The Dark Side of Events (EDA)

Events are our industry’s near and dear. All technological conferences are full of talks on event sourcing, event driven architectures, or event driven integrations. So hey, why not make another one? …But a bit different: Let’s talk about the dark side of this pattern.

Events, as any tool, can be used productively or destructively. During the last 8 years, at Internovus, we found so many creative ways to do the latter:

* The different ways events can introduce coupling so strong, it will make the classic enterprise monolith envy
* Multiple ways of using events to introduce accidental complexity
* How to use events to turn a microservice into an architectural trojan horse; And
* Why some events, just like underwear, better be kept private

Those sights are not for the faint of heart, but fear not. You will get heuristics that will help you identify those situations, eliminate event-driven accidental complexities, and make events great again.

Transcript

1. vladikk doit-intl.com #ndcsydney THE DARK SIDE OF EVENTS
2. vladikk doit-intl.com #ndcsydney @vladikk vladikk.com DoiT International
3. vladikk doit-intl.com #ndcsydney
4. vladikk doit-intl.com #ndcsydney SOFTWARE ARCHITECTURE
5. vladikk doit-intl.com #ndcsydney "Architecture is about the important stuff, whatever that is” - Ralph Johnson
6. vladikk doit-intl.com #ndcsydney SOFTWARE SOLVES BUSINESS PROBLEMS GOOD DESIGN SUPPORTS THE BUSINESS
7. vladikk doit-intl.com #ndcsydney Infrastructure Databases Architectural styles Frameworks Languages Methodologies Accidental Complexity
8. vladikk doit-intl.com #ndcsydney …and it’s hard!!! GOOD DESIGN SUPPORTS THE BUSINESS SOFTWARE SOLVES BUSINESS PROBLEMS
9. vladikk doit-intl.com #ndcsydney THE GOAL OF SOFTWARE ARCHITECTURE IS TO MANAGE COMPLEXITY!
10. vladikk doit-intl.com #ndcsydney 1. Component level 2. System level 3. Implementation level Complexity Management
11. vladikk doit-intl.com #ndcsydney Local Complexity
12. vladikk doit-intl.com #ndcsydney Global Complexity
13. vladikk doit-intl.com #ndcsydney Global Complexity
14. vladikk doit-intl.com #ndcsydney ARCHITECTURE = BOUNDARIES DESIGN
15. vladikk doit-intl.com #ndcsydney
16. vladikk doit-intl.com #ndcsydney EVENTS AND THEIR TYPES
17. vladikk doit-intl.com #ndcsydney EVENT: CONTRACT FOR INTEGRATING SYSTEMS
18. vladikk doit-intl.com #ndcsydney { “type”: “presentation-started”, “timestamp”: 1556969773, “createdBy”: 12, “payload” : { … } }
19. vladikk doit-intl.com #ndcsydney TYPES OF EVENTS Event Notification Event-Carried State Transfer Event Sourcing / Domain Event
20. vladikk doit-intl.com #ndcsydney EVENT NOTIFICATION Something important No (direct) response Minimal informaAon
21. vladikk doit-intl.com #ndcsydney EVENT NOTIFICATION
22. vladikk doit-intl.com #ndcsydney TYPES OF EVENTS Event Notification Event-Carried State Transfer Event Sourcing / Domain Event
23. vladikk doit-intl.com #ndcsydney { “customerId”: “123”, “name”: “John Johnson”, “state”: “approved”, … }
24. vladikk doit-intl.com #ndcsydney TYPES OF EVENTS Event Notification Event-Carried State Transfer Event Sourcing / Domain Event
25. vladikk doit-intl.com #ndcsydney EVENT SOURCING / DOMAIN EVENTS Events are the source of truth CombinaAon of noAficaAon and state transfer “Immutable, stateless, truthful”
26. vladikk doit-intl.com #ndcsydney EVENT SOURCING / DOMAIN EVENTS
27. vladikk doit-intl.com #ndcsydney TYPES OF EVENTS Notification Event:
 { “type”: “Marriage”, … }
 Event-Carried State Transfer { “type”: “PersonalDetailsChanged”, “newLastName”: “johnson” } Domain Event: { “type”: “GotMarried”, “partnerId”: “TZ7138821”, “assumedPartnersLastName”: true }
28. vladikk doit-intl.com #ndcsydney STORIES OF WAR AND HORROR
29. vladikk doit-intl.com #ndcsydney
30. vladikk doit-intl.com #ndcsydney FROM MONOLITH TO MICROLITHS 01
31. vladikk doit-intl.com #ndcsydney Monolith Everything
32. vladikk doit-intl.com #ndcsydney Marketing CRM BI Clients Notification Event
33. vladikk doit-intl.com #ndcsydney Marketing CRM BI Clients Notification Event Calculate Metrics
34. vladikk doit-intl.com #ndcsydney Marketing CRM BI Clients Notification Event Calculate Metrics Logical Coupling
35. vladikk doit-intl.com #ndcsydney Marketing CRM BI Clients Notification Event Calculate Metrics Logical Coupling Transactional Coupling
36. vladikk doit-intl.com #ndcsydney Marketing CRM BI Clients Domain Event Event Sourcing
37. vladikk doit-intl.com #ndcsydney Marketing CRM BI Clients Domain Event Event Sourcing
38. vladikk doit-intl.com #ndcsydney COMMANDS MASQUERADING AS EVENTS 02
