Tips and Tricks for evolving your Architecture from Spaghetti to Event Sourcing.

1. A Journey from
Hexagonal Architecture
to Event Sourcing
Carlos Buenosvinos (@buenosvinos)
Polycon, October 6th, 2017
Barcelona

2. 2
Who am I?
Carlos Buenosvinos
• Technical Director @ XING
• Consultant
• +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
3

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

5. I want to tell
you a real story about…
5

6. a Company
evolving its architecture.
6

7. Spaghetti
Architecture
7
• 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

8. Framework Fanboy
Architecture
8
• 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

9. 9
Application
Service
Any Random
Action in a Web
Controller

10. I receive
an email
10

11. Buenosvinos
Maturity Model
11
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
* Tested with just 20 companies aprox.

12. Buenosvinos
Maturity Model
12
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
* Tested with just 20 companies aprox.

13. Benefits of
Hexagonal Architecture
13
• Separation of Concerns
• Decoupled 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

14. 14
Web Controller

15. 15
Application
Service

16. Moving to
Hexagonal Architecture
16
• Pick an action in the Web Controller
- Identify Infrastructure references
(ORM, HTTP Rest Calls, Caching, etc.)
- Extract Variable and to the top
• Extract Business Logic into Application
Services (Copy and Paste)
• Move Infrastructure references away
- ORM flush() into Repositories
• Start Unit Testing from Application
Services

17. 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
17

18. 18
Coverage
going up!

19. Buenosvinos
Maturity Model
19
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
* Tested with just 20 companies aprox.

20. At this point,
you can be consultant too!
20

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!
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
* Tested with just 20 companies aprox.

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

41. Have you ever sent an
email about something
that didn’t finally
happen?
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!)

47. Problem #2:
Diff(ORM) !== Diff(Events)
47

49. 49
Max
Performance!

50. Buenosvinos
Maturity Model
50
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
* Tested with just 20 companies aprox.

52. Buenosvinos
Maturity Model
52
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
* Tested with just 20 companies aprox.

53. What should be next?
Getting Ready for Event Sourcing
53
• Entities are loaded from the Events
already Stored
• Our Main Database is nothing but a
Cache (Can we get rid of it? How much
does it cost?)
• Watch Marco Pivetta’s Presentation
and/or attend his Workshop on Sunday.

54. Thank you
for your attention.