Slides from my talk at JCon live on 21st of November 2023. Code examples are here: https://github.com/berndruecker/flowing-retail/

1. @berndruecker
Live coding some
(microservice)
integration patterns

2. Photo by Tookapic, available under Creative Commons CC0 1.0 license.

3. „There was an error
while sending your
boarding pass“

4. Check-in
Web-UI
Me
Current situation

5. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Current situation

6. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Current situation

7. Some
Service
Some
Service
Some
Service
Some
Service
Some
Service
Some
Service
Some
Service
Failure will happen.
Accept it!
But keep it local!
Be resilient.

8. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Current situation – the bad part

9. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Current situation – the bad part

10. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Current situation – the bad part
Stateful
Retry

12. We are having some technical
difficulties and cannot present you
your boarding pass right away.
But we do actively retry ourselves, so
lean back, relax and we will send it
on time.

13. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Possible situation – much better!

14. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Possible situation – much better!
Stateful
Retry

15. Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
Stateful
Retry
Possible situation – much better!
The failure
never leaves
this scope!

16. Resulting challenges
Persistent state Asynchronous
communication
We will talk about why this is
a good thing in a minute!
Solve technical challenges
(operating, scheduling,
versioning, visibility,
scalability, …) without
accidential complexity
Change the user experience

17. Warning:
Contains Opinion

18. bernd.ruecker@camunda.com
@berndruecker
http://berndruecker.io/
Bernd Ruecker
Co-founder and
Chief Technologist of
Camunda

19. Check-In
A workflow engine is a durable state machine
Barcode
REST
Stateful
retry

20. „The customer wants a synchronous response“
Check-in
Barcode
Generator
Web-UI
Me
Output
Mgmt
„Eh – no!“

21. Simple example for live coding
Credit
Card
Payment
REST

22. Live hacking
https://github.com/berndruecker/flowing-retail

23. Payment
Now you have a state machine!
Credit
Card
REST

24. Do you have to program
all integration
logic?
26

26. @berndruecker

27. Connectors Modeling
Experience
Low-code
Forms
Human Task
Orchestration
CAMUNDA
Low-code Pro-code
Process Orchestration
Kopfhörer

28. @berndruecker

29. @OutboundConnector(
type = "io.camunda:http-json:1", inputVariables = {"method", ...},
)
public class HttpJsonFunction implements OutboundConnectorFunction {
public Object execute(final OutboundConnectorContext context) throws Exception {
final var json =;
final var request = createRequest(context);
return httpService.executeConnectorRequest(request);
}
} {
"name": "REST Connector",
"properties": [
{
"type": "Hidden",
"value": "io.camunda:http-json:1",
"binding": {
"type": "zeebe:taskDefinition:type"
}
},
{
"id": "method",
"label": "REST Method",
"group": "endpoint",
"type": "Dropdown",
"value": "get",
"choices": [
https://github.com/camunda/connectors-bundle/tree/main/connectors/http-json

30. @berndruecker

31. Runs anywhere
Multiple connector runtime options,
including SaaS, self-managed, co-
located, and local installations
@berndruecker

35. Criticality,
value,
complexity…
Use Cases
@berndruecker

36. or
enable
@berndruecker

37. Criticality,
value,
complexity…
Use Cases
@berndruecker

38. Payment
But back to integration logic…
Credit
Card
REST

39. has to implement
Retry
has to implement
Idempotency
Client Service Provider

40. Make every service idempotent!
Credit
Card
Payment
Charge Credit Card
cardNumber
amount
Charge Credit Card
cardNumber
amount
transactionId
Not idempotent
Idempotent
charge

43. Don‘t worry, it will happen safely –
even if you loose connection.
Feel free to reload this page any time!

44. Distributed systems introduce complexity you have to tackle!
Credit
Card
Payment
REST

45. Distributed
systems

46. It is impossible to
differentiate certain
failure scenarios.
Independant of
communication style!
Service
Provider
Client

47. Distributed systems introduce complexity you have to tackle!
Credit
Card
Payment
REST

48. Distributed systems introduce complexity you have to tackle!
Credit
Card
Payment
REST
Cancel
charge

49. retrievePayment
HTTP 200 OK
HTTP 202 ACCEPTED
Payment
Happy case: Synchronous response
Otherwise: asynchronous
Embrace asynchronicity

