Business agility and legacy applications

Presentation at Agile Business Day 2017

Transcript

1. BUSINESS AGILITY AND LEGACY APPLICATIONS Matteo Vaccari @xpmatteo
2. We will buy your software! …if you implement X, Y and Z
3. …The ability to change quickly and cheaply What is business agility? 3 TURN ON A DIME… FOR A DIME Craig Larman
4. …Business agility depends on software agility Unfortunately… 4
5. Most valuable software is hard to change • It’s a tangle of IFs. It can only be changed by adding more IFs, thus making the situation worse. • Depends on a legacy DB, accessed by many apps and nobody is sure anymore what all the tables and columns are for. • Has a tangle of configuration options, and nobody is sure of which combination of options work correctly together. • Or worse, there are many forks, one per customer, and it is hell to backport new features to all forks
6. What does “easy to change” look like? 6
7. What does “easy to change” look like? … it is SIMPLE 7
8. What does “easy to change” look like? … it is SIMPLE 8
9. Ideally, we’d like to be able to… implement new features in new files 9 …without touching existing files
10. So… how do I refactor legacy code?
11. So… how do I refactor legacy code? YOU CAN’T.
12. Can I rewrite my legacy app then?
13. Can I rewrite my legacy app then? • Stop all new developments • Wait for 12-24 months • On day X we replace the old app • And voilà: it works
14. Can I rewrite my legacy app then? • Stop all new developments • Wait for 12-24 months • On day X we replace the old app • And voilà: it works
16. Strangler application Database nuovo App Nuova Database legacy App Legacy Batch Sync Utenti Apache Perl filter Utenti migrati Utenti non migrati Router Old and new apps Update mechanism
17. Strangler app antipatterns
18. The router is inside the legacy app BAD ⇒ have a separate router component Old App New App Batch sync
19. Sharing the same VM Old App New App ⇒ old and new should not share any resources BAD
20. The update mechanism is a new API in the old app Update Mechanism Old App New App Router ⇒ implement the update mechanism as a separate component BAD
21. The update mechanism is a separate component GOOD The old app is not aware of the new app Old App New App Router Update
22. The new app and the legacy should not be aware of each other! • Reduced need to involve the developers of the legacy • Reduced risk to break the legacy • You can start, test and change the new app on the developer machine, with no need to start or connect to the legacy So that strangulation is faster, safer and cheaper
23. twitter.com/xpmatteo thoughtworks.com THANK YOU WE ARE HIRING! YES, IN ITALY!