AMQP Messaging Guide

Advanced Messaging with AMQP
Dave Syer, SpringSource, 2011

Agenda
● Overview of AMQP
● Example use cases
● What makes AMQP different?
● Comparison with JMS
● Spring AMQP

What is Messaging?

What can I use Messaging for?
How does AMQP help?

What is Messaging?

What is a Messaging Protocol?
What is it not?

Messaging Use Cases

Things a Message Broker Can Do
● Work distribution
● Pipelining
● Store-and-forward of messages
● Absorbing spikes of activity (again, decoupling)
● Routing to different consumers based on message properties

Messaging Use Cases

Patterns:
● spatial decoupling (aka communication)
● temporal decoupling (aka buffering)
● logical decoupling (aka routing)
Promote: flexibility, resilience, performance, and scale
Conclusion: There is an enormous range of applications and
problems to which messaging is an effective solution.

AMQP

AMQP = Advanced Message Queueing
Protocol

Why AMQP?

AMQP is Especially Nice Because
● All resources are dynamically created and destroyed by clients as
they need them – no static pre-configuration
● A clean and simple model: just three key nouns to learn
● Open standard, developed by the AMQP Working Group (VMware is
a member)
● Lots of client libraries available in many languages, for free
● An excellent, freely available, open source broker implementation,
called RabbitMQ.

AMQP 101

Advanced != Complicated

Create an exchange...

X

“my_exchange”
type = fanout

AMQP 101


...create a queue...

X

“my_exchange” “my_queue”
type = fanout

AMQP 101


...add a binding...

X

type = fanout

AMQP 101


...all inside a broker...

X

type = fanout

AMQP 101


...publish a message...

X

type = fanout

AMQP 101


...message sits in queue.

X

type = fanout

AMQP 101


Publish another message...

X

type = fanout

AMQP 101


...it also sits in queue.

X

type = fanout

AMQP 101


Consumer retrieves messages in order...

X

type = fanout

AMQP 101

With no binding, the message is discarded
(producer can ask to be notified)

X

type = fanout

AMQP 101


Publish several messages...
E
D
C
B
A
X

type = fanout

AMQP 101

and they are distributed amongst consumers
on the same queue...

D A
X E B

C
type = fanout

AMQP 101

Let's create another queue and bind it to
the same exchange...

X
“my_queue”

“my_exchange”
type = fanout “your_queue”

AMQP 101


..with a fanout exchange...

B
A
X
“my_queue”

“my_exchange”

AMQP 101


..all messages go to every queue...

X B A
“my_queue”

“my_exchange” B A

AMQP 101


...and can be consumed...

A
X B
“my_queue”

“my_exchange” B A

AMQP 101


...at different rates...

A
X B
“my_queue”

“my_exchange”
type = fanout “your_queue” B A

AMQP 101


...depending on the consumer, network and broker

B A
X
“my_queue”

“my_exchange”
type = fanout “your_queue” B A

AMQP 101


Let's change the exchange to be a direct type...

X
“my_queue”

“my_exchange” “your_queue”
type = direct

AMQP 101


...then the bindings have to have a key...

bk = “vodka”
X
bk “my_queue”
= “be
er”

type = direct

bk = Binding Key

AMQP 101


...and the messages have to have a routing key...

rk = “vodka”

bk = “vodka”
X
bk “my_queue”
= “be
er”

type = direct

rk = Routing Key
bk = Binding Key

AMQP 101

...a direct exchange matches the
routing key to a binding key...
rk = “beer”

bk = “vodka”
X
bk “my_queue”
= “be
er”

type = direct

rk = Routing Key
bk = Binding Key

AMQP 101

...a direct exchange matches the
routing key to a binding key...

bk = “vodka”
X
bk “my_queue”
= “be
er”

type = direct

rk = Routing Key
bk = Binding Key

AMQP 101


...messages with no matching binding...

rk = “tequila”

bk = “vodka”
X
bk “my_queue”
= “be
er”

type = direct

rk = Routing Key
bk = Binding Key

AMQP 101


...are discarded

bk = “vodka”
X
bk “my_queue”
= “be
er”

type = direct

rk = Routing Key
bk = Binding Key

AMQP 101


Let's change the exchange to be a topic type...

X
“my_queue”

type = topic

AMQP 101


...permits wildcard in bindings...