50. Live hacking
https://github.com/berndruecker/flowing-retail/blob/master/rest/java/payment/
src/main/java/io/flowing/retail/payment/rest/PaymentRestHacksControllerV4.java

51. Long running capabilities
are essential to design
good service boundaries
(= a good architecture)
@berndruecker

52. Example
Order
Fulfillment
Payment
Retrieve
Payment
@berndruecker

53. Example
Order
Fulfillment
Payment
Credit
Card
Retrieve
Payment
@berndruecker

54. Example
Order
Fulfillment
Payment
Credit
Card
Retrieve
Payment
Rejected
@berndruecker

55. Example
Order
Fulfillment
Payment
If the credit
card was
rejected, the
customer can
provide new
details
Credit
Card
Retrieve
Payment
Rejected
Rejected
@berndruecker

56. Example
Order
Fulfillment
Payment
If the credit
card was
rejected, the
customer can
provide new
details
Credit
Card
Retrieve
Payment
Rejected
Rejected
@berndruecker
A few
smart god services
tell
anemic CRUD services
what to do
Sam Newmann

57. Payment
failed
Who is responsible to deal with problems?
Order
Fulfillment
Payment
If the credit
card was
rejected, the
customer can
provide new
details
Credit
Card
Retrieve
Payment
Rejected
Payment
received
@berndruecker

58. Payment
failed
(Potentially) long running services
Order
Fulfillment
Payment
Credit
Card
Retrieve
Payment
Rejected
Payment
received
@berndruecker

59. Long running capabilities
are essential to design
good service boundaries
(= a good architecture)
@berndruecker

60. You need to redesign
your customer journeys
to leverage your
hipster architecture!
Shutterstock

61. Did you just say “hipster”?

62. Let‘s talk about messaging.

63. Who uses a message bus?

64. Who has no problems
operating a message bus?
Dead messages | No context | Inaccesible payload | Hard to redeliver |
Home-grown message hospitals | …

65. Using messaging
Credit
Card
Request
Dead letter queue
(DLQ)

66. Using messaging
Credit
Card
Request
Dead letter queue
(DLQ)

67. Manigfold architecture options
https://blog.bernd-ruecker.com/architecture-options-to-run-a-workflow-engine-6c2419902d91

68. Manigfold architecture options
https://blog.bernd-ruecker.com/architecture-options-to-run-a-workflow-engine-6c2419902d91

69. Manigfold architecture options
https://blog.bernd-ruecker.com/architecture-options-to-run-a-workflow-engine-6c2419902d91

70. Did you just say “hipster”?

71. Order
Placed
Payment
Received
Goods
Shipped
Notification
Event-driven & Reactive
@berndruecker
Checkout
Payment
Inventory
Shipment

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

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

74. Phil Calcado at QCon NYC 2019

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

76. What we wanted
Photo by Lijian Zhang, available under Creative Commons SA 2.0 License and Pedobear19 / CC BY-SA 4.0

77. The danger is that it's very easy to make
nicely decoupled systems with event
notification, without realizing that you're
losing sight of that larger-scale flow, and
thus set yourself up for trouble in future
years.
https://martinfowler.com/articles/201701-event-driven.html

78. The danger is that it's very easy to make
nicely decoupled systems with event
notification, without realizing that you're
losing sight of that larger-scale flow, and
thus set yourself up for trouble in future
years.
https://martinfowler.com/articles/201701-event-driven.html

79. The danger is that it's very easy to make
nicely decoupled systems with event
notification, without realizing that you're
losing sight of that larger-scale flow, and
thus set yourself up for trouble in future
years.
https://martinfowler.com/articles/201701-event-driven.html

80. Extract Orchestration logic

81. Orchestration logic live inside service boundaries

82. Event-driven example
Inventory
Payment
Order Shipping
Checkout Monitor
https://github.com/berndruecker/flowing-retail/
Human
Tasks
H2 H2

83. Code
https://github.com/berndruecker/flowing-retail

84. Summary

85. Thank you!