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Running a Scalable And Reliable Symfony2 Application in Cloud (Symfony Sweden November Camp 22 Nov 2013)


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Slides of my half an hour talk at Symfony Sweden November Camp, held at Hilton Slussen on Friday 22nd Nov 2013. Slides contain a generic infrastructure overview of running on Amazon Web Services and show a few details to consider when designing and running a distributed, reliable and scalable PHP application.

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Running a Scalable And Reliable Symfony2 Application in Cloud (Symfony Sweden November Camp 22 Nov 2013)

  1. 1. Running a scalable and reliable Symfony2 application 22nd Nov 2013 Symfony Sweden November Camp
  2. 2. @vjom = Ville Mattila | | • CTO & President of the board in Eventio Oy – We provide IT tools and services for event organizers – Office(s) in Kaarina & Turku (Åbo), Finland • Our flagship product runs on Symfony 2.3
  3. 3. Being a reliable means that you accept and prepare that ANYTHING CAN FAIL, ANY TIME (scalability comes free on top)
  4. 4. Our Infrastructure • • • Region: eu-west-1 Multiple AZ’s Auto-scaling Load Balancer (ELB) PHP/HTTP Servers (EC2) PHP/CLI Background Workers (EC2) (RDS Multi-AZ) CDN (CloudFront) S3 Storage for ”in-app” files S3 Storage for assets
  5. 5. Session Handling Store Sessions in Database • Replace NativeFileSessionHandler with an existing database handler or create your own config.yml: services: my.distributed.session_handler: class: MyDistributedSessionHandler arguments: [ . . . ] framework: session: handler_id: my.distributed.session_handle Symfony2 offers handlers for PDO, MongoDB and Memcached by default!
  6. 6. Session Handling Beware of Race Conditions • Default SessionHandler implementations (or PHP itself) do not implement any kind of locking • Only session snapshot from the request that finishes last is stored (other changes vanish) Request #1 $session->set(“email”, “”) Request #2 TIME $session->set(“twitter”, “vjom”); // // // // Some time consuming operation that takes seconds... like email validation. Request #3 // And other operations $session->set(“name”, “Ville”) exit; // And other operations exit; exit;
  7. 7. Session Handling in • Symfony2 (”browser”) sessions in Redis Cluster, without locking The ”business session” identifier Flash Messages Other temporary and/or cached data PredisSessionHandler is in our GitHub • ”Business sessions” are stored in MongoDB • Common identifier for the user’s or customer’s session throughout the system • Business sessions are never purged for accounting and auditing reasons • Updates to session parameters are done atomically (by Doctrine ODM)
  8. 8. Background Processing return new Response(); // ASAP!
  9. 9. Background Processing Flow Controller validates the request. On PHP/HTTP Servers POST /get_report {”poll”: ”/is_ready?handle=1234”} ReportController:: generateAction() The actual task is passed to the queue GET /is_ready?handle=1234 ReportController:: pollAction() {”status”: ”wait”} Queue Abstraction Library Status reports to a shared store. On PHP/CLI Worker Servers Task Processor QH invoked CLI Process Queue Handler (QH) Long running CLI Process … and forwards it to another process that does the actual job. Queue Implementation EventioBBQ is in our GitHub Queue Handler asks new jobs from the queue
  10. 10. Session Handling Reporting Status • Pattern 1: Send status reports to a database (or a key-value store) // Set status in a background worker $predis->set('bg_task_status:' . $handle, 'completed'); // Get status in the poll handling controller $predis->get('bg_task_status:' . $handle); • Pattern 2: Pass result to a (temporary) queue and poll the queue for status reports
  11. 11. Remember with CLI Workers • Service Container’s request scope is not available Use service_container and/or abstract away the requested feature. • Session information is not directly available in worker processes • We pass Session ID (and Request ID) with the job and recreate the environment for the background process • service_container is a great help here
  12. 12. S3 as a Common File Store • Send files to S3 with a simple HTTP Call • Files are accessible over HTTP by the application (private) or directly by external users (public) • URL signing enables you to grant temporary access also to private files • Object Expiration for a bucket works as a /tmp for cloud // composer.json "require": { "aws/aws-sdk-php": "2.*" } $objectParams = array( 'Bucket' => '...', 'Key' => 'my/files/pngfile.png', 'Body' => $fileContents, 'ACL' => CannedAcl::PRIVATE_ACCESS, ); $s3->putObject($objectParams); @see $objectParams = array( 'Bucket' => '...', 'Key' => 'my/files/pngfile.png', 'SaveAs' => '/run/shm/pngfile.png', ); $s3->getObject($objectParams);
  13. 13. Reliable Cron How to ensure that 1) a cron initiated process is run only once (to avoid double actions)? 2) cron processes are not our single point of failure?
  14. 14. Reliable Cron instance-1 instance-2 instance-3 eventio:cron is run at every instance, at every minute Every eventio:cron process tries to acquire a global lock, but only one gets it SETNX cron:lock:2013-11-22T11:30:00Z instance-1 From Redis documentation: SETNX Set key to hold string value if key does not exist. In that case, it is equal to SET. When key already holds a value, no operation is performed.
  15. 15. Reliable Cron CronBundle is in our GitHub instance-1 instance-2 instance-3 The current timestamp is persisted and used in future processing Instance that receives the lock continues the cron process and triggers cron.tick event in the application. $cronTime = new DateTime(date("Y-m-d H:i:00")); $cronEvent = new CronEvent($cronTime); $this->get('event_dispatcher')->dispatch('cron.tick', $cronEvent); Job classes listen for the triggered cron.tick event: Decide if we should do something now. Use $cronTime as the current time. class CronJob { public function run(CronEvent $event) { $cronTime = $event->getCronTime(); if ($cronTime->getTimestamp() % (5 * 60)) { return; } // Do the task but consider current time as $cronTime! } } Consider background workers.
  17. 17. Asset Deployment <commithash> Deploymen t master server Asset hash is stored in a simple <commithash>.txt file in our asset S3 bucket The master server creates a hash of all asset files and their (original) contents with the help of assetic:list If the asset S3 bucket does not have /<assethash>.txt file, deployment master does a full assetic:dump and uploads the dumped asset files to the S3 bucket under /<assethash>/ directory. This ensures that HTTP caches are busted.
  18. 18. Application deployments <commithash> Deploymen t master server • • • cache:clear Quick local & connectivity tests (Instance registration back to ELB) Instance is unregistered from the Load Balancer S3 bucket is queried for the <assethash> matching the current <commithash> … and added to the parameters.yml asset_hash: <assethash> config.yml: framework: templating: assets_base_urls: ["https://.../%asset_hash%"]
  19. 19. Thanks!