Complex Event Flows in Distributed Systems (Bernd Ruecker, Camunda) Kafka Summit NYC 2019
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The document discusses common hypotheses regarding event-driven architecture in distributed systems, emphasizing that events can decrease coupling, orchestration should be avoided, and workflow engines can be cumbersome. It warns against the complexity introduced by making systems decoupled through event notification without understanding the larger flow and stresses the importance of choosing the right tools and methodologies. Lightweight workflow engines are suggested as useful alternatives that can alleviate developer challenges and improve visibility in business processes.
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") //
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
What do I mean by
„lightweight?“
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-52-320.jpg)
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") //
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
Build engine
in one line of
code
(using in-
memory H2)
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-53-320.jpg)
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow")
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
Define flow
e.g. in Java
DSL
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-54-320.jpg)
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow")
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
Define flow
e.g. in Java
DSL
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-55-320.jpg)
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow")
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
We can attach
code…
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-57-320.jpg)
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow")
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
…that is
called when
workflow
instances pass
through
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-58-320.jpg)
![public static void main(String[] args) {
ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration()
.buildProcessEngine();
engine.getRepositoryService().createDeployment() //
.addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow")
.startEvent()
.serviceTask("Step1").camundaClass(SysoutDelegate.class)
.serviceTask("Step2").camundaClass(SysoutDelegate.class)
.endEvent()
.done()
).deploy();
engine.getRuntimeService().startProcessInstanceByKey(
"flow", Variables.putValue("city", "New York"));
}
public class SysoutDelegate implements JavaDelegate {
public void execute(DelegateExecution execution) throws Exception {
System.out.println("Hello " + execution.getVariable("city"));
}
}
Start
instances
@berndruecker](https://image.slidesharecdn.com/berndrueckercamundacomplexeventflowsindistributedsystemsfinal4-190405164250/85/Complex-Event-Flows-in-Distributed-Systems-Bernd-Ruecker-Camunda-Kafka-Summit-NYC-2019-59-320.jpg)
Complex Event Flows in Distributed Systems (Bernd Ruecker, Camunda) Kafka Summit NYC 2019
- 1. Complex event flows in distributed systems @berndruecker
- 2. 3 common hypotheses I check today: # Events decrease coupling # Orchestration needs to be avoided # Workflow engines are painful @berndruecker
- 4. Berlin, Germany [email protected] @berndruecker Bernd Ruecker Co-founder and Chief Technologist of Camunda
- 6. Simplified example: dash button Photo by 0xF2, available under Creative Commons BY-ND 2.0 license. https://www.flickr.com/photos/0xf2/29873149904/ @berndruecker
- 9. Autonomous (micro-)services Checkout Payment Inventory Shipment Dedicated Application Processes Dedicated infrastructure Dedicated Development Teams @berndruecker
- 11. Example Checkout Payment Inventory Shipment The button blinks if we can ship within 24 hours @berndruecker
- 12. Request/response: temporal coupling Checkout Payment Inventory Shipment Request Response The button blinks if we can ship within 24 hours @berndruecker
- 13. Temporal decoupling with events and read models Checkout Payment Inventory Shipment Good Stored Read Model Good Fetched The button blinks if we can ship within 24 hours *Events are facts about what happened (in the past) @berndruecker
- 15. Events can decrease coupling* *e.g. decentral data-management, read models, extract cross-cutting aspects @berndruecker
- 18. 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 @berndruecker
- 19. 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 @berndruecker
