KanDDDinsky Berlin 2017: Let Your Domain Events Flow

Transcript

1. Let your domain events flow KanDDDinsky, Oct 20th, 2017, Berlin, Germany mail@bernd-ruecker.com martin.schimak@plexiti.com With thoughts from http://flowing.io @berndruecker | @martinschimak
2. Bernd Rücker Consultant & Dev. Advocate 10+ years workflow Co-founder Camunda http://bernd-ruecker.com/ Martin Schimak Developer & Trainer, 10+ years (de-)coding domain knowledge DDDesign, TDD/BDD, EDA http://plexiti.com/ http://flowing.io/
4. Simplified example: dash button Photo by 0xF2, available under Creative Commons BY-ND 2.0 license. https://www.flickr.com/photos/0xf2/29873149904/
5. Three steps…
6. Who is involved? Checkout Payment Inventory Shipment
7. Looking into events… Checkout Payment Inventory Shipment Domain Events are facts that happened in the past Good Fetched Good Stored Read Model Write Model „The button blinks green if we can ship the item within 24 hours!“
8. Peer-to-peer event flows Checkout Payment Inventory Shipment Payment received Order placed Goods fetched
9. Peer-to-peer event flows Checkout Payment Inventory Shipment Payment received Order placed Goods fetched Please fetch the goods before waiting for payment Some customers can pay via invoice …
10. Some requirements don‘t fit anywhere… What are we missing? Order Checkout Payment Inventory Shipment
11. Commands can decrease coupling Order Checkout Payment Inventory Shipment Order placed Retrieve payment Commands have an intent about what needs to happen in the future Please fetch the goods before waiting for payment Some customers can pay via invoice Payment received Retrieve payment
12. Good API design respects responsibility boundaries Order Checkout Payment Inventory Shipment „A few smart god services tell anemic CRUD services what to do!” Sam Newman What is the payment service responsible for?
13. Some things in life take time
14. A customer can update an expired credit card within two weeks before we cancel his order „
15. Payment requires persitent state Order
16. Pass around state as „routing slip“ Persist state with Entity, Actor, … State machine How to implement a Process Manager? DIY DIY
17. State machine Persistent thing (Entity, Actor, …) Routing slip CADENCE Baker
18. State machines solve some hard developer problems Monitoring & Operations Handling of time & timeouts Retry Visibility & Reporting Versioning Compensation Message correlation & deduplication Performance & scalability
19. Leaving the aggregate scope?
20. State machines solve some hard developer problems Monitoring & Operations Handling of time & timeouts Retry Visibility & Reporting Versioning Compensation Message correlation & deduplication Performance & scalability
21. Bpmn.createProcess("order").executable() //... .sendTask().name("Retrieve payment").camundaClass(RetrievePayme .receiveTask().name("Payment received").message("PaymentReceive //... { "name": "retrieve_payment", "tasks": [ { "name": "Retrieve Payment", "taskReferenceName": "payment", "type": "SIMPLE", ... Do you prefer coded or graphical DSLs? * BPMN - ISO notation for modeling and executing long-running processes and flows
22. Do you need a timeout?
23. Do you need a compensation? *
24. BPM?
25. Flows done right Developer friendly Lightweight & composable BizDevOps
28. More complex flows - transparent and directly executable
29. Specifying and testing long-running behaviour
30. A visual test report for example #1 (Balance = 50, Amount = 70)
31. A visual test report for example #3 (Balance = 50, Amount = 30)
32. The binding strategy uses the step only when required
33. Living documentation for long-running behaviour
34. Explicit language help in tackling complex event flows Ubiquitous Language Software Experts Domain Experts
35. Explicit flows help sepatrate domain and infrastructure Ports and Adapters Application Domain Aggregates, Domain Events, Domain Services, etc … + the flow State machine
36. Flows live inside the context boundaries
37. Example Inventory Payment Order Shipping Checkout Monitor https://github.com/flowing/flowing-retail/ Human Tasks
38. Live hacking
39. Operational visibility in monitoring – possibly end-to-end
41. Mitigate tight coupling Consider core capabilities Leverage state machines Decentralize
42. Thank you!
43. Code online: https://github.com/flowing Slides & Blog: https://bernd-ruecker.com https://plexiti.com With thoughts from http://flowing.io @berndruecker | @martinschimak https://www.infoq.com /articles/microservice- event-choreographies
44. Images licensed from iStock no attribution required All icons licensed from Noun Project no attribution required Images licensed under Creative Commons license Photo by 0xF2, available under Creative Commons BY-ND 2.0 license. https://www.flickr.com/photos/0xf2/2987 3149904/