MuCon London 2017: Break your event chains

1. Break your event chains MuCon, November 6th 2017, London 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/

3. 3 common hypotheses we check today: # Events decrease coupling # Central control needs to be avoided # Workflow engines are painful

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. Basic idea of dedicated, autonomous (micro-) services Checkout Payment Inventory Shipment Dedicated Application Processes Dedicated Persistence Backends Dedicated Development Teams

8. Events decrease coupling

9. Request/Response: temporally coupled services Checkout Payment Inventory Shipment „The button blinks green if we can ship the item within 24 hours!“ Request Response

10. Events: temporal decoupling with read models Checkout Payment Inventory Shipment „The button blinks green if we can ship the item within 24 hours!“ Events are facts about what happened (in the past) Good Fetched Good Stored Read Model

11. Events: Extract cross-cutting aspects Checkout Payment Inventory Shipment „Inform the customer about steps he is interested in!“ Order placed Payment received Good shipped Notify me when … Order placed Payment received Good fetched Good shipped Customer Mailings Good fetched

12. Events can decrease coupling* *e.g. decentral data-management, read models, extract cross-cutting aspects

13. Events: peer-to-peer event choreographies Checkout Payment Inventory Shipment Order placed Payment received Good shipped „When the button is pressed, an order is placed - and fulfilled!“ Good fetched

14. Events: peer-to-peer event choreographies Fetch the goods before retrieving the payment Some customers can pay via invoice … Checkout Payment Inventory Shipment Good fetched Order placed Payment received Good shipped

15. Extract the end-to-end responsibility Order Checkout Payment Inventory Shipment Order placed Retrieve payment Commands have an intent about what needs to happen in the future Fetch the goods before retrieving the payment Some customers can pay via invoice Payment received Retrieve payment

16. Events can increase coupling* *e.g. complex peer-to-peer event chains

17. Commands can decrease coupling* *e.g. to avoid complex peer-to-peer event chains

18. Central control needs to be avoided

19. Checkout Payment Inventory Shipment Order Order placed Payment received Good fetched Good shipped Smart ESB-like middleware

20. Checkout Payment Inventory Shipment Order Dumb pipes „Smart endpoints and dumb pipes!” Martin Fowler

21. The danger of god services Checkout Payment Inventory Shipment Order „A few smart god services tell anemic CRUD services what to do!” Sam Newman „Central“ order service as bad as central ESB logic?

22. A god service is only created with bad API design Checkout Payment Inventory Shipment Order „Smart endpoints and dumb pipes!” Martin Fowler Smart endpoints take care of a business capability their client does not need to understand.

23. Ask: who is responsible to deal with problems? Order Credit Card Retrieve Payment Expired A single central client of dumb endpoints becomes a god service. Better: we create several decentral, smart endpoints. „If the credit card expired, the customer gets another chance to provide new card details!“

24. Ask: who is responsible to deal with problems? Order Credit Card „If the credit card expired, the customer gets another chance to provide new card details!“ Expired „Smart endpoints are potentially long-running.” Payment Retrieve Payment Payment received „The client of a smart endpoint remains lean.”

25. Be sceptical about central control!* *e.g. centralized ESB-like components or god services which heavily interact with dumb endpoints

26. But don‘t give up control!* *e.g. miss to extract and control important potentially long-running business capabilities

27. The problem is not to command services! The problem is bad API design.

28. Workflow engines are painful

29. Persist thing with Entity, Actor, … State machine or workflow engine DIY Order Credit Card Payment Payment received How to implement long- running services?

30. State machines or workflow engines CADENCE Baker

31. Workflow engines solve some hard developer problems Monitoring & Operations Handling of time & timeouts Retry Visibility & Reporting Versioning Compensation Message correlation & deduplication Performance & scalability

32. Distributed systems

33. Workflow engines solve some hard developer problems Monitoring & Operations Handling of time & timeouts Retry Visibility & Reporting Versioning Compensation Message correlation & deduplication Performance & scalability

34. Workflow and BPM

35. 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

36. Timeouts

37. Compensation*

38. Living documentation for long-running behaviour

39. Focus on long-running behaviour - requiring state

40. A visual HTML report for a specific test case

41. Workflows live inside service boundaries

42. Explicit flows help separate domain and infrastructure Infrastructure Aggregates, Domain Events, Domain Services, etc … + the flow Workflow Engine Payment Application Domain

43. Lightweight workflow engines are great (and much better than DIY)* *e.g. enabling potentially long-running services, solving hard developer problems, can run decentralized

44. Workflow engines can do (service) orchestration.* Orchestration is not about synchronous request/response! *We are not talking about container orchestration

45. # Events decrease coupling: sometimes read-models, no complex peer-to-peer event chains, don‘t forget commands # Central control needs to be avoided: sometimes no ESB, smart endpoints/dumb pipes, important capabilities need a home # Workflow engines are painful: some of them lightweight engines are easy to use and can run decentralized, they solve hard developer problems, don‘t DIY

46. Need some code? InventoryPaymentOrder ShippingCheckout Monitor https://github.com/flowing/flowing-retail/ Human Tasks

47. Thank you!

48. 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

49. 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/

MuCon London 2017: Break your event chains

Bernd Ruecker

MuCon London 2017: Break your event chains