This document discusses the challenges of building reliable banking architectures in the cloud and how Starling Bank addressed this issue. It introduces some key concepts like distributed architectures, self-contained systems, and the DITTO architecture which focuses on idempotency and eventual consistency. The benefits of this approach for Starling Bank included safe instance termination, continuous delivery of backend changes up to 5 times a day using chat-ops releases, and the ability to "chaos test" to ensure reliability.

1. BANKING IN THE CLOUD:
ULTRA-HIGH RELIABILITY
ARCHITECTURES
Jason Maude - Head of Technology Advocacy
@jasonmaude

2. THE PROBLEM
WITH BANKING

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

4. “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

5. A tale of banking woe

6. If you develop, you break things

7. WHO ARE
STARLING BANK?

8. 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

9. 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

10. BUILDING
RELIABLE
ARCHITECTURE

11. Why not the monolith?

12. Recovery in distributed architectures

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

14. Self-contained systems

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

16. DITTO architecture
(do idempotent things to others)

17. 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

18. THE BENEFITS
OF DITTO
ARCHITECTURE

19. Instance termination is safe

20. Continuous(ish) 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

21. Chat-ops releases

22. 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

23. … and if something goes wrong...

24. Chaos

25. IN CONCLUSION

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