Hexagonal architecture message-oriented software design
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Commands, events, queries - three types of messages that travel through your application. Some originate from the web, some from the command-line. Your application sends some of them to a database, or a message queue. What is the ideal infrastructure for an application to support this on-going stream of messages? What kind of architectural design fits best? This talk provides answers to these questions: we take the *hexagonal* approach to software architecture. We look at messages, how they cross boundaries and how you can make steady communication lines between your application and other systems, like web browsers, terminals, databases and message queues. You will learn how to separate the technical aspects of these connections from the core behavior of your application by implementing design patterns like the *command bus*, and design principles like *dependency inversion*.
![Low-level API
$requestContent = file_get_contents('php://input');
$contentType = $_SERVER['CONTENT_TYPE'];
if ($contentType === 'application/json') {
$data = json_decode($requestContent, true);
} elseif ($contentType === 'application/xml') {
$xml = simplexml_load_string($requestContent);
...
}](https://image.slidesharecdn.com/hexagonalarchitecture-message-orientedsoftwaredesign-150918150231-lva1-app6891/85/Hexagonal-architecture-message-oriented-software-design-12-320.jpg)
!["A good software architecture allows decisions [...]
to be deferred and delayed."
–Robert Martin, Screaming Architecture](https://image.slidesharecdn.com/hexagonalarchitecture-message-orientedsoftwaredesign-150918150231-lva1-app6891/85/Hexagonal-architecture-message-oriented-software-design-70-320.jpg)
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Hexagonal architecture message-oriented software design
- 1. HEXAGONAL ARCHITECTURE Message oriented software design By Matthias Noback
- 5. Your brain can't handle it M V C ?
- 6. Coupling to frameworks and libraries ! ! !
- 7. How do you start a new project? Pick a framework Install a skeleton project Remove demo stuff Auto-generate entities Auto-generate CRUD controllers Done "It's a Symfony project!"
- 8. That's actually outside in The boring stuff The interesting stuff Symfony Doctrine RabbitMQ Redis Angular
- 10. Why do frameworks not solve this for us? Because they can't ;)
- 12. Low-level API $requestContent = file_get_contents('php://input'); $contentType = $_SERVER['CONTENT_TYPE']; if ($contentType === 'application/json') { $data = json_decode($requestContent, true); } elseif ($contentType === 'application/xml') { $xml = simplexml_load_string($requestContent); ... }
- 13. Nicely hides the details $data = $serializer->deserialize( $request->getContent(), $request->getContentType() );
- 14. Low-level API $stmt = $db->prepare( 'SELECT * FROM Patient p WHERE p.anonymous = ?' ); $stmt->bindValue(1, true); $stmt->execute(); $result = $stmt->fetch(PDO::FETCH_ASSOC); $patient = Patient::reconstituteFromArray($result);
- 15. Hides a lot of details $patient = $repository->createQueryBuilder('p') ->where('p.anonymous = true') ->getQuery() ->getResult();
- 17. $patient = $repository->createQueryBuilder('p') ->where('p.anonymous = true') ->getQuery() ->getResult(); Concrete Concrete Concrete
- 19. Coupling to the delivery mechanism
- 20. public function registerPatientAction(Request $request) { $patient = new Patient(); ! $form = $this->createForm(new RegisterPatientForm(), $patient); ! $form->handleRequest($request); ! if ($form->isValid()) { $em = $this->getDoctrine()->getManager(); $em->persist($patient); $em->flush(); ! return $this->redirect($this->generateUrl('patient_list')); } ! return array( 'form' => $form->createView() ); } Request and Form are web-specific EntityManager is ORM, i.e. relational DB-specific
- 24. Lack of intention-revealing code
- 25. data data data
- 26. public function updateAction(Request $request) { $patient = new Patient(); ! $form = $this->createForm(new PatientType(), $patient); ! $form->handleRequest($request); ! if ($form->isValid()) { $em = $this->getDoctrine()->getManager(); $em->persist($patient); $em->flush(); ! return $this->redirect($this->generateUrl('patient_list')); } ! return array( 'form' => $form->createView() ); } from the HTTP request copied into an entity then stored in the database What exactly changed?! And... why?
- 27. R.A.D. Rapid Application Development B.A.D. B.A.D. Application Development
- 28. In summary Coupling to a framework Coupling to a delivery mechanism (e.g. the web) Slow tests Lack of intention in the code
- 29. THE ESSENCE of your application
- 31. The "heart"?
- 32. "The heart of software is its ability to solve domain-related problems for its users. –Eric Evans, Domain Driven Design All other features, vital though they may be, support this basic purpose."
- 33. What's essential? Domain model Interaction with it Use cases
- 35. “The database is an implementation detail” –Cool software architect
- 36. The core doesn't need to know about it ! ! !
- 38. The core doesn't need to know about it ! ! !
- 39. Infrastructure The world outside ! ! ! Web browser Terminal Database Messaging Filesystem (E)mail
- 40. Mmm... layers Layers allow you to separate Layers allow you to allocate Layers have boundaries Rules for crossing
- 41. Rules about communication Actually: rules about dependencies
- 42. The dependency rule –Robert Martin, Screaming Architecture
- 44. Messages someFunctionCall( $arguments, $prepared, $for, $the, $receiver ); $message = new TypeOfMessage( $some, $relevant, $arguments ); handle($message);
- 45. What about the application boundary? The app Message The world outside
- 46. How does an app allow incoming messages at all? By exposing input ports Routes Console commands A WSDL file for a SOAP API
- 49. Ports use protocols for communication Each port has a language of its own
- 50. Web (HTTP)
- 51. Messaging (AMQP)
- 52. HTTP Request Form Request Controller Entity Value object W eb port Translate the request Repository
- 53. Adapters The translators are called: adapters
- 54. "Ports and adapters" Ports: allow for communication to happen Adapters: translate messages from the world outside == Hexagonal architecture Alistair Cockburn
- 55. An example Plain HTTP message $_POST, $_GET, $_SERVER, Request POST /patients/ HTTP/1.1 Host: hospital.com ! name=Matthias&email=matthiasn [email protected] Command $command = new RegisterPatient( $request->get('name'), $request->get('email') );
- 56. Command $command = new RegisterPatient( $request->get('name'), $request->get('email') ); Expresses intention Implies change Independent of delivery mechanism Only the message
- 57. class RegisterPatientHandler { public function handle(RegisterPatient $command) { $patient = Patient::register( $command->name(), $command->email() ); $this->patientRepository->add($patient); } } Command Command handler
- 60. Change New entity (Patient) Entity- Manager UnitOf- Work $patient = Patient::register( $command->name(), $command->email() ); $this->patientRepository ->add($patient); Insert query (SQL) INSERT INTO patients SET name='Matthias', email='matthiasnoback@gmai l.com';
- 64. What often goes wrong: we violate boundary rules...
- 67. PatientRepository (uses MySQL) Domain Infrastructure Application Domain RegisterPatient- Handler
- 70. "A good software architecture allows decisions [...] to be deferred and delayed." –Robert Martin, Screaming Architecture
- 71. IN CONCLUSION what did we get from all of this?
- 75. This is all very much supportive of... See also: Modelling by Example DDD TDD BDD CQRS