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Message Queues : A Primer - International PHP Conference Fall 2012
Mike Willbanks | Barnes & NobleMessage Queues : A Primer
Housekeeping…• Talk – Slides will be posted after the talk.• Me – Sr. Web Architect Manager at NOOK Developer – Prior MNPHP Organizer – Open Source Contributor – Where you can find me: • Twitter: mwillbanks G+: Mike Willbanks • IRC (freenode): mwillbanks Blog: http://blog.digitalstruct.com • GitHub: https://github.com/mwillbanks
Agenda• Message Queues?• Protocols and Software• Picking a Message Queue• Best Practices
A Definition“Message queues and mailboxes are software-engineeringcomponents used for interprocess communication, or for inter-thread communication within the same process. They use a queuefor messaging – the passing of control or of content.”
What is messaging?“Messaging describes the sending and receiving of data (in theform of messages) between systems. Messages are exchangedbetween programs or applications, similar to the way peoplecommunicate by email but with guarantees on delivery, speed,security and the absence of spam.”
Producer Messages Consumer Messages Task MessagesGeneral AnatomyProducer creates a message and pushes it to the queue; theconsumer reads from the queue and processes the message.
Describing Message Queuesl Pub/Subl FIFO bufferl Push / Pulll A way to communicate between applications / systems.l A way to decouple components.l A way to offload work.
Why to use a Message Queuel Offload Heavy Workl Integration with Legacy Systemsl Asynchronous Processingl Parallel Processingl Process consistencyl Scalability
Unix Foundationsl “Write programs that work together.”l “Do it in the background.”
Why it mattersl Web systems need to be geared to run things asynchronously.l Distribution of loadl System integrity
You’ve seen them before; they are used in most applications tohelp them scale.MESSAGE QUEUE EXAMPLES
When to make use of message queues in case you’re wondering.GENERIC USE CASES
Overview of AMQPl AMQP Working Group (Community and Vendor)l Platform agnostic protocol.l Completely open, interoperable and broadly applicable.l Many severs available and many client libraries.
How it WorksProducer, Exchange, Queue, Consumer
How it Worksl AMQP utilizes exchanges, queues and bindings.l An exchange are routers with routing tables.l A binding defines the routing rules.l A queue is where the messages wait for a consumer.
Understanding Exchangesl Fanout Exchange l No routing keys involved. Any message that is sent to the exchange is sent to all queues bound to that exchange.l Direct Exchange l Routing keys involved. A queue binds to the exchange to request messages that match a routing key exactly.l Topic Exchange l Routing keys involved. A queue binds to the exchange to request messages that match a routing key pattern.
Implementations www.rabbitmq.com Very popular and common message queue owned by VMware. qpid.apache.org Long standing project; apache foundation. www.openamq.org Long standing project; ZeroMQ partner, no news since 2009.
Building a Queuel An exchange, queue and bindings must be defined first. Publishing can then commence after. l Create the queue l Create the exchange l Bind to the queue.
Persistence?l Default behavior is no persistence.l How important are the messages?l Just about all items have a level of persistence if you would like them to survive on reboot. l Mark exchanges, queues and messages as DURABLE.
STOMPSimple (or Streaming) Text Orientated Messaging Protocol
Overviewl Simple protocol l Behaviors follow very simple commands.l Most message queues can communicate over STOMP.
/queue/ msg Connect Send Disconnect /queue/ S msg T O Connect Subscribe Disconnect M P P H S P E R V Read E R AckHow It Worksl When you send in a message, you tell it which queue to go to.l When you subscribe you request a queue.
Sever Implementations activemq.apache.org One of the oldest message queues existing; a apache foundation project activemq.apache.org/apollo Next generation ActiveMQ www.rabbitmq.com Very popular and common message queue owned by VMware. www.jboss.org/hornetq Supported by Red Hat Middle Ware division, picking up steam.
PECL Stompl pecl install stompl That was easy J
XMPPExtensible Messaging and Presence Protocol(Although not really a “Message Queue”)
Overviewl Best for real-time data.l Leveraging pub/sub can turn it into more of a generic message system.l Multiple libraries l JAXL - https://github.com/abhinavsingh/JAXL l Xmpp - https://github.com/alexmace/Xmpp
Publish to, id, message Subscribe id, from, to, message Sub1 Sub2 Sub3XEP-0060: Publish-Subscribel Specification for implementing Publish Subscribe models.l Extension to the original XMPP specification.
Beanstalkdl Asynchronous Job Queuel Good scheduling system (aka delays).l User land PHP clients.
Application Code Beanstalkd Client API (Pheanstalk) Beanstalkd Server Beanstalkd Worker API (Pheanstalk) Worker Application CodeBeanstalkdl Pass a job to the job serverl Worker receives the job and processesl Ability to persist to binlog; default is in-memory
Messages• Formatting – JSON or XML are great options. • Please no serialized PHP objects.• Message Size – Only as large as necessary. • Don’t send a binary object through the queue.
Workers• Dumb as possible! – Single message type • Easier to scale. – Single operation • Easy to debug and far more flexible.
PHP Daemons• Prevent Memory Leaks – Detection – Cycle Workers• Handle Signals – Properly shutdown! – Watch out for OS service kills• Sleeping is good J
Database Worker Server Web Server Message QueueEnvironment IntegrationWeb Server -> Message QueueWorker Server -> Message Queue
Database Web Server Worker Server Worker Server Message Queue Send to 1 Message QueueHigh AvailabilityInsert multiple message queue servers + multiple worker nodes.Each worker node can connect to as many message queue serversas necessary.
SupervisordProcess monitoring, logging and more!