Legacy Code: Evolve or Rewrite?
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The document discusses the dilemma between evolving legacy code versus rewriting it, emphasizing the importance of surrounding legacy systems with tests and identifying critical boundaries for potential rewrites. It presents strategies like the strangler application and feature toggles to progressively replace legacy functionalities while maintaining business differentiation. The author advocates for understanding the application thoroughly and integrating new knowledge effectively to minimize risks and maximize value delivery.
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[primary flow & support features]
http://www.fimarkets.com/pagesen/back-middle-front-office.php](https://image.slidesharecdn.com/legacycodeevolveorrewrite-141001153310-phpapp02/85/Legacy-Code-Evolve-or-Rewrite-65-320.jpg)
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[primary flow & support features]
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[primary flow & support features]
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![Main concepts
[in selling-something business]
Trading
Financial
Instruments](https://image.slidesharecdn.com/legacycodeevolveorrewrite-141001153310-phpapp02/85/Legacy-Code-Evolve-or-Rewrite-71-320.jpg)
![Main concepts
[in selling-something business]
Trading
Financial
Instruments
DON’t
TOUCH
REWRITE](https://image.slidesharecdn.com/legacycodeevolveorrewrite-141001153310-phpapp02/85/Legacy-Code-Evolve-or-Rewrite-72-320.jpg)
![Agree on maxims
[communicate the plan]
• “Only one
work site at
a time:
instruments”
!
• “When in
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Legacy Code: Evolve or Rewrite?
- 1. Legacy Code Evolve or Rewrite ? A retrospective Cyrille Martraire - @cyriux -
- 3. Passionate developer PARIS Since 1999 ! @cyriux
- 4. Paris Software Craftsmanship Community http://www.meetup.com/paris-software-craftsmanship/
- 5. TDD BDD DDD Legacy
- 7. LEGACY
- 8. Legacy: Evolve or rewrite?
- 10. Once upon a time…
- 11. There was a frustrated ambition
- 12. We Want:
- 13. Large Ambition
- 14. Asset Management
- 16. wanna do big things stuck with a legacy
- 17. So what do we do?
- 18. REWRITE
- 19. STOP!
- 20. We all want to rewrite
- 22. hard to release regressions
- 23. Legacy
- 24. Legacy No Test & Technical Debt too
- 26. Plenty of Legacy code working since 1993 Redoing = Waste + Risk
- 27. Poorly designed code Working well Never changed Is OK
- 28. KEEP iT
- 29. KEEP GUI, DB, APP Server, middleware
- 30. We Want NEW FEATURES! CHANGE SOMETHING
- 31. Haz Change?
- 32. JUST DO IT!
- 33. QUICK
- 34. Did we break something?
- 36. Takes a lot of time No Test + Debug!
- 37. Just Do It: Not that quick Again and again
- 38. Could we do better?
- 39. EVOLVE
- 40. Surround with tests FIRST
- 43. Testing legacy code is hard & slow
- 44. Testing is an investment
- 45. Driver = Cost of testing
- 46. A matter of velocity
- 47. Legacy testing effort Vs. All new tested code? Is it worth it?
- 48. 1:4 (Ok, I totally made it up) ratio
- 49. REDO
- 50. Differentiating to the business?
- 51. The CEO will tell you
- 53. BUY
- 55. Differentiating!
- 56. REWRITE
- 57. "What if we also rewrote this crappy part?" • Why not, but not now • Don't get lost redoing everything forever
- 58. ...
- 59. JUST ENOUGH
- 60. You can rewrite You cannot rewrite all
- 61. What to rewrite? Where to stop?
- 63. What to rewrite? Find boundaries
- 64. Discover the app ! ! Read the documents Interview people Use the application Read the code Fix bugs
- 65. Visualize [primary flow & support features] http://www.fimarkets.com/pagesen/back-middle-front-office.php
- 66. Visualize [primary flow & support features] http://www.fimarkets.com/pagesen/back-middle-front-office.php
- 67. Visualize [primary flow & support features] http://www.fimarkets.com/pagesen/back-middle-front-office.php
- 69. Asset Capture Transmission Exhaust http://martinfowler.com/bliki/AssetCapture.html Engine
- 70. Asset Capture Transmission Exhaust Focus on one single asset : the engine http://martinfowler.com/bliki/AssetCapture.html Engine
- 71. Main concepts [in selling-something business] Trading Financial Instruments
- 72. Main concepts [in selling-something business] Trading Financial Instruments DON’t TOUCH REWRITE
- 73. DOMAIN FTW!
- 75. Agree on maxims [communicate the plan] • “Only one work site at a time: instruments” ! • “When in Rome, do as Romans do”
- 76. "The code says it all"
- 77. Legacy: Fossilized Domain Expertise •inspiration •obfuscated http://newspaper.li/fossil/
- 78. Rewrite: ! because of CHANGES (or it’s a bad idea)
- 79. needs
- 80. Rewrite: ! must inject NEW knowledge
- 81. Rewrite: ! need business ANALYSIS
- 82. WHOLE TEAM
- 83. Like a new project from scratch!
- 84. So how do we integrate?
- 85. STRANGLE
- 86. Strangler application A new module will progressively strangle the former one, for one single asset only http://martinfowler.com/bliki/StranglerApplication.html http://www.flickr.com/photos/louisfoecy/4114597043
- 87. Feature Toggles ! Progressively turn off legacy functionalities & turn on the new ones OLD NEW
- 88. if(c == category1) {legacy.compute(...)} else if(c == category2) {strangler.compute(...)} //...
- 89. Grow a Bubble Context
- 90. ! Listen to domain experts High hygiene standards Pair-programming TDD, BDD, DDD
- 91. Invest in domain knowledge • Bi-weekly 30mn training sessions
- 92. Dream model must pass every scenario Given a floating rate bond on EURIBOR 3M And a nominal of 15M EUR And an issue date of 2011/06/15 And an end date of 2012/06/14 And an SEMI_ANNUAL calculation period ! When the EURIBOR 3M evolves: Bespoke custom DREAM MODEL | 2011/09/15 | 3.5% | | 2012/03/15 | 4.0% | ! Then the cash-flows are: | 2011/12/13 | 23000 | | 2012/06/14 | 25500 |
- 94. Adapter
- 95. API SPI
- 96. Easier to integrate by construction bespoke lib
- 97. Old code: Freeze it
- 98. Rewrite = clear boundaries + new strangler application + minimal integration
- 101. Questions? Did you try similar things too? Let’s discuss! @cyriux
- 102. Follow me @cyriux ! Slides: slideshare.net/cyriux Blog: cyrille.martraire.com ! In Paris? Join !
- 103. Merci