39. vladikk doit-intl.com #ndcsydney CRM Relational Database Marketing BI Clients State
40. vladikk doit-intl.com #ndcsydney CRM Event Store Sales Agent Relational Database CRM Result Command
41. vladikk doit-intl.com #ndcsydney CRM Event Store Sales Agent Execution Result Command Projections
42. vladikk doit-intl.com #ndcsydney COUPLED PROJECTIONS 03
43. vladikk doit-intl.com #ndcsydney Event Store Domain Events BI Search Indexes Materialized Views (UI) State Projections
44. vladikk doit-intl.com #ndcsydney Event Store Domain Events BI Search Indexes Materialized Views (UI) Duplicated Logic Logical Coupling
45. vladikk doit-intl.com #ndcsydney Event Store Many Types of Events!!! BI Search Indexes Materialized Views (UI) Duplicated Logic Logical Coupling Implementation Coupling
46. vladikk doit-intl.com #ndcsydney Event Store State Change Notification BI Search Indexes Materialized Views (UI) Private Events Service Boundary State Projection
47. vladikk doit-intl.com #ndcsydney ARCHITECTURAL TROJAN HORSE 04
48. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D
49. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D New
 Microservice
50. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D Implementation Coupling
51. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D Anti-Corruption Layer New
 Microservice Model Transformation Business Complexity
52. vladikk doit-intl.com #ndcsydney DISTRIBUTED MONOLITH 05
53. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D
54. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D
55. vladikk doit-intl.com #ndcsydney Microservice A Microservice B Microservice C Microservice D
56. vladikk doit-intl.com #ndcsydney OPTIMISTIC CONSISTENCY 06
57. vladikk doit-intl.com #ndcsydney System DB User Message Bus Backup DB Cached State Analysis Model Enriched From
58. vladikk doit-intl.com #ndcsydney System DB User Message Bus Same “Transaction” Backup DB Cached State Analysis Model Enriched From Transactional Coupling
59. vladikk doit-intl.com #ndcsydney System DB User Message Bus Same “Transaction” Backup DB Cached State Analysis Model Enriched From Transactional Coupling Transactional Coupling
60. vladikk doit-intl.com #ndcsydney System DB User Message Bus Same “Transaction” Backup DB Cached State Analysis Model Enriched From Transactional Coupling Transactional Coupling Temporal Coupling
61. vladikk doit-intl.com #ndcsydney System DB Message Bus Backup DB Cached State Analysis Model OUTBOX PATTERN
62. vladikk doit-intl.com #ndcsydney LESSONS LEARNED
63. vladikk doit-intl.com #ndcsydney BE PESSIMISTIC
64. vladikk doit-intl.com #ndcsydney BE PESSIMISTIC System DB Backup DB Analysis Model Cached State
65. vladikk doit-intl.com #ndcsydney BE PESSIMISTIC Assume that everything will fail Event-Driven Architecture - The “driven” part is there for a reason Ensure delivery of events no matter what
66. vladikk doit-intl.com #ndcsydney PRIVATE / PUBLIC EVENTS Event Store BI Search Indexes Materialized Views (UI) State Projection
67. vladikk doit-intl.com #ndcsydney PRIVATE / PUBLIC EVENTS Private events - Implementation details. Public events - Public API. Should be stable. Use public events to “compress” private events.
68. vladikk doit-intl.com #ndcsydney EVALUATE SERVICES’ CONSISTENCY REQUIREMENTS Eventual consistency? - Event-Carried State Transfer Read last write? - Notification Event + API for getting up-to-date data Concurrency control? - Merge them ASAP!
69. vladikk doit-intl.com #ndcsydney EVALUATE SERVICES’ CONSISTENCY REQUIREMENTS Eventual consistency? - Event-Carried State Transfer Read last write? - Notification Event + API for getting up-to-date data Concurrency control? - Merge them ASAP!
70. vladikk doit-intl.com #ndcsydney Be pessimistic Use private and public events Evaluate consistency requirements LESSONS LEARNED
71. vladikk doit-intl.com #ndcsydney WRAP UP
72. vladikk doit-intl.com #ndcsydney Manages complexity Local complexity - complexity of a system’s component Global complexity - interconnectedness between components SOFTWARE ARCHITECTURE
73. vladikk doit-intl.com #ndcsydney Notification Event - something interesting happened Event-Carried State Transfer - publishing changes in data Domain Events - immutable, truthful, stateless TYPES OF EVENTS
74. vladikk doit-intl.com #ndcsydney Be pessimistic Use private and public events Evaluate consistency requirements LESSONS LEARNED
75. https://bit.ly/2ptJ5fS THANK YOU! @vladikk vladikk.com https://bit.ly/31nSD9c http://careers.doit-intl.com