Video and slides synchronized, mp3 and slide download available at URL https://bit.ly/2FNfhjM. Jason Maude talks about the experience of Starling Bank, a mobile-only, cloud-based bank that launched in the UK in 2017. He looks at the system architecture of the bank, the design principles that give them the ability to release quickly and reliably, and why they decided to build the back end using Java. Filmed at qconsf.com. Jason Maude has over a decade of experience working in the financial sector, primarily in creating and delivering software. He is passionate about creating teams and explaining complex technical concepts to those who are convinced that they won't be able to understand them. He currently works at Starling Bank as one of their lead engineers and host of the Starling podcast.

1. BUILDING A RELIABLE CLOUD
BASED BANK IN JAVA
Jason Maude - Senior Engineer
@jasonmaude

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Watch the video with slide
synchronization on InfoQ.com!
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starling-bank

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4. THE PROBLEM
WITH BANKING

5. “Move fast and break things. Unless you are
breaking stuff you are not moving fast
enough.”
Mark Zuckerberg

6. “Gringotts was the safest place in the world
for something you wanted to hide”
Harry Potter and the Philosopher's Stone by J K Rowling

7. A tale of banking woe

8. If you develop, you break things

9. WHO ARE
STARLING BANK?

10. Who are Starling Bank?
• Tech start-up with a banking licence
• ~100% cloud-based, mobile-only
• Mastercard debit card
• DDs and faster payments
• Location-enriched transaction feed
• ApplePay, GooglePay, FitBitPay...
• Spending insights
• Granular card control
• Open APIs & developer platform

11. We built a bank in a year
• Jan 2014 - Founded by Anne Boden
• Jun 2014 - Kick-off with Regulators
• Sep 2015 - Technical prototypes
• Jul 2016 - Granted a partial banking license
• Nov 2016 - Launching the alpha app
• Feb 2017 - Launching the beta app
• Apr 2017 - Granted a full banking license
• May 2017 - Public launch
• Mar 2018 - Awarded Best British Bank

12. BUILDING
RELIABLE
ARCHITECTURE

13. Self-contained systems
http://scs-architecture.org

14. Self-contained systems

15. Recovery in distributed architectures

16. L.O.A.S.C.T.T.D.I.T.T.E.O.

17. DITTO architecture
(do idempotent things to others)

18. DITTO architecture
• Do everything at least once and at most once
• Retry (at least once)
• Idempotency (at most once)
• Work towards correctness, eventual consistency
• Reduce synchronicity to a minimum
• Save all requests to the database first
• Keep the smarts in the services, not in the pipes
• No distributed transactions
• Do not trust other services

19. POST
201 Created {uuid}
PUT {uuid}
202 Accepted
PUT {uuid}
202 Accepted
paymentcustomer bank
Make a
payment
DITTO in action

20. POST
PUT {uuid}
paymentcustomer bank
PUT {uuid}
202 Accepted
retry Idempotency provides “at most once”
Retry provides “at least once”
202 Accepted
retry
PUT {uuid}
PUT {uuid}
201 Created {uuid}

21. Catch-up processing
Catch Up
Processor
RC
RC
RC

22. But why Java?
• Exceptions are noisy and difficult to ignore
• Reliable ecosystem (user base, tooling, job market, etc)
• Integrations with legacy third parties (SOAP etc)

23. THE BENEFITS
OF DITTO
ARCHITECTURE

24. Instance termination is safe

25. Continual delivery of back-end
• Continual deployment to non-prod, sign-off into prod
• Auto build, dockerise, test, scan, deploy < 1h
• Code released to production up to 5 times a day

26. Bi-modal banking IT
• Incumbent banks operate:
- legacy backends that move at glacial pace
- … and try to iterate the customer experience faster
• We release the backend at 10x the rate of the mobile apps
- 1-5 backend software releases per day
- 1-2 infrastructure releases per day
- mobile apps released weekly or fortnightly

27. The “rolling” giphy
• Our auditors loved this one
• Yes it’s in our release documentation
• Clear signal in engineering channel that is release in progress

28. … and if something goes wrong...

29. Testing
• Chat-ops via Slack
• Available to all developers

30. Chaos

31. THE FUTURE

32. DITTO at scale: Self DOS
Catch Up
Processor

33. DITTO at scale: Racing to work

34. The future of the JVM
• Java as an ecosystem
• Is the upgrade to Java 9/10/11 worth it?
• Could someone else steal the crown?

35. SOME
IMPORTANT
TAKEAWAYS

36. Design software to be skeptical

37. Give EVERYTHING a UUID

38. Fire alarms are good

39. You can do anything you can undo

40. Thank you!
Check out the Starling Developer Podcast!
https://developer.starlingbank.com
@jasonmaude

41. Watch the video with slide
synchronization on InfoQ.com!
https://www.infoq.com/presentations/
starling-bank