegate" ref="consumer" />
<property name="defaultListenerMethod" value="consume" />
<property name="messageConverter" ref="jsonMessageConverter" />
</bean>
42. Easier Using Namespaces
<rabbit:listener-container
connection-factory="connectionFactory“
message-converter="jsonMessageConverter">
<rabbit:listener ref="consumer" method="consume"
queue-names="my.amqp.queue2" />
</rabbit:listener-container>
• Results in the same Spring Beans
43. Consumer code
@Component
public class Consumer {
public String consume(String message) {
return …;
}
}
• No dependency on AMQP!
• But: What about the result of the method?
• Send to the Reply-To address given in
message properties with same correlationId
as original method
44. Client Code
String response = (String)
rabbitOperations.convertSendAndReceive(
"my.fanout", "", "test");
• Message sent to destination with routing key
• Reply-To set to exclusive, autodelete, non-
durable queue
• Response received through Reply-To
converted and returned
• Easy request-response!
• Beware of potential latency
45. Create Environment
Using Namespaces
<rabbit:fanout-exchange name="my.fanout2">
<rabbit:bindings>
<rabbit:binding queue="my.amqp.queue2" />
</rabbit:bindings>
</rabbit:fanout-exchange>
<rabbit:queue name="my.amqp.queue2" />
• ...if you don‘t like API calls
47. Conclusion: Spring AMQP
• Easy to use
• Flexible (e.g. message encoding)
• Allows scalable message handling
• Full support for AMQP and RabbitMQ
48. More
• http://springsource.org/spring-amqp
• Also a .NET version available
• …and support Spring Integration
• http://blog.springsource.com/2011/04/01/
routing-topologies-for-performance-and-
scalability-with-rabbitm
• Transaction support
• …and there is very similar JMS support
