Exploring Alternatives to CRUD apps with CQRS and Event Sourcing

Ever wonder what your web app might look like if you choose not to build a CRUD app? This talk will explore alternatives to CRUD by examining concepts of domain driven design, along with CQRS and event sourcing. We will dive into specific examples with the Axon framework for Java. This talk will compare and contrast CRUD applications to CQRS style architectures and what their application can look like when combined with domain driven design and event sourcing. We will go over the benefits as well as some of the complexities and challenges encountered when using this pattern.

1. Leave your ‘cruddy’ app behind: Exploring Alternatives to CRUD apps with CQRS and Event Sourcing
2. I’m Amber, Software Developer at ThoughtWorks @amber_ht
3. ➔ What is CQRS? ➔ Event Sourcing + CQRS + DDD ➔ Some of the benefits ➔ Demo time ➔ What to watch out for - complexities
4. C R U D reate ead pdate elete
5. C Q R S ommand uery esponsibility egregation
6. ➔ Large financial institution Experience with CQRS + Event Sourcing ➔ > 70 people ➔ ~ 7 teams ➔ Distributed across 2 continents
8. Datastore Data Access Domain Logic Presentation Layer All Fries Poutine Delivery
9. @POST /orders Order @POST /orders/id/items @POST /orders/id/items @DELETE /orders/id/items/itemId @PUT /orders/id Order Promo Code
10. Datastore Data Access Domain Logic Presentation Layer All Fries Poutine Delivery
11. @PUT /orders/id Update Order
12. DELETE ORDER vs CANCEL ORDER
13. UPDATE CUSTOMER vs REGISTER CUSTOMER FOR PROMOTION
14. not so fast writes Very very fast reads? vs
15. Twitter 300K requests / s reads 6k requests / s writes vs 50x more reads than writes http://highscalability.com/blog/2013/7/8/the-architecture-twitter-uses-to-deal-with-150m-active-users.html
16. ➔ Audit Log? Analytics? ➔ Capturing the users intent ➔ De-coupling write and read operations
17. Presentation Layer Domain Logic / Command Model Data Access / Query Model Command Query Datastore Datastore
18. “Event Sourcing ensures that all changes to application state are stored as a sequence of events.” - Martin Fowler
19. UI Command Query Command Command Handler Aggregate Root Event Event Listener Datastore Read Side Model Query Datastore
20. OrderOpenedEvent PoutineAddedToOrderEvent PoutineAddedToOrderEvent PoutineRemovedFromOrderEvent PromoCodeAppliedEvent Event Store
21. Benefits of CQRS + Event Sourcing + DDD ➔ Immutable Event Store ◆ Built in Audit Logs ◆ Replayable events to re-build current state ➔ Ubiquitous language ➔ Loose coupling of components ➔ Traceable errors
22. In the real world, our actions extend beyond creating, reading, updating and deleting things. So why limit the way we design software to these four actions?
23. Accounts Service Shipping Service Order Service Payments Service AccountOpenedEvent
24. Demo
25. www.axonframework.org
26. https://github.com/amber-h/axon-fullstackTO
27. ➔ Suitable with complex business domain Things to keep in mind... ➔ Scalability of read operations ➔ Built in audit logs ➔ Does not need to be used in all components of your system!
28. What to watch out for? Complexities...
29. Evolving Events
30. PoutineAddedToOrderEvent ItemAddedToOrderEvent
31. PoutineAddedToOrderEvent V1 V2
32. OrderOpenedEvent PoutineAddedToOrderEvent PoutineRemovedFromOrderEvent PromoCodeAppliedEvent Event Store LineItemAddedToOrderEvent PoutineAddedToOrderEvent LineItemAddedToOrderEvent
33. Upcasting “Is the mechanism used to convert deprecated (typically serialized) objects and convert them to the current format” - Axon Docs
34. ➔ Event replay in practice ➔ Eventual Consistency ➔ Upcasting Other things to watch out for... ➔ Not as many tools & resources
35. References ➔ http://martinfowler.com/bliki/DDD_Aggregate.html ➔ CQRS and Event Sourcing - Greg Young ◆ https://www.youtube.com/watch?v=JHGkaShoyNs ➔ Avoiding monolith applications with Axon Framework - Trifork ◆ https://www.youtube.com/watch?v=g2A_e9jH0No ➔ Axon 3 Live Coding Webinar - Trifork ◆ https://www.youtube.com/watch?v=s2zH7BsqtAk
36. Thank You github.com/amber-h/axon-fullstackTO @amber_ht