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 can react arbitrarily

– Asynchronous i.e. decoupled by time

•  Reliable – Message can be stored-and-

forwarded – Redelivery until message

processed •  Solves typical problems of

distributed systems

Component

Component Messages

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 RabbitMQ

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

Light weight

process with state

Monitor

Link to monitor, restart

Light weight

process with state

Light weight

process with state

Messages Messages

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

Queues buffer messages Usually created by consumer

Binding binds an Exchange to a Queue

AMQP  in  a  nutshell  

AMQP protocol

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

X

C

C

P

RabbitMQ AMQP protocol

Exchange: Route Messages

•  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

X

Fanout Exchange

•  Broadcast to all bound queues •  Fast •  Simple

•  amq.fanout is mandatory

•  To broadcast information

X

X

C

C

C

P

Fanout

Fanout Exchange X

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 •  Routing based on one routing key •  amq.direct and the default Exchange (no

name) always exist

•  To send work orders to a specific worker

X

X

C

C

C

P

Direct Exchange

express

normal

express normal

Direct Exchange

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

•  E.g. for public / subscribe scenarios

X

Topic Exchange  

X C

C

P

Topic Exchange

order.*

invoice.*

order.DE invoice.USD

Headers Exchange •  Routing based on one or more headers and

an expression •  amqp.match is mandatory

•  Complex routing roles

X

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

•  Can easily modify configuration options

<bean id="connectionFactory" class="org.sfw.amqp.rabbit.connection.CachingConnectionFactory"> <property name="username" value="guest"/> <property name="password" value="guest"/> <constructor-arg value="localhost" /> </bean>

Create an object with the given name

and class Call setUsername() with the given value

Parameter for the constructor

<cloud:rabbit-connection-factory id="rabbitConnectionFactory" />

Using a ConnectionFactory from Cloud Foundry

•  Will be provided by Cloud Foundry

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

<bean id="rabbitTemplate" class="org.springframework.amqp.rabbit.core.RabbitTemplate"> <constructor-arg ref="connectionFactory" /> <property name="routingKey" value=”invoice.USD" /> </bean>

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

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

•  Every time a new message appears on my.amqp.queue the messageListener is called

<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>

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

•  Results in the same Spring Beans

<rabbit:listener-container connection-factory="connectionFactory“ message-converter="jsonMessageConverter"> <rabbit:listener ref="consumer" method="consume"

queue-names="my.amqp.queue2" /> </rabbit:listener-container>

Consumer code

•  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

@Componentpublic class Consumer { public String consume(String message) { return …; }}

Client Code

•  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

String response = (String) rabbitTemplate.convertSendAndReceive( "my.fanout", "", "test");

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" />

A SHORT GLIMPSE ON AMQP 1.0

EVERYTHING YOU KNOW IS WRONG

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

Broker

Node mode : move

Sender Receiver Outgoing Link

Incoming Link

Receiver Incoming Link

AMQP: Publish / Subscribe

Broker

Node mode :

copy Sender Receiver

Outgoing Link

Incoming Link

Receiver Incoming Link

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

•  …and there is very similar JMS support J

Questions? @ewolff