Le projet Legacy : quelles stratégies pour s'en sortir ? — ATBDX 2020

Transcript

1. None

2. What is Legacy Code ? Definition

3. A code you want to change that no one understands

   but still provides value. Definition

4. A code without predictability Definition

5. A code without predictability Definition Developers have no idea how

   long a change can take 01. 02. There is no correlation between the business and the technical complexity 03. You don’t know when something will break

6. A code with no test Definition

7. A code with no test Definition « Most of the

   fear involved in making changes to large code bases is fear of introducing subtle bugs; fear of changing things inadvertently. Without test, you just don’t know whether things are getting better or worse. » — Michael Feathers

8. An inverse problem Definition

9. An inverse problem Definition Observations Causes Forward problem Inverse problem

10. An inverse problem Definition

11. Hello, I am a software developer. My name is Arnaud

    LEMAIRE, and you can find me on lilobase.me & @lilobase Who am I?

12. This talk is focused on strategic considerations and not tactical

    ones Disclaimer

13. A natural process Why does it appear?

14. A natural process Why does it appear? Add lines of

    code More complexity Increase in software entropy Legacy Code

15. You need to let your software die* A natural process

    that cannot be stopped

16. You need to let your software die* * part of

    your software 01. 02. Without bringing the remaining parts with it 03. Write code that is easy to delete, not easy to extends A natural process that cannot be stopped

17. But that can be slowed down A natural process that

    cannot be stopped

18. That can be speeded up or slowed down Why does

    it appear? Refactoring helps to keep complexity under control 01. 02. A good software design is critical in the long term 03. Technical debt ≠ legacy software, but it can accelerate the process

19. What do we do now ?

20. You need to have empathy, and take the time to

    understand the project's history What do we do now ?

21. Strategies at the code level Legacy Code

22. Would you rather go to the dentist twice a year

    or brush your teeth every day? When to refactor

23. When to refactor Always leave the campground cleaner than you

    found it.

24. Always leave the campground cleaner than you found it. When

    to refactor This is the « boy scout rule » 01. 03. When you found a bug, first write a test that triggers it, then fix it. Developing a new feature and refactoring doesn’t mix well! 02. 04. Beware of the broken windows syndrome

25. Culture emerge from practices, not the other way around. When

    to refactor

26. Stop the weekly technical debt repayment session When to refactor

27. Stop the weekly technical debt repayment session When to refactor

    The « We’ll fix it later » syndrome 01. 02. The same cause always produces the same effect Instead provide a learning time, so you stop writing legacy code 03.

28. The big bang refactoring

29. The mikado™ method How to refactor

30. The mikado™ method How to refactor Undo when an experiment

    fail

31. The golden master Testing How to refactor

32. The golden master Testing « In nearly every legacy system,

    what the system does is more important that what it’s supposed to do. » — Michael Feathers How to refactor

33. The Hotspot™ method How to refactor

34. The Hotspot™ method How to refactor

35. The Hotspot™ method How to refactor

36. The Hotspot™ method How to refactor

37. Strategies at the system level Legacy system

38. Refactoring ? How to tackle it?

39. Refactoring ? How to tackle it?

40. Rewrite ? How to tackle it?

41. Rewrite ? How to tackle it?

42. The Ship of Theseus strategy How to tackle it?

43. The Ship of Theseus strategy How to tackle it?

44. Ask your business to help you map your (business) domain

    01. Invoice Generation Invoicing Car rental

45. Starting from your existing system Don’t start from your existing

    system

46. Ask them to tag where there is room for improvement.

    02. Invoice Generation Invoicing Car rental

47. Select a tagged support service with few dependencies 03. Invoice

    Generation Invoicing

48. Starting with your core business Don’t start with your core

    business Invoice Generation Invoicing Car rental !

49. Starting with your core business Don’t start with your core

    business Too many legacy dependencies 01. 02. The developers will need some training…

50. Don’t do horizontal slicing ! Don’t do horizontal slicing UI

    Persistence Business !

51. Don’t do horizontal slicing ! UI Persistence Business Do vertical

    slicing

52. Rewrite it… 04. Invoice Generation Invoicing New invoice Generation

53. And put an anti-corruption layer to prevent legacy leakage 05.

    Invoicing New invoice Generation Legacy API Legacy Database New Api ACL

54. The Anti-Corruption Layer Anti-Corrupution Layer The Greenfield code must not

    call directly the Legacy code 01. 02. The Legacy code must not call directly the Greenfield code 03. Even through the persistence system: database or event/message bus

55. Invoicing New invoice Generation Legacy DB Event bus Hidden dependencies

56. Invoicing New invoice Generation Legacy DB Event bus

57. Our system Vendor API ACL An anti-corruption layer can also

    protect us from the outside world

58. Invoice Generation Invoicing New invoice Generation Replace the old legacy

    system 06.

59. Invoice Generation Invoicing New invoice Generation Diff system Error Log

60. Repeat 07. Invoice Generation Invoicing Car rental

61. Until you can reach the core 08. Invoice Generation Invoicing

    Car rental

62. This strategy is also known as the Strangler pattern How

    to tackle it?

63. This strategy is also known as the strangler pattern How

    to tackle it? You’ll need to coordinate your actions at the system level 01. 02. Beware of functional debt 03. Optimise your new system for replacement!

64. • The Mikado method (Ola Ellnestam; Daniel Brolund) • Software

    Design X-Rays (Adam Thornhill) • Working Effectively with Legacy Code (Michael C. Feather) • Refactoring (Martin Fowler) • Accelerate (Jez Humble; Nicole Forsgren; Gene Kim) Going further Thanks to Cyrille Martraire, Thomas Pierrain, Jean-Baptiste Dusseaut, Adrian Bolboaca

65. Hello, I am a software developer. My name is Arnaud

    LEMAIRE, and you can find me on lilobase.me & @lilobase Thanks

66. https://roti.express/r/atbdx20 Feedback ?