Flipping out with Feature Flags & Toggles Symfony Live London 2016

Quite often it can be useful to enable new functionality for only certain users on your site, or perhaps to only enable it on a test version of your application. One method of doing this, with a single shared codebase, is feature flags, and is the method used by huge organisations with monolithic repositories like Flickr, but can also be used on much smaller scales when you want to test out new functionality in production or perform A/B testing.

This talk will guide you through why feature flags can be helpful to your development workflow, and how you can use them whilst avoiding too much added complexity to your application.

Transcript

1. FLIPPING OUT WITH FEATURE FLAGS & TOGGLES SYMFONY LIVE LONDON 2016 @MICHAELCULLUMUK
2. ME?
3. MICHAEL CULLUM @MICHAELCULLUMUK
5. BACK TO BASICS
6. CONDITIONALS <?php if (true) { oneAction(); } else { alternativeAction(); }
7. CONDITIONALS <?php if ($enabled) { oneAction(); } else { alternativeAction(); }
8. FEATURE FLAG <?php if (featureEnabled('twitter_seen')) { oneAction(); } else { alternativeAction(); }
9. WHAT’S IN A NAME?
10. SWIFT MAILER
11. SWIFT MAILER swiftmailer: disable_delivery: ~
12. SWIFT MAILER <?php if (isset($mailer[‘disable_delivery'])) { $transport = 'null'; $container->setParameter('swiftmailer.enabled', false); } else { $container->setParameter('swiftmailer.enabled', true); }
13. SWIFT MAILER <?php if (isset($mailer[‘disable_delivery'])) { $transport = 'null'; $container->setParameter('swiftmailer.enabled', false); } else { $container->setParameter('swiftmailer.enabled', true); }
14. STRUCTURING
15. SPLIT IT OUT <?php interface FeatureFlags { function isEnabled(string $flag): boolean }
16. HARDCODED <?php function isEnabled(string $flag): boolean { if ($flag == 'profile') { return true; } return false; } if (isEnabled('profile')) { newProfileMagic(); }
17. HARDCODED <?php function isEnabled(string $flag): boolean { if ($flag == 'profile') { return true; } return false; } if (isEnabled('profile')) { newProfileMagic(); }
18. PARAMETERS IN CONFIG FILES <?php function isEnabled(string $flag): boolean { if ($flag == 'mailDelivery') { return $this->container->getParameter('swiftmailer.enabled', $flag); } elseif (isset($this->container->getParameter(sprintf('flag.%s', $flag)))) { return $this->container->getParameter(sprintf('flag.%s', $flag)); } return false; }
19. CACHE function isEnabled(string $flag): boolean { $cache = $this->cache; $flag = $cache->getItem(sprintf('flag.%s', $flag)); if (!$flag->isHit()) { $flag->get(); } return false; }
20. DATABASE
21. VARY BY: ENVIRONMENT USER
22. ALTERNATIVE TO BRANCHING?
23. DIFFERENT SUBSET OF USERS
24. A/B TESTING
25. TEST IN PRODUCTION
26. MONOLITHIC REPOSITORIES
27. TEST A MATRIX OF CHANGES
28. MANAGING YOUR FLAGS
29. DATABASE
30. CODEBASE
31. USING THEM CLEANLY
32. TWIG {% if isFeatureEnabled('showCfpForm') %} {{ form(form) }} {% endif %}
33. TWIG <?php namespace AppBundle\Twig; class AppExtension extends \Twig_Extension { public function getFunctions() { return array( new \Twig_SimpleFunction('isEnabled', array($this, 'isEnabled')), ); } //.. }
34. COMPLEXITY <?php if ($container->getParameter('profileFeature')) { if ($container->getParameter('newProfileStyle')) { if ($container->getParameter('newProfileStyleButtons')) { enableButtons(); } if ($container->getParameter('myNewCoolProfilePic')) { renderPicture(); if ($container->getParameter('newProfileRenderEngine')) { tryDifferentRenderEngine(); } } renderNewProfiler(); } else { // Render the legacy profile } }
35. COMPLEXITY <?php if ($container->getParameter('profileFeature')) { if ($container->getParameter('newProfileStyle')) { if ($container->getParameter('newProfileStyleButtons')) { enableButtons(); } if ($container->getParameter('myNewCoolProfilePic')) { renderPicture(); if ($container->getParameter('newProfileRenderEngine')) { tryDifferentRenderEngine(); } } renderNewProfiler(); } else { // Render the legacy profile } }
36. COMPLEXITY <?php if ($container->getParameter('profileFeature')) { if ($container->getParameter('newProfileStyle')) { if ($container->getParameter('newProfileStyleButtons')) { enableButtons(); } if ($container->getParameter('myNewCoolProfilePic')) { renderPicture(); if ($container->getParameter('newProfileRenderEngine')) { tryDifferentRenderEngine(); } } renderNewProfiler(); } else { // Render the legacy profile } }
37. CONTROLLERS
38. CONTROLLERS - YAML profile: path: /profile/{user} defaults: _controller: DemoBundle:Profile:legacy _alt: DemoBundle:Default:new _flag: newProfile
39. CONTROLLERS - EVENT <?php public function onKernelRequest($event) { $flag = $event->getRequest->attributes->get('_flag'); $alternate = $event->getRequest->attributes->get('_alt'); if (isEnabled($flag)) { $event->getRequest->attributes->set(‘controller’, $alternate); } }
40. CONTROLLERS - EVENT <?php public function onKernelRequest($event) { $flag = $event->getRequest->attributes->get(‘_flag'); $alternate = $event->getRequest->attributes->get(‘_alt'); if (isEnabled($flag)) { $event->getRequest->attributes->set(‘_controller’, $alternate); } if (!isset($alternate) && isset($flag) && !isEnabled($flag)) { throw new NotFoundHttpException(); } }
41. CONTROLLERS - EVENT <?php public function onKernelRequest($event) { $flag = $event->getRequest->attributes->get(‘_flag'); $alternate = $event->getRequest->attributes->get(‘_alt'); if (isEnabled($flag)) { $event->getRequest->attributes->set(‘_controller’, $alternate); } if (!isset($alternate) && isset($flag) && !isEnabled($flag)) { throw new NotFoundHttpException(); } }
42. SERVICE FACTORIES
43. NON-GENERIC FACTORY <?php class ProfileFactory { public function create(): ProfileInterface { return isEnabled(‘newProfile’) ? $container->get(‘newProfile’) : $container->get(‘legacyProfile’); } }
44. GENERIC FLAGS FACTORY <?php class FlagsFactory { public function createService(string $flag, $service, $alternate) { return isEnabled($flag) ? $container->get($service) : $container->get($alternate); } }
45. GENERIC FLAGS FACTORY services: app.flagsFactory: class: AppBundle\FlagsFactory app.profileManager: class: AppBundle\Profile\ProfileManager factory: ['@app.flagsFactory', createService] arguments: - newProfile - legacyProfileManager - newProfileManager
46. ALLOWS YOU TO
47. BRANCHING WITHOUT CONFLICTS OR VCS
48. TEST IN PRODUCTION
49. SLOW ROLLOUT
50. FUNCTIONALITY ON DIFFERENT ENVIRONMENTS
51. A/B TESTING
52. CLEANLY
53. DATABASE OR CONFIGURATION FILES
54. AVOIDING LARGE CONDITIONALS
55. THANKS @MICHAELCULLUMUK
56. FLIPPING OUT WITH FEATURE FLAGS & TOGGLES SYMFONY LIVE LONDON 2016 @MICHAELCULLUMUK