This week’s podcast features a chat with Vitor Olivier. Olivier is a partner at NuBank (a technology-centric bank in Brazil). This podcast hits on topics from several of Nubank’s recent QCon talks and includes things like: Nubank’s stack, functional programming, event sourcing, defining service boundaries, recommendations on reasoning about services, tips (or tweaks) on the second iteration of their initial architecture and more.

Key Takeaways Property-based testing and Schemas (or Clojure.Spec) are complementary.

Clojure’s functional nature and Datomic’s features are a match for Nubank’s requirements.

A (micro)service needs to be able to create the full representation of the core feature it’s handling.

GraphQL is useful to abstract away the distributed system complexity from the mobile (or frontend) developers.

NuBank’s uses a combination of monitoring and sanity checks in real time at various levels to keep systems consistent. Once an invariant is broken, the system will try to fix it automatically.

Event sourcing architecture offers time-series debugging and improves confidence in the system.

Show Notes 1:24 - What is Nubank?

2:32 - Compete by continuously improving the product.

4:15 - Functional programming a good fit for banking logic.

5:30 - Datomic as persistence layer.

8:03 - Consistency considerations.

9:17 - Accounting view of the world. Maintaining consistency between Nubank’s microservices through monitoring and sanity checks in real time at various levels.

14:30 - Functions get applied to incoming events, stored in temporary version of database; perform sanity checks. If sanity checks pass, the changes are committed, if not, check which invariants are broken and try to fix automatically.

16:12 - Property-based (or generative) testing to find corner cases. Schemas exist for various types and can be used to generate tests.

19:12 - Why use Clojure? Because of Datomic. Clojure makes imperative code look bad; it's useful to stick to functional practices.

21:08 - The Nubank team.

25:14 - Lessons learned building microservices, both building services that did either too much or services that could have been combined into one.

27:18 - How to choose boundaries for microservices. A service needs to be able to create the full representation of the core feature it’s handling.

34:39 - How Nubank uses GraphQL. Abstracts away the distributed system complexity from the mobile developers. Resources Olivier’s talk at QCon NYC goes into detail on the Nubank architecture

Nubank’s Edward Wible and Rafael Ferreira talk on Nubank

A sample of talks about Property-based testing Property-based Testing in Practice Better Tests, Less Code: Property-Based Testing



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