- 20. 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 @berndruecker
- 21. Monitoring Workflows Across Microservices https://www.infoq.com/articles/monitor-workflow-collaborating-microservices @berndruecker
- 22. Typical approachesDistributed Tracing Data Lake / Event Monitoring Process Mining Process Tracking @berndruecker
- 23. Stefan Tilkov: Microservice Patterns & Antipatterns - MicroXchg 2018 @berndruecker
- 24. Peer-to-peer event chains Checkout Payment Inventory Shipment Order placed Payment received Goods shipped Goods fetched Fetch the goods before the payment @berndruecker
- 25. Peer-to-peer event chains Checkout Payment Inventory Shipment Fetch the goods before the payment Goods fetched Order placed Payment received Goods shipped @berndruecker
- 26. Photo by born1945, available under Creative Commons BY 2.0 license. @berndruecker
- 27. What we wanted Photo by Lijian Zhang, available under Creative Commons SA 2.0 License and Pedobear19 / CC BY-SA 4.0 @berndruecker
- 28. „Challenges?“ Source: Microservices orchestration survey, July 2018, 354 responses https://camunda.com/microservices-orchestration-survey-results-2018/ @berndruecker
- 29. Order Extract the end-to-end responsibility Checkout Payment Inventory Shipment *Commands have an intent about what needs to happen in the future Payment received Order placed Retrieve payment @berndruecker
- 30. Order It is about where to decide about the coupling! Checkout Payment Inventory Shipment Order placed Retrieve payment Order decides . to listen to the event . to issue the command @berndruecker
- 31. Order It is about where to decide about the coupling! Checkout Payment Inventory Shipment Order placed Retrieve payment It can still be messaging! @berndruecker
- 32. Commands help to avoid (complex) peer-to-peer event chains @berndruecker
- 33. Orchestration needs to be avoided @berndruecker
- 35. Dumb pipes Checkout Payment Inventory Shipment Order Smart endpoints and dumb pipes Martin Fowler @berndruecker
- 36. Danger of god services? Checkout Order A few smart god services tell anemic CRUD services what to do Sam Newmann Payment Inventory Shipment @berndruecker
- 37. Danger of god services? Checkout Payment Inventory Shipment Order A few smart god services tell anemic CRUD services what to do Sam Newmann @berndruecker
- 38. A god service is only created by bad API design! @berndruecker
- 42. Example Order Payment If the credit card was rejected, the customer can provide new details Credit Card Retrieve Payment Rejected Rejected @berndruecker
- 43. Example Order Payment Client of dumb endpoints easily become a god services. If the credit card was rejected, the customer can provide new details Credit Card Retrieve Payment Rejected Rejected @berndruecker
- 44. Payment failed Who is responsible to deal with problems? Order Payment If the credit card was rejected, the customer can provide new details Credit Card Retrieve Payment Rejected Payment received @berndruecker
- 45. Payment failed Long running services Order Payment Credit Card Retrieve Payment Rejected Payment received Smart endpoints are potentially long-running @berndruecker
- 46. Persist thing (Entity, Actor, …) State machine or workflow engine Typical concerns DIY = effort, accidental complexity Scheduling, Versioning, operating, visibility, scalability, … Handling State @berndruecker
- 47. Workflow engines are painful Complex, proprietary, heavyweight, central, developer adverse, … @berndruecker
- 48. Avoid the wrong tools! Death by properties panel Low-code is great! (You can get rid of your developers!) Complex, proprietary, heavyweight, central, developer adverse, … @berndruecker
- 49. Workflow engines, state machines It is relevant in modern architectures @berndruecker
- 50. CADENCE Silicon valley has recognized Workflow engines, state machines @berndruecker
- 52. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") // .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } What do I mean by „lightweight?“ @berndruecker
- 53. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") // .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } Build engine in one line of code (using in- memory H2) @berndruecker
- 54. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } Define flow e.g. in Java DSL @berndruecker
- 55. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } Define flow e.g. in Java DSL @berndruecker
