From CRUD to Hexagonal & DDD, how Meetic saved its codebase

Frameworks give us a CRUD mindset, not suited to handle business complexity.
Discover patterns you can re-use on your project, that really helped us, and tips to spread a new culture amongst your colleagues.
Hosted by Polymorphic meetup group : https://www.meetup.com/fr-FR/Polymorphic/events/260342370/

Transcript

1. From CRUD to Hexagonal & DDD “How Meetic saved its codebase” Icons made by Icongeek26, Freepik from www.flaticon.com Jean-Marie Lamodière - Backend tech lead @jmlamodiere
2. stackshare.io/meetic @meetictech microservice calls Kafka messages production deployments 3 500 000 000 250 000 000 25 / day
3. Legacy REST API Buzzwords Evangelism 2002-2012 2013 2015-2018 2018
4. WHY ? n-tiers architecture Presentation (Apps) Presentation Business logic Data access
5. But… Monolithic Rest API = new Legacy v2 Icons made by Freepik from www.flaticon.com
6. What’s wrong ? We use a modern web framework ! We follow its best practices ! Icons made by Freepik from www.flaticon.com
7. WHY ? MVC Framework = CRUD Create Read Update Delete = Database mindset Icons made by Smashicon from www.flaticon.com
8. WHY ? MVC Framework = CRUD Typical tutorial : 1. Generate entities + getters + setters 2. Generate Database 3. Expose as REST (or web <form>)
9. WHY ? MVC Framework = CRUD N-tiers architecture Presentation Business logic Data access Framework focus Framework focus ...YOLO ! Icons made by Freepik, Smashicon from www.flaticon.com
10. WHY ? Tests… with code coverage in mind Complex Class Icons made by Pause08, Freepik from www.flaticon.com = No refactoring Test coupled with internal details + 100%
11. What is a useful test ? How to code business complexity ? Icons made by Freepik from www.flaticon.com
12. Legacy REST API Buzzwords Evangelism 2002-2012 2013 2015-2018 2018
13. WHY ? Let’s try buzzwords ! Test Driven Development Behaviour Driven Development Command Bus Hexagonal architecture Domain Driven Design Command Query Separation Icons made by Roundicons from www.flaticon.com Microservices
14. WHY ? 3 years later... • Inconsistant code designs • Differing opinions amongst developers Fewer libraries! More libraries! Get sh*t done! Refactor everything! Fewer libraries! More libraries! Refactor everything!
15. Legacy REST API Buzzwords Evangelism 2002-2012 2013 2015-2018 2018
16. WHY ? Evangelism Pro-tips • Lead by example Pull Requests, Pair Programming • Organize debates Teach, show code, vote • Code example as documentation • Use (anti-)pattern names
17. Hexagonal Architecture = Ports & Adapters Dr. Alistair Cockburn - 2005 Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips
18. WHY ?What is “Decoupling” ? Low coupling High cohesion “Allow unrelated things to change independently” Icons made by Roundicons from www.flaticon.com
19. WHY ?Hexagonal architecture Low coupling High cohesion “Decoupling business and technical choices” Icons made by Roundicons from www.flaticon.com
20. WHY ?Hexagonal architecture “Techno agnostic domain” Infrastructure • Framework (+ version) • Libraries (ORM, http client) • Database • REST, SOAP, Command line ? Domain (Business logic)
21. WHY ? Where to put my code ? Infrastructure Framework, libraries, techno Domain (Business logic) Icons made by Icongeek26 from www.flaticon.com Product Owner Business expert Architect Dev, Ops (Who decides ?)
22. WHY ?Domain inside hexagon RepositoryInterface Entity No framework Icons made by Freepik from www.flaticon.com /Domain MemberRepository Member Screaming architecture
23. WHY ? Port = simplest interface meeting use-case needs UseCase RepositoryInterface Entity Start inside hexagone, free your mind from infrastructure No framework Icons made by Freepik from www.flaticon.com
24. WHY ? Port = simplest interface meeting use-case needs Icons made by Roundicons, Freepik from www.flaticon.com repo.persist(member).flush (framework details) repo.add(member) repo.get(id) A repository can be seen as a list
25. WHY ? Port = simplest interface meeting use-case needs Icons made by Roundicons, Freepik from www.flaticon.com Intention revealing interface getInactiveMembers() getDefaultChoices(gender) increaseCounter()
26. WHY ? Adapter = techno-specific “driver” UseCase RepositoryInterface Entity MysqlRepository HttpRepository No framework Framework welcome Icons made by Freepik from www.flaticon.com TestRepository
27. WHY ? Adapter = techno-specific “driver” MysqlRepository Icons made by Freepik from www.flaticon.com /Domain MemberRepository Member /Infrastructure MysqlMemberRepo... Framework welcome
28. WHY ? MysqlMemberRepository implements MemberRepositoryInterface { getInactiveMembers() {...} } Adapter = techno-specific “driver” Techno name Icons made by Freepik from www.flaticon.com
29. WHY ? Adapter = techno-specific “driver” UseCase RepositoryInterface Entity MysqlRepository @Throws UserNotFound Icons made by Freepik from www.flaticon.com Convert infra exceptions to domain exceptions
30. WHY ? Adapter = techno-specific “driver” UseCase RepositoryInterface Entity AggregatorRepository MysqlDao* CacheDecoratorDao HttpDao *Data Access Object (No impact here) Icons made by Freepik from www.flaticon.com (Complex infra)
