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Event Storming, DDD, Reactive Systems, and Microservices


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Talk from microxchg Berlin 2018 -

Published in: Software

Event Storming, DDD, Reactive Systems, and Microservices

  1. 1. Designing Reactive Systems with Event Storming
  2. 2. DDD and Microservices Great: Some Boundaries Strategic - Bounded Contexts Payments Shipping
  3. 3. DDD and Microservices Great: Some Boundaries Tactical - Aggregates Booking
  4. 4. DDD and Microservices Not so great: Too much focus on structure Noun Obsession Boundaries yes - but sometimes these are poorly chosen
  5. 5. DDD and Microservices Better: Events First „It is not the things that matter in early stages of design… …it is the things that happen.“  Russ Miles
  6. 6. Microservices DDDEventStorming
  7. 7. EventStorming Start with Events Seat selected
  8. 8. EventStorming Only then - explore what triggers these events, add commands Seat selected Choose seat
  9. 9. EventStorming Only then start thinking about aggregates. Seat selected Choose seat Booking
  10. 10. EventStorming Let aggregates emerge - don’t jump to conclusions. Seat selected Choose seat Seat map
  11. 11. EventStorming First publication - 2013? Impression, not empirically backed: Has quickly become very popular for „big picture“ analysis - not (yet) so much for modelling services.
  12. 12. EventStorming Challenge
  13. 13. Reactive Systems
  14. 14. The Supertrend in Microservices
  15. 15. Events vs. Messages Message: Directed, has a recipient. Event: Undirected, is emitted and picked up by interested parties. Not important for our discussion, please ignore.
  16. 16. Microservices vs. Reactive Systems Microservices are about isolation, speed of change, agility. Reactive Systems are about scalability, reliability. Microservices and Reactive Systems complement each other, the goal is to build Reactive Microservices.
  17. 17. Actors
  18. 18. Actor libraries & frameworks
  19. 19. Async HTTP Stack, REST/JSON support built-in
  20. 20. Persistence through 
 Event Sourcing/ CQRS Event Event Event Command A A'
  21. 21. Each service can be clustered. Node A Node B Node C X B A Z X Y N M
  22. 22. Kafka integrated as messaging backbone.
  23. 23. „Going to microservices is like going from Newton’s physics to Einstein’s physics. Newton’s time marched forward uniformly with instant knowledge at a distance. Before microservices, distributed computing strove to make many systems look like one with RPC, 2PC etc.. In Einstein’s universe, everything is relative to one’s perspective.“ Pat Helland
  24. 24. Event Storming to the Rescue! +
  25. 25. Reactive Systems & Event Storming Event Storming model elements map 1:1 to implementations e.g. in Lagom Event -> Event Command -> Command Aggregate -> Persistent Entity keeping the model and implementation aligned
  26. 26. Reactive Systems & Event Storming It goes so far that it’s actually encoded in types.. Aggregate Command Event
  27. 27. Event Storming for Reactive Microservices Maybe you don’t see the beauty of it, let me quote the Blue Book again…
  28. 28. Summary event storming is not only for „big picture“ analysis. you can do event storming on different levels, including modelling services.
  29. 29. Summary The biggest obstacle for building truly reactive systems is not technology, the tools are there (e.g. actors). Instead, the challenge is in the design, which requires you to embrace the asynchronous, distributed nature. Event Storming as a modelling tool can help to overcome this obstacle.
  30. 30. Summary A message driven, actor based implementation not only has technical merit (as in being reactive), it’s also the „natural“ implementation for an event storming model, if you want model and implementation to align closely.
  31. 31. Experience it for yourself Shameless Self Promotion: Workshops (Mainz, 23.4.2018) microservices.html (Berlin, 14./15.5.2018)
  32. 32. Further Reading with-event-storming-and-ddd systems-with-event-storming-73c6236f5dd7