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Working with Asynchronous Events
The document discusses techniques for processing asynchronous events in PHP using Symfony and RabbitMQ, including the need for asynchronous processing to improve reaction times and manage load. It highlights tools like Gearman and Resque, and covers lessons learned regarding message management, transformation, and consumer handling in RabbitMQ. Key considerations include managing message format, unique identifiers, and the potential for toxic messages resulting from improper handling.
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Working with Asynchronous Events
- 1. Working with Asynchronous Events JanGregor Emge-Triebel (@jan0707) Dennis Oehme (@dennisoehme)
- 2. Garden of ConceptsGmbH ● Hanau / Munich ● In house CMS “.stone” ● In house CRM “Elvis” ● Various individual customer projects ● Symfony based development, supported by: ○ MongoDB, ElasticSearch, MySQL, RabbitMQ, Redis, AngularJS, Twig, Jade, Gitlab, Docker, Vagrant, Ansible ● Say hi @goc_mediastudio
- 3. Requests == Event “Symfonyis a request based framework.” Fabien Potencier, Symfony Live 2014 @fabpot
- 4. Requests Request Controller Logic1 Logic 2 Response Request Controller Logic 1 Logic 2 Response Synchronous Asynchronous
- 5. Why do weneed asynchronous event processing ? ● Move long running logic ● Cut down reaction times ● Transfer load ● Microservices ● Exchange data/messages with other (sub-)systems ● Parallelization ● Scaling
- 6. Our journey ● Gearman ●(PHP) Resque ○ Demo ● RabbitMQ
- 7. Gearman ● Gearman JobServer (written in C) ● Runs as a Linux daemon ● Requires PECL extension for worker API ● Worker APIs exists for other Languages (C, Perl,...)
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- 9. Gearman ● Latest PECL-Extensionversion is 1.1.2 (August 2013) ● Latest Server-Release (spring 2014) ● No more process is being made ● Gearman daemon and extension are often incompatible
- 10. (PHP) Resque ● Isa Resque port to php: ○ Resque is a Redis-backed Ruby library for creating background jobs, placing them on multiple queues, and processing them later. ● Needs Redis(-Cluster) ● Redis is capable of atomic transactions (FIFO)
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- 12. (PHP) Resque ● Hardlyany commits since 2012 ● Last commit to Master on 2015-05-12 ● chrisboulton/php-resque & michelsalib/BCCResqueBundle must be presumed dead ?
- 13. RabbitMQ Or why thistalk should be named: “Working with Asynchronous Events in RabbitMQ”
- 14. RabbitMQ ● Message Brokerwritten in Erlang ● AMQP (Advanced Message Queuing Protocol) ● Open, but binary network protocoll ● Routing, message distribution ● Transactions ● Plus, more nice features ○ TTL ○ DLX (Dead Letter eXchange) ○ PreFetching
- 15. Of publishers andconsumers ... Publisher Publish Consumer Ex- change QueueRoutes Consumes
- 16. There is aBundle for it ● https://github.com/php-amqplib/RabbitMqBundle ● Consumer and Producer as Symfony services ● Every queue Consumer runs as a Symfony command ● Configuration via app/config.yml ○ Better: Create app/config/rabbitmq.yml and import in app/config/config.yml
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- 20. Lessons Learned: Consumer ●PHP threads are not meant to be long running ○ New problems: memory leaks, ... ● Use supervisor to check and restart Consumers ● Open database connections, timeouts ○ Better quit when inactive ● Cap maximum runtime per thread ○ Automatically shutdown after processign x messages ● Memory limit: RabbitMQ-Bundle utilizes “soft-quota” ● Booting consumers takes rather long ● Prefetching (Warning: Order!)
- 21. Lessons Learned: Message ●Compact/short messages ● Queues eat up a lot of storage / RAM ● Common format such as JSON or XML ○ Do not serialize PHP objects or arrays ○ Ensure interoperability with other systems and languages
- 22. Lessons Learned: MessageTransformation ● Use JMS/Serializer to convert objects to JSON ○ Deserialize JSON to PHP objects in consumer ○ Objects can and should be validated (with symfony forms and asserts) ○ Reload entities / documents to keep them up to date (doctrine/unit of work) ● Alternative approach: PHPs JsonSerializable Interface
- 23. Lessons Learned: MessageHeader ● Use message “Header” for content-type and version ○ Message formats can change ○ consumers must remain compatible ● Unqiue IDs make logging / debugging / live easier ● Other meta data: ○ timestamp ○ user / session ○ App id ○ ...
- 24. Tip: Custom Consumer-/Producer-Classes ●Message transformation ● Events ● Logging
- 25. Transactions ● Messages mustbe brokered to exactly one Consumer ● Consumer must explicitly answer a message with “acknowledge” ● If not, the message will be marked “rejected” and be requeued ○ Beware of requeuing: ■ Can lead to toxic messages ■ Can change the order of messages ○ Beware of final rejection: ■ Can lead to loss of data
- 26. Toxic Messages ● Ifa message is not explicitly being answered, it will be requeued. ● If that happens multiple times : ● Congratulations on your infinite loop ● Congratulations on your infinite loop ● Congratulations on your infinite loop ● Congratulations on your infinite loop ● Congratulations on your infinite loop ● Congratulations on your infinite loop ● Congratulations on your infinite loop
- 27. Dead Letter Exchange ●RabbitMQ comes with a Dead Letter Exchange (DLX) ● Every queue determines its own or shared DLX ● DLX is a separate queue, storing all rejected messages ○ (Reject, TTL, Prefetch)
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- 29. Signal Handling ● GracefulShutdown ● pcntl_signal / _dispatch ● SIGTERM ● FATAL ERROR abfangen ● Logging ● Toxic Message-Handling Shutdown
- 30. Deployment ● Consumers needan up to date code base ● Consumers need a graceful shutdown ● Consumers must only be shutdown when idling ○ Otherwise : Loss of message / data
- 31. Other challenges ● Significantchange of infrastructure ○ Choose your libraries and dependencies carefully! ● Moving load is not removing load ● Rethinking necessary ○ Display of status / intermediate result ○ Websockets or Push instead of Polling ● Interdependencies of messages ○ Especially when running parallel consumers! ● Performance (Doctrine ORM / ODM)
- 32. Questions ? Thank you:) Find this and other talks at: https://www.gardenofconcepts. com/talks/ Feedback is always welcome & please rate our talk !