1) The document describes the evolution of an architecture from a "Spaghetti Architecture" to using Event Sourcing and CQRS. It outlines a maturity model with 6 levels: from Spaghetti to Hexagonal to adding Domain Events to using CQRS as a stepping stone to full Event Sourcing and CQRS. 2) As the architecture evolved through each level, it improved separation of concerns, testability, and addressed new issues like complexity and performance. Domain Events were added to help decompose tasks and sync events. CQRS was introduced to improve performance of read models. 3) Fully implementing Event Sourcing would involve entities being reconstituted from stored events rather than loaded from a

1. A Journey from
Hexagonal Architecture
to Event Sourcing
Carlos Buenosvinos (@buenosvinos)
SymfonyCon Cluj 2017, November 16th, 2017

2. Who am I?
Carlos Buenosvinos
• VP of Technology @ XING
• Consultant as a Hobby
• +10 years on Tech Leadership
(CTO, VP of Engineering, Director)
• Teams up to 100 people
• E-Commerce, E-Learning,
Payments, Classifieds, Recruiting
• Atrápalo (500M EUR),
PCComponentes (300M EUR)

3. @buenosvinos

4. Domain-Driven
Design in PHP Book
Carlos Buenosvinos, Christian Soronellas and Keyvan Akbary
https://leanpub.com/ddd-in-php

6. I want to tell
you a real story about…
6

7. a Company
evolving its architecture.
7

8. Buenosvinos
Maturity Model
8
Level 1: Spaghetti
Level 2: Framework Fanboy
Level 3: Hexagonal Architecture
Level 4: Hex. + Domain Events
Level 5: Stepping Stone (CQRS)
Level 6: Event Sourcing + CQRS

9. Spaghetti
Architecture
9
• Multiple Application Entry Points
- create_user.php, delete_user.php, …
• Infrastructure and Domain Together
- PHP and SQL within HTML
• Lack of Testing
• Difficult to Maintain

10. Framework Fanboy
Architecture
10
• Single Application Entry Point
- app.php
• Some structure is present (MVC)
• Still Mixing Infrastructure and Domain
- Long Controllers with SQL and
Business Logic, Dummy Entities
(getters and setters)
• No testing or using Web Framework
• Difficult to upgrade Infrastructure
Components

11. 11
Application
Service
Any Random
Action in a Web
Controller

12. Benefits of
Hexagonal Architecture
12
• Separation of Concerns
• Promotes decoupling from the
Framework
• Delays Infrastructure Decisions
- Persistence Storage or Delivery
Mechanism (Web, API, CLI, etc.)
• Easy to Test
- Testing Application Services (or CH)
- Testing Entities
- Mocking between the boundaries

13. 13
Web Controller

14. 14
Application
Service

15. Moving to
Hexagonal Architecture
15
1. Pick an action in the Web Controller
Identify Infrastructure references (ORM,
HTTP Rest Calls, Caching, etc.)
Extract Variable and move them to the top
2. Extract Business Logic into Application
Services (Extract Class/Copy & Paste)
3. Move Infrastructure references away
ORM flush() into add() in Repositories
4. Start Unit Testing from Application
Services

16. New Tech Policies in the Team:
1. Everything New: Hexagonal Architecture
2. Touching an Old Feature: Boy Scout Rule ("Always leave
the campground cleaner than you found it.”)
3. 100% Coverage in the Application Services
16

17. 17
Coverage
going up!

18. Buenosvinos
Maturity Model
18
Level 1: Spaghetti
Level 2: Framework Fanboy
Level 3: Hexagonal Architecture
Level 4: Hex. + Domain Events
Level 5: Stepping Stone (CQRS)
Level 6: Event Sourcing + CQRS

19. At this point,
you can be consultant too!
19

21. 21
“… and I want to
notify the user by
email, logging and
sending a BI tracking”
Company’s Product Owner

22. 22

23. Team starts to
face new issues
23
• # of Dependencies Grows
• Application Service complexity Grows
• More Chances to introduce Bugs
- More developers touching the same
file (Main Task and Subtasks mixed)
• More Subtasks in the same feature,
Worse Performance!!

24. Domain Events
to the rescue!
24

25. 25
Domain Event
Example

26. 26
Firing a Domain
Event

27. 27
Domain Event
Publisher
Example

28. 28
Domain Event
Listener
(Elastic Example)

29. 29

30. 30
Domain Event
Listener
(MySQL Example)

31. 31
Domain Event
Listener
(Rabbit Example)

32. 32
Registering
Domain Event
Listeners

33. Sync all the
things!
…and buy more servers
33

34. TechPoliciesAdded (ok, it’s a bad joke!)
1. Subtasks of a Feature are developed in a different
Application Service and attached via Listener
2. Fire any new Event that Business may be interested
3. Let’s have a TV screen to monitor realtime Business
metrics to be proactive.
34

35. 35
Composition by
Domain Events

36. Buenosvinos
Maturity Model
36
Level 1: Spaghetti
Level 2: Framework Fanboy
Level 3: Hexagonal Architecture
Level 4: Hex. + Domain Events
Level 5: Stepping Stone (CQRS)
Level 6: Event Sourcing + CQRS

37. 37
“Hey team! Have you
realised that the item
page is getting quite
slow?”
Company’s Product Owner

38. Perfomance!
Multiple Costly Requests
(#, external, joins, etc.)
38

39. Async all the
things!
39

40. CQRS
to the rescue!
40

41. 41

42. 42

45. Problem #1:
2 Infras / 1 Tx
45

46. What strategies to deal with these
inconsistencies can we follow?
46
• Let inconsistencies happen
- The Command Handler will manage
itself (firing ArticleWasAdded, sent to
RabbitMQ, but failed Database Tx)
- Feasible for most operational tasks
(sending email, non-critical tracking,
etc.)
• New Article Added Action and its Event
persisted in the same Tx. Then Worker
to move Events to Rabbit.
• Global TX (Noooooooooo!)

48. Problem #2:
Diff(ORM) !== Diff(Events)
48

50. Changes from Hexagonal Architecture
to Stepping Stone (CQRS)
50
• Entity state is still fetched from the
database (read)
- 3rd Normal Form
- Now database is a cache
• Entities hold events triggered
- Use a trait or a base class
• Repositories now only persist a bunch
of events to your queue (no updates)
- You will only send messages to
RabbitMQ or your queue

51. 51
Max
Performance!

53. Buenosvinos
Maturity Model
53
Level 1: Spaghetti
Level 2: Framework Fanboy
Level 3: Hexagonal Architecture
Level 4: Hex. + Domain Events
Level 5: Stepping Stone (CQRS)
Level 6: Event Sourcing + CQRS

54. I want it all!
54

55. What’s remaining to
get to Event Sourcing?
55
• Entities state is not loaded from the
database, is reconstituted from the
Events from the Event Store.
• Migrate Entities one at a time.
• Enjoy!

56. Buenosvinos
Maturity Model
56
Level 1: Spaghetti
Level 2: Framework Fanboy
Level 3: Hexagonal Architecture
Level 4: Hex. + Domain Events
Level 5: Stepping Stone (CQRS)
Level 6: Event Sourcing + CQRS

57. Thank you
for your attention.
https://joind.in/talk/21555
@buenosvinos