bk = “a.*.c”
X
bk “my_queue”
= “#.
e”

type = topic

bk = Binding Key

AMQP 101

Binding keys are period(.)-separated:
* matches 1 element
# matches 0 or more elements

rk = “a” A bk = “a.*.c”
rk = “a.b” X
B bk
= “my_queue”
rk = “a.b.c” C “#.
e”
rk = “a.e” D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

rk = “a” X
A bk = “a.*.c”
rk = “a.b” X
B bk
= “my_queue”
rk = “a.b.c” C “#.
e”
rk = “a.e” D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

bk = “a.*.c”
rk = “a.b” X
B bk
= “my_queue”
rk = “a.b.c” C “#.
e”
rk = “a.e” D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

bk = “a.*.c”
X
rk = “a.b” X
B bk “my_queue”
rk = “a.b.c” = “#.
C e”
rk = “a.e” D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

bk = “a.*.c”
X
bk “my_queue”
rk = “a.b.c” = “#.
C e”
rk = “a.e” D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

bk = “a.*.c”
X C
bk “my_queue”
= “#.
e”
rk = “a.e” D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

bk = “a.*.c”
X C
bk “my_queue”
= “#.
e”
D
rk = “a.b.e” E
type = topic

rk = Routing Key
bk = Binding Key

AMQP 101

* matches 1 element

bk = “a.*.c”
X C
bk “my_queue”
= “#.
e”
E D
type = topic

rk = Routing Key
bk = Binding Key

Other Stuff the AMQP Broker Does

Yes, all the standard things
● Errors can be raised for messages that do not get routed to any
queues
● Messages can be consumed so that the broker does not forget about
the message until the client explicitly acknowledges the message
● Messages can be published with a property indicating whether the
message should be written to disk
● Transactions: making publication and acknowledgement of several
messages atomic
● Flow control: e.g. used to stop publishers from overwhelming the
broker in extreme situations

Conclusion: Why AMQP?

An Open Protocol has some advantages...
● Makes it easier to have multiple implementations that interoperate at
the wire-level
● Avoids vendor lock-in: easy to rip out and replace individual
components with alternative implementations
● Allows third-parties to write client libraries for other languages
● Decouples flag-day upgrades for both client libraries and broker
● Allows third-party traffic analysis tools to inspect and decode
interactions between the clients and brokers
● Promotes similarities in APIs presented by different client libraries

Introducing RabbitMQ

RabbitMQ, AMQP and Messaging
● RabbitMQ consists of the broker (server) and several clients
● (Java, .Net, plus others)
● They speak the AMQP protocol to each other
● Anyone can write (and many have) other clients which also speak
AMQP and work with RabbitMQ
● RabbitMQ is freely available and open source, licensed under the
Mozilla Public License v1.1
● It’s already in many popular Linux distributions (Ubuntu, Debian,
Fedora, Gentoo) and can be easily installed on OS X both through
MacPorts and Homebrew

AMQP and JMS

How does AMQP compare to JMS?
When would I use one or the other?

AMQP and JMS

AMQP JMS
Protocol API
No language Java
Industry committee, mainly finance JEE
Interoperability from client libraries Interoperability from proprietary
features
Resources can be managed by clients Resources often centrally managed
Not ubiquitous in enterprise Ubiquitous through JEE
Flexible usage patterns, emphasise Two basic producer patterns (Queue
routing and Topic)
Designed for large numbers of Hard to manage large numbers of
queues and exchanges Destinations

AMQP and JMS

 JMS
• standard in the Java space
• lots of open source options
• provided with Java EE application servers
• Spring JMS

Java producers Message broker Java consumers

C
P queue

C

P queue
C

JMS

 Sending JMS Messages
• Inject an instance of Spring's JmsTemplate.
• Provide the JMS ConnectionFactory in the JmsTemplate bean definition.
@Component
public class MessageSender {
@Autowired
private volatile JmsTemplate jmsTemplate;

public void send(String message) {
this.jmsTemplate.convertAndSend("example.queue", message);
}
@Bean public ConnnectionFactory cf (){
} return new CachingConnectionFactory(...);
}
@Bean public JmsTemplate template(){
return new JmsTemplate(this.cf()) ;
}

AMQP and JMS

●
AMQP
• real standard
• a product of the the companies with the most mission critical requirements
• Spring AMQP
AMQP producers exchanges Message broker AMQP consumers

C
P X queue

C

P X queue
C

Spring AMQP

● Java and .NET
● AMQP core abstraction plus RabbitMQ implementation (built on
rabbit client libraries)
● Higher level patterns for clients: admin, producers and consumers
● ConnectionFactory – extra abstraction on top of Rabbit client (e.g. for re-
connection)
● RabbitAdmin – declare exchanges, queues, bindings
● RabbitTemplate – convenience methods for send and receive
● MessageListenerContainer – POJO message handler, asynchronous
● Spring Integration support
http://www.springsource.org/spring-amqp

Spring AMQP: RabbitTemplate

public class MyComponent {
private RabbitTemplate rabbitTemplate;

public MyComponent(ConnectionFactory connectionFactory) {
this.rabbitTemplate = new RabbitTemplate(connectionFactory);
}

public void read() throws Exception {
...
String value = rabbitTemplate.receiveAndConvert("myQueueName");
...
}

}
Convenience methods

Spring AMQP: SimpleMessageListenerContainer

● Asynchronous message receiver
● POJO handlers
● Handles re-connection and listener failure (rollback, redelivery)
● Message conversion and error handling strategies

<listener-container connection-factory="connectionFactory">
<listener ref="handler" method="handle" queue-names="my.queue">
</listener-container>

AMQP Messaging Guide

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