- 56. BPMN Business Process Model and Notation ISO Standard @berndruecker
- 57. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } We can attach code… @berndruecker
- 58. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } …that is called when workflow instances pass through @berndruecker
- 59. public static void main(String[] args) { ProcessEngine engine = new StandaloneInMemProcessEngineConfiguration() .buildProcessEngine(); engine.getRepositoryService().createDeployment() // .addModelInstance("flow.bpmn", Bpmn.createExecutableProcess("flow") .startEvent() .serviceTask("Step1").camundaClass(SysoutDelegate.class) .serviceTask("Step2").camundaClass(SysoutDelegate.class) .endEvent() .done() ).deploy(); engine.getRuntimeService().startProcessInstanceByKey( "flow", Variables.putValue("city", "New York")); } public class SysoutDelegate implements JavaDelegate { public void execute(DelegateExecution execution) throws Exception { System.out.println("Hello " + execution.getVariable("city")); } } Start instances @berndruecker
- 60. Payment Now you have a state machine! @berndruecker Workflow Engine
- 61. Payment Easy to handle time @berndruecker
- 63. Example with synchronous communication REST Order Payment Credit Card @berndruecker
- 64. Example with synchronous communication REST Order Payment Credit Card @berndruecker
- 65. Example with synchronous communication REST Order Payment Credit Card @berndruecker
- 66. Example with synchronous communication REST Order Payment Credit Card Stateful Retry @berndruecker
- 67. Works also for asynchronous communication Order Payment Credit Card Monitor Timeouts @berndruecker
- 68. Anything wrong with this?
- 69. Anything wrong with this?
- 70. Distributed systems introduce complexity you have to tackle! Credit Card Payment The service can be long running. You get a better API and fewer gods @berndruecker
- 71. Workflows live inside service boundaries @berndruecker Workflow Engine Workflow
- 75. Homework: Try to do this purely event-driven! Send to: [email protected] @berndruecker
- 76. Biz Dev Leverage state machine & workflow engine Living documentation Visibility in testing improve communication improve communication Ops @berndruecker
- 77. Visual HTML reports for test cases @berndruecker
- 78. Living documentation for long-running behaviour @berndruecker
- 80. Biz Dev Leverage state machine & workflow engine Living documentation Visibility in testing Operate with visibility and context Understand and discuss business processes Evaluate optimizations in-sync with implementation improve communication improve communication Ops @berndruecker
- 81. Monitoring Workflows Across Microservices https://www.infoq.com/articles/monitor-workflow-collaborating-microservices @berndruecker
- 82. Tracking Checkout Inventory Payment Shipment Event Bus Workflow Engine https://www.confluent.io/kafka-summit-sf18/the_big_picture @berndruecker Kafka Connect
- 83. Journey towards more orchestration @berndruecker
- 84. Vodafone, Liongate & WDW Presented at CamundaCOn Berlin 2018
- 85. Before mapping processes explicitly with BPMN, the truth was buried in the code and nobody knew what was going on. Jimmy Floyd, 24 Hour Fitnesse „ @berndruecker
- 86. … It addresses one of the core issues in a distributed microservices architecture—where is the source of truth for the coordinated interaction of the entire system? … the system we are replacing uses a complex peer- to-peer choreography that requires reasoning across multiple codebases to understand. https://medium.com/@sitapati/node-js-client-for-zeebe-microservices-orchestration-engine-72287e4c7d94 Josh Wulf Credit Sense @berndruecker
- 87. Lightweight workflow engines are great – don‘t DIY* *e.g. enabling potentially long-running services, solving hard developer problems, can run decentralized @berndruecker
- 89. Event-driven example: Choreography & Tracking InventoryPayment ShippingCheckout Tracking https://github.com/berndruecker/flowing-retail/ H2 @berndruecker
- 90. Event-driven example: Choreography + Orchestration InventoryPaymentOrder ShippingCheckout Monitor https://github.com/berndruecker/flowing-retail/ H2 H2 @berndruecker
- 91. # Events decrease coupling: sometimes read-models, but no complex peer-to-peer event chains! # Orchestration needs to be avoided: sometimes no ESB, smart endpoints/dumb pipes, balance orchestration and choreography # 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 @berndruecker