Slides from my talk at GOTOpia November 2020 about the right balance between choreography (event-driven communication) and orchestration (command-driven communication)

1. Balancing
Choreography &
Orchestration
@berndruecker

2. Choreography is great!
Photo by Lijian Zhang, under Creative Commons SA 2.0 License

3. What we wanted
Photo by Lijian Zhang, under Creative Commons SA 2.0 License and Wikimedia Commons / CC BY-SA 4.0
@berndruecker

4. Opinions…
https://stackoverflow.com/questions/4127241/orchestration-vs-choreography

7. Idon‘tagree!

9. Example
Checkout
Payment
Inventory
Shipment
@berndruecker

10. Synchronous
call chains
„Synchronous call
chains are evil!“
added latency, low availability,
resource utilization, …

11. An asynchronous
call chain

12. Choreography or Orchestration?

15. Choreography or Orchestration?

16. Order
Placed
Payment
Received
Goods
Fetched
Notification
Event-driven
@berndruecker
Checkout
Payment
Inventory
Shipment

17. Peer-to-peer event chains
Checkout
Payment
Inventory
Shipment
Order
placed
Payment
received
Goods
shipped
Goods
fetched
@berndruecker

18. Phil Calcado at QCon NYC 2019

19. Notification
Checkout
Payment
Inventory
Shipment
@berndruecker
Pinball Machine Architecture
„What the hell just happened?“
@berndruecker

20. Peer-to-peer event chains
Checkout
Payment
Inventory
Shipment
Order
placed
Payment
received
Goods
shipped
Goods
fetched
@berndruecker

21. Why is it so tempting?
Service
A
Event Bus
A
B
Service
B
C
Service
C
D
E
F
Service
D
G
Service
…
Service
…
Service …
Service
…
Service …
Service …
Service
…
@berndruecker

22. Why is it so tempting?
Service
A
Event Bus
A
B
Service
B
C
Service
C
D
E
F
Service
D
G
Service
…
Service
…
Service …
Service
…
Service …
Service …
Service
…
Adding is easy!
You can „buy“ a shorter
initial time-to-value
by choreography.
It yields in technical debt.
@berndruecker

23. Peer-to-peer event chains
Checkout
Payment
Inventory
Shipment
Order
placed
Payment
received
Goods
shipped
Goods
fetched
Fetch the goods
before the
payment
@berndruecker

24. Peer-to-peer event chains
Checkout
Payment
Inventory
Shipment
Fetch the goods
before the
payment
Goods
fetched
Order
placed
Payment
received
Goods
shipped
@berndruecker

25. Order
Decide about responsibility
Checkout
Payment
Inventory
ShipmentPayment
received
Order
placed
Retrieve
payment
@berndruecker
This is
choreography
This is
orchestration

26. My definition
Orchestration = command-driven communication
Choreography = event-driven communication

27. Order
Decide about responsibility
Checkout
Payment
Inventory
Shipment
Order
placed
Retrieve
payment
It can still be messaging!
@berndruecker

28. Order
Checkout
Payment
Inventory
Shipment
Stateful orchestration
This orchestration
requires state
@berndruecker

29. Warning:
Contains Opinion
@berndruecker

30. mail@berndruecker.io
@berndruecker
http://berndruecker.io/
Bernd Ruecker
Co-founder and
Chief Technologist of
Camunda

31. Order
Checkout
Payment
Inventory
Shipment
@berndruecker

32. Glue code (e.g. Java)
https://github.com/berndruecker/flowing-
retail/blob/master/kafka/java/order-
zeebe/src/main/java/io/flowing/retail/kafka/or
der/flow/FetchGoodsAdapter.java

33. Using a workflow engine
Workflow Engine
Scheduler
Durable State
Glue Code Whatever you
need…
Workflow Definition
Workflow Engine:
Is stateful
Can wait
Can retry
Can escalate
Can compensate
Provides visibility

34. Now it is easy to change the process flow
@berndruecker

35. Processes are domain logic and live inside service boundaries
@berndruecker

36. Challenge:
Command vs. Event
Event
Command
vs

37. ?
Event Command
Message Record Event
Fact,
happened in the past,
immutable
Intend,
Want s.th. to happen,
The intention itself is a fact

38. ?
Event Command
Message Record Event

39. Commands in disguise
The Customer Needs To Be
Sent A Message To Confirm
Address Change
Event
Send
Message
Wording of
Sender
Wording of
recipient

40. Checkout Order Payment
Event-driven:
Decision to couple is on the receiving side
Command-driven
Decision to couple is on the sending side
Direction of dependency
Retrieve
Payment
Order
placed
Payment
received
Direction of dependency

41. Distributed Monoliths
Authorization
Service
Document Context Page
Context
Document
attached
Page
created
Document
moved
Page
moved
…

42. Define stable contract/API instead
Authorization
Service
Document Context Page
Context
Add
auth
…

43. Who is responsible?

44. Order
Order
Notification
Notification
Payment
Send
legal docs
Payment
received
Order
placed
Send
email
It is all about responsibility!

45. Customer Created
Sam Newman: Building Microservices

46. Customer Onboarding is a mix!
Orchestration
Orchestration
Orchestration
Choreography

47. Your ITarchitecture
Choreography
Orchestration
@berndruecker
Your services
or applications

48. Monolith Chaos
Choreography
Orchestration
@berndruecker
Your services
or applications

49. Your ITarchitecture
Monolith Chaos
Choreography
Orchestration
Your services
or applications
Balance choreography and orchestration
@berndruecker

50. # Orchestration != central
# Choreography != decoupled
# Orchestration = Command-driven
# Choreography = Event-driven
# You need to balance both!
# It is mostly about responsibility and the direction of coupling
@berndruecker

51. Want to learn more?
https://learning.oreilly.com/get-learning/?code=PPAER20

52. Thank you!
@berndruecker

53. mail@berndruecker.io
@berndruecker
https://berndruecker.io
https://medium.com/berndruecker
https://github.com/berndruecker
https://www.infoq.com/articles/events-
workflow-automation
Contact:
Slides:
Blog:
Code:
https://www.infoworld.com/article/3254777/
application-development/
3-common-pitfalls-of-microservices-
integrationand-how-to-avoid-them.html
https://thenewstack.io/5-workflow-automation-
use-cases-you-might-not-have-considered/