31. WHY ? Difference with n-tiers architecture Service MysqlDao1* Dto1* Dao2Interface *Data Access Object *Data Transfert Object CacheDecoratorDao2 HttpDao2 Dto2 (Aware of 2 Dao) (Mimic database structure)
32. WHY ? Port & Adapters : entrypoints UseCase RepositoryInterface Entity RestController Test CliController No framework Framework welcome Icons made by Freepik from www.flaticon.com
33. RestController Framework welcome Icons made by Freepik from www.flaticon.com /Infrastructure /Symfony MemberController MemberSerializer WHY ? Port & Adapters : entrypoints
34. WHY ? Ex. of adapter refacto @Meetic Symfony 2 Database Database Oracle Icons made by Freepik from www.flaticon.com Symfony 4 External REST API Config files PostgreSQL
35. WHY ?Layers inside hexagone UseCase RepositoryInterface Entity Icons made by Freepik from www.flaticon.com Application Use cases (do, get…) Domain Modeling business reality (Use case agnostic)
36. Command Query Separation Command (do) : produces an effect Query (get) : gets data, no state change Same as “Query” vs. “Mutation” in GraphQL Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips
37. WHY ? Command / Query Separation RepositoryInterface Entity Icons made by Freepik, Smashicons from www.flaticon.com Query Handler Command Handler
38. WHY ? Command / Query Separation /Application /Command RegisterMember RegisterMemberHandler /Query GetNewMembers GetNewMembersHandler /Domain MemberRepository Member
39. WHY ? Command / Query Separation Command, Query • simple DTO • user intention • primitive values /Application /Command RegisterMember RegisterMemberHandler /Query GetNewMembers GetNewMembersHandler
40. WHY ? Steps 1. Infrastructure\Controller Converts HTTP request to Command/Query and call Handler 2. Application\CommandHandler Apply logic, act on Entity through Repository 3. Infrastructure\Controller Send HTTP response
41. WHY ? Command / Query Separation Command Handler RepositoryInterface Entity Icons made by Freepik, Smashicons from www.flaticon.com Query Handler DaoInterface DTO (with validation) (no logic, readonly) Same database (≠ CQRS)
42. WHY ? Command / Query Separation /Application /Command RegisterMember RegisterMemberHandler /Query GetContactPictures GetContactPicturesHandler /Domain MemberRepository Member /Read ContactDao ContactPicture
43. WHY ? Command / Query Separation Create custom Read DAO only when it simplifies code Ex : custom DTO with less fields
44. Domain Driven Design Eric Evans - 2004 Icons made by Icongeek26, Freepik from www.flaticon.com Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips
45. WHY ? Domain Driven Design • Talk with domain experts • Use domain words in your code • Focus on events instead of data Icons made by Icongeek26 from www.flaticon.com
46. WHY ? Domain Driven Design Make domain logic explicit
47. WHY ? Before DDD : fake entities... Anemic domain model Temporal coupling memberEntity .setStatus(“active”) .setActivationDate(now) .setCanTalk(true) Icons made by Roundicons from www.flaticon.com Feature envy
48. WHY ? Same (anti)patterns with REST PUT /member/123 {“status”: “active”, “activDate”:”now”“canTalk”:true} Icons made by Roundicons, Freepik from www.flaticon.com POST /member/123 {“action”: “activate”} Logic on caller = feature envy POST /member/123/activate
49. WHY ? DDD Entity Rich domain model Icons made by Roundicons from www.flaticon.com memberEntity .activate() • State always valid (check invariants) • Explicit mutators • Emit domain events
50. WHY ? Before DDD : primitive types only... Icons made by Roundicons from www.flaticon.com Primitive obsession productEntity .setPriceAmount(20.50) .setCurrenty(“EUR”) (same concern)
51. WHY ? DDD Value Object price = new Price(20.50, “EUR”) productEntity .setPrice(price) • Explicit • Immutable • Valid
52. WHY ? DDD Value Object @ Meetic age = new Age(23) … = age .toSearchBirthdayMax() • Factorize validation • Factorize features Must be >= 18
53. Testing strategy Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips Icons made by Freepik from www.flaticon.com
54. WHY ? Inside hexagon: unit tests Command Handler RepositoryInterface Entity Icons made by Freepik, Smashicons from www.flaticon.com • Mock Infra only • Don’t mock entities / value objects Test Mock
55. WHY ? Outside hexagon: integration tests Icons made by Freepik, Smashicons from www.flaticon.com Don’t mock a library API The test should allow refactoring : • QueryBuilder -> SQL • Change Http library MysqlRepository Docker mysql HttpRepository Wiremock
56. Gotchas ? Pro-Tips ? Hexagonal Architecture Command / Query Separation Domain Driven Design Testing Strategy Gotchas Pro-Tips Icons made by Freepik from www.flaticon.com
57. WHY ? Do not stack new layers Lava flow Refacto “vertical” business slices Icons made by Freepik, Pixel Perfect, Roundicons from www.flaticon.com New layer Old layer 1 Old layer 2
58. WHY ? Gotchas, Pro-tips • Hexagon overkill when no domain logic. CRUD / framework magic more suited. • Start inside hexagon, not with database. Otherwise, infra complexity will leak into domain • To choose layer => whose decision is it ? Product Owner Business expert Architect Dev, Ops @jmlamodiere Icons made by Icongeek26 from www.flaticon.com Thanks for coming !