Messaging with RabbitMQ and AMQP
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Transcript of Messaging with RabbitMQ and AMQP
Messaging with AMQP and RabbitMQ
Eberhard Wolff Architecture and Technology Manager
adesso AG
Overview • Why Messaging, AMQP and RabbitMQ • Basic AMQP • Exchanges • More on Spring-AMQP
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 • Some products support both
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 2.8.7 • 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 1.1.2 • 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 – Scales to massive numbers of connections
Basic AMQP
Very Basic AMQP • Queues: Store messages • Queues might be
– Durable: Survive server restarts – Exclusive: For one connection – autoDelete: Deleted if connection closes
• 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 MessageConverter • Messages are binary data • RabbitTemplate uses
MessageConverter to convert between objects and messages
• E.g. JSON, Serialization, XML … • Can also send binary data if preferred
Basics of AMQP • Sending messages directly to queues is
not enough • What about e.g. pub / sub?
• Exchange: Route messages (stateless) • 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
Exchanges
Exchange: Route Messages • The type of Exchange defines the
routing algorithm • 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
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 on Spring AMQP
The MessageListener • So far: Calling receive() on
RabbitTemplate • Needed: Something that is called when
a new message appears
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
Spring's message-driven objects
• MessageListener means the receiver depends on Spring API
• Why not just a POJO?
Message-driven POJO
• Takes a POJO and makes it a MessageListener
• i.e. calls consume on Bean consume
<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");
Web Messaging
Web Messaging • Goal: Send / receive messages in the
browser • With JavaScript • I.e. JavaScript must receive message • HTML5 browser: WebSockets • Pre HTML5: long polling etc
SockJS • Unifies Web Sockets, long polling etc • Unified JavaScript API
• Server component • Can run embedded in RabbitMQ
STOMP • Simple (or Streaming) Text Oriented
Message Protocol • Very simple protocol for Message Oriented
Middleware
• STOMP over SockJS • See http://www.rabbitmq.com/blog/
2012/05/14/introducing-rabbitmq-web-stomp/
AMQP Java C# … Web Sockets
Long Polling
SockJS
STOMP JavaScript
http://127.0.0.1:55670/
JavaScript Code WebSocketStompMock = SockJS; var client = Stomp.client('http://localhost:55674/stomp'); … client.send('/topic/test', {}, data); … client.connect('guest', 'guest', function(x) { id = client.subscribe("/topic/test", function(message) { if (message.body) { alert("got message with body " + message.body) } }); });
AMQP: Topic exchange amq.topic with routing key test
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
Conclusion: Web Messaging • Simple API • Works on older browsers • Single server – also for messaging • Erlang is very well able to handle the
many connections
More • http://springsource.org/spring-amqp • Also a .NET version available • …and support in Spring Integration • …and there is very similar Spring JMS support • http://blog.springsource.com/2011/04/01/routing-
topologies-for-performance-and-scalability-with-rabbitm
• https://github.com/zanox/rabbiteasy – CDI event / AMQP integration – Managed publisher and consumer