Architecture | The Future of Messaging: RabbitMQ and AMQP | Eberhard Wolff

The Future of Messaging:
RabbitMQ and AMQP
Eberhard Wolff
Architecture and Technology Manager
adesso AG, Germany

Overview
•  Why Messaging, AMQP and RabbitMQ
•  Basic AMQP
•  Exchanges
•  More on Spring-AMQP

RPC
•  Predominant approach
–  RMI, SOAP Web Services, CORBA,
HttpInvoker, Burlap, Hessian
•  Calls remote methods with parameter
•  …and waits for response

RPC
•  Problems:
–  Explicitly tells the server what to do i.e.
tight coupling
–  What about network failures?
–  What about long latencies?

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

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”

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

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

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 2.6.1
•  Supports AMQP 0.8, 0.9, 0.9.1
•  1.0 as a prototype Plug In

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
•  http://www.springsource.org/spring-
amqp

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

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

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

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

Code
ConnectionFactory conFactory =
new CachingConnectionFactory ("localhost");
RabbitAdmin admin = new RabbitAdmin(conFactory);
admin.declareQueue( 
new Queue("myQueue", false, true, true));

RabbitTemplate template =
new RabbitTemplate(conFactory);
template.convertAndSend("myQueue", "Hi AMQP!");
String receive =
(String) template.receiveAndConvert("myQueue");
Assert.assertEquals("Hi AMQP!", receive);

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

Spring’s MessageConverter
•  Messages are binary data
•  RabbitTemplate uses
MessageConverter
to convert between objects and
messages
•  Can also send binary data if preferred

Spring’s MessageConverter
•  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
•  SerializerMessageConverter uses Spring’s
Serializer abstraction

Spring‘s AdminTemplate
•  Main purpose: Configure the AMQP
infrastructure
•  E.g. create queues

•  AmpqAdmin: Generic AMQP interface
•  RabbitAdmin: Rabbit specific

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

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

AMQP
in
a
nutshell

Producer and Consumer might be written in Java, C#,
Python, Ruby …

C
P X

C

AMQP RabbitMQ AMQP
protocol protocol

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

Fanout Exchange X

•  Broadcast to all bound queues
•  Fast
•  Simple

•  amq.fanout is mandatory

•  To broadcast information

Fanout Exchange X

C
P X

C
Fanout
C

Queue fanoutQueue = new Queue("fanoutQueue");
admin.declareQueue(fanoutQueue);

FanoutExchange fanoutExchange=
new FanoutExchange("myFanout");
admin.declareExchange(fanoutExchange);

admin.declareBinding(
BindingBuilder.bind(fanoutQueue).
to(fanoutExchange));

template.setExchange("myFanout");
template.convertAndSend("Hi Fanout!");

String receive = (String)
template.receiveAndConvert("fanoutQueue");
Assert.assertEquals("Hi Fanout!", receive);

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

Direct Exchange

normal
express
Direct
Exchange C
express
P X

C
normal
C

Queue directQueue = new Queue("direct");
admin.declareQueue(directQueue);

admin.declareBinding(BindingBuilder
.bind(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"));

Topic Exchange X

•  Routing based on routing pattern
•  amq.topic is mandatory

•  E.g. for public / subscribe scenarios

Topic Exchange

order.DE
invoice.USD
Topic
Exchange
order.*
P X C

invoice.*
C

Headers Exchange X

•  Routing based on one or more headers and
an expression
•  amqp.match is mandatory

•  Complex routing roles

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

More about
RabbitMQ and Spring

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

Configuring a
ConnectionFactory
Create an object
with the given name
and class
<bean id="connectionFactory" Call setUsername()
with the given value
class="org.sfw.amqp.rabbit.connection.CachingConnectionFactory">
<property name="username" value="guest"/>
<property name="password" value="guest"/>
<constructor-arg value="localhost" />
</bean>
Parameter for the
constructor

•  Can easily modify configuration options

Using a ConnectionFactory
from Cloud Foundry
<cloud:rabbit-connection-factory
id="rabbitConnectionFactory" />

ConnectionFactory connectionFactory =
new RabbitServiceCreator(new CloudEnvironment())
.createSingletonService().service;

•  Will be provided by Cloud Foundry

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>

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 interface MessageListener {
public void onMessage(Message) {
// handle the message
}
}

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

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

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>

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

@Component Consumer code
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

Client Code
String response = (String)
rabbitTemplate.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

Create Environment using
Namespaces
•  ...if you don‘t like API calls
<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" />

<rabbit:admin connection-factory="rabbitConnectionFactory" />

New Elements
•  Links: unidirectional transport between
source and target
–  Flow control
–  Settling transfers for different semantics (at
most once etc)
•  Processing nodes have distribution
modes
–  Copy: Copy message to each link
–  Move: Move it to just one link

AMQP: Point to Point
Incoming
Link Receiver

Node
Sender mode : Receiver
Outgoing move Incoming
Link Link

Broker

AMQP: Publish / Subscribe
Incoming
Link Receiver

Node
Sender mode : Receiver
Outgoing copy Incoming
Link Link

Broker

Conclusion: AMQP
•  Ubiquitous Messaging
•  AMQP: Protocol standard
•  Better scalability
•  Dynamic resources

Conclusion: Spring AMQP
•  Easy to use
•  Flexible (e.g. message encoding)
•  Allows scalable message handling
•  Full support for AMQP and RabbitMQ

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

Architecture | The Future of Messaging: RabbitMQ and AMQP | Eberhard Wolff

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