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Le projet legacy, quelles stratégies pour s'en ...

Le projet legacy, quelles stratégies pour s'en sortir ? – Software Crafts·wo·manship Rennes juin 2021

Arnaud LEMAIRE

June 17, 2021
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  1. A code you want to change, that no one understands

    but still provides value. De fi nition
  2. A code without predictability De fi nition 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
  3. A code with no test De fi nition « 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
  4. Hello, I work in the fi nance industry at Sunday.app.

    My name is Arnaud LEMAIRE, And my twitter handle is @lilobase Who am I?
  5. A natural process Why does it appear? Add lines of

    code More complexity Increase in software entropy Legacy Code
  6. You need to let your software die* * a part

    of your software 01. 02. Without bringing the remaining parts with it 03. Optimize your software for replacement A natural process that cannot be stopped
  7. 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
  8. You need to have empathy, and take the time to

    understand the project's history What do we do now ?
  9. Would you rather go to the dentist twice a year

    or brush your teeth every day? When to refactor
  10. 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, fi rst write a test that triggers it, then fi x it. 04. Beware of the broken windows syndrome Developing a new feature and refactoring doesn’t mix well! 02.
  11. Stop the weekly technical debt repayment session When to refactor

    The « We’ll fi x 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.
  12. 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
  13. The golden master Testing « A Gold Master test is

    a regression test for complex, untested systems that asserts a consistent macro-level behavior. » — Jake Worth How to refactor
  14. Ask your business to help you mapping your (business) domain

    01. Invoice Generation Invoicing Car rental
  15. Ask them to tag where there is room for improvement.

    02. Invoice Generation Invoicing Car rental
  16. And put an anti-corruption layer to prevent legacy leakage 05.

    Invoicing New invoice Generation Legacy API Legacy Database New Api ACL
  17. The Anti-Corruption Layer Anti-Corrupution Layer The Green fi eld code

    must not call directly the Legacy code 01. 02. The Legacy code must not call directly the Green fi eld code 03. Even through the persistence system: database or event/message bus
  18. The Ship of Theseus strategy 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. Optimize your new system for replacement!
  19. Starting by your core business Mistakes to avoid Too many

    legacy dependencies 01. 02. The developers will need some training…
  20. • The Mikado method • Software Design X-Rays • Working

    E ff ectively with Legacy Code • Refactoring Going further Thanks to Michael C. Feather, Adam Thornhill, Cyrille Martraire, Thomas Pierrain, Martin Fowler, Jean-Baptiste Dusseaut, Ola Ellnestam, Daniel Brolund, Adrian Bolboaca
  21. Thank you! I work in the fi nance industry at

    Sunday.app. My name is Arnaud LEMAIRE, And my twitter handle is @lilobase