3/06/2022

Learning Camunda/Zeebe by Example - SAGA Pattern

 






























Purpose of this blogpost is to explain how to use Zeebe/Camunda to implement SAGA pattern with Microservices.

This is the next episode of previous blogpost

To setup Zeebe cluster in Kubernetes, you have to follow same steps in previous blogpost.

Also I have made a slight different to docker-compose.yml files, to run it in host network.
Please refer this git commit for for details : 


Now let's build the project with maven command : mvn clean install

https://github.com/dhanuka84/SAGA-Microservices-Zeebe/tree/main/src/zeebe-saga-spring-boot





Then Build the docker images with maven spring-boot plugin:

mvn spring-boot:build-image


  • To deploy Zeebe cluster, you have to go through same steps given in previous post.

Deploy MongoDB Cluster

MONGO_REPLICASET_HOST=mongo docker-compose -f src/zeebe-saga-spring-boot/docker/docker-compose-mongo.yaml up



Deploy Microservices

docker-compose  -f src/zeebe-saga-spring-boot/docker/docker-compose-micros.yaml up



Test Microservices Health with Actuator ( status, liveness, readiness)



dhanuka@dhanuka:~$ curl http://localhost:8081/actuator/health | jq '. | {status: .status, liveness: .components.livenessState.status, readiness: .components.readinessState.status,}'   


  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

100   352  100   352    0     0    592      0 --:--:-- --:--:-- --:--:--   593

{

  "status": "UP",

  "liveness": "UP",

  "readiness": "UP"

}


dhanuka@dhanuka:~$ curl http://localhost:8083/actuator/health | jq '. | {status: .status, liveness: .components.livenessState.status, readiness: .components.readinessState.status,}'   


  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

100   352  100   352    0     0    824      0 --:--:-- --:--:-- --:--:--   822

{

  "status": "UP",

  "liveness": "UP",

  "readiness": "UP"

}


dhanuka@dhanuka:~$ curl http://localhost:8084/actuator/health | jq '. | {status: .status, liveness: .components.livenessState.status, readiness: .components.readinessState.status,}'   


  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

100   352  100   352    0     0    675      0 --:--:-- --:--:-- --:--:--   675

{

  "status": "UP",

  "liveness": "UP",

  "readiness": "UP"

}




dhanuka@dhanuka:~$ curl http://localhost:8082/actuator/health | jq '. | {status: .status, liveness: .components.livenessState.status, readiness: .components.readinessState.status,}'   


  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

100   352  100   352    0     0    820      0 --:--:-- --:--:-- --:--:--   822

{

  "status": "UP",

  "liveness": "UP",

  "readiness": "UP"

}



Deploy Zeebe BPMN Process


dhanuka@dhanuka:~$ zbctl deploy workflows/saga-example.bpmn --insecure

{

  "key": "2251799813703663",

  "processes": [

    {

      "bpmnProcessId": "trip-booking",

      "version": 1,

      "processDefinitionKey": "2251799813703662",

      "resourceName": "workflows/saga-example.bpmn"

    }

  ]

}



Create a booking via Rest Call to Booking Microservice

 

dhanuka@dhanuka:~$ curl --location --request POST 'http://localhost:8081/booking/' \

--header 'Content-Type: application/json' \

--data-raw '{

    "id" : "0",

    "clientId":"123",

    "resourceId":"987",

    "fromDate":"2021-02-22T14:52:44.494264+01:00",

    "toDate":"2021-03-06T14:52:44.495451+01:00",

    "createdAt":"2021-02-10T14:52:44.495469+01:00",

    "active":false

}'

 

{"id":"0","clientId":"123","houseBookingId":"642c957b-f7ed-45d9-8719-b11fa451dbfa","carBookingId":"dbb44830-2cb6-4c02-ab5d-bf0850e69bb0","flightBookingId":"b573f7ca-cab9-48ab-9bdf-cc08e5e199ae","fromDate":"2021-02-22T13:52:44.494264Z","toDate":"2021-03-06T13:52:44.495451Z","createdAt":"2021-02-10T13:52:44.495469Z","active":false}

  •  Once you login to Zeebe dashboard via http://localhost:8080/ , you can select the process id (trip-booking) and then version, then you can select the process instance
  • Then you can see the happy path of the work flow.

 

 
Java Code Explanation
 

1. Where is Zeebee Process Instance Created?

https://github.com/dhanuka84/SAGA-Microservices-Zeebe/blob/main/src/zeebe-saga-spring-boot/booking-microservice/src/main/java/com/example/booking/service/impl/BookingServiceImpl.java

 

 

  • As you can see, the instance was created in line 34.

Key Points:

  1. Line 34 : Spring WebFlux, which provides reactive programming support for web applications

https://www.baeldung.com/spring-webflux

  1. Line 37: Creating a variable called bookingResult with Booking data.

  2. Line 40: Usage of Completable Futures.

https://www.callicoder.com/java-8-completablefuture-tutorial/#:~:text=Future%20vs%20CompletableFuture,result%20of%20an%20asynchronous%20computation.

  1. Line 49: Save the Trip Booking entity when received hotel booking id, car booking id and flight booking id.

  2. So all the operations within and outside the microservice will be asynchronous and reactive.

 

2. Zeebee Task polling/requesting for jobs, then execute and response back to broker.

  • Let’s take Hotel Booking as an example.

https://github.com/dhanuka84/SAGA-Microservices-Zeebe/blob/main/src/zeebe-saga-spring-boot/hotel-microservice/src/main/java/com/example/hotel/task/BookingTask.java

 

 

 

Key Points:

  1. Line 41,42,43 : Access job data. 

  2. Line 45 : Validate the job based on headers

  3. Line 50: Access Booking Info, based on requestName (bookingResult) variable value, which was created when process instance creation.

  4. Line 64: Create Hotel Booking and reactively update Zeebe with response.

  • Note that now the resultName variable value of response is bookHotelResult.

Failure Path Testing

  • You have to change the BPMN configuration to enable simulateError as below.


 

Deploy workflow process next version 

dhanuka@dhanuka:~$ zbctl deploy workflows/saga-example.bpmn --insecure

{

  "key": "2251799813703663",

  "processes": [

    {

      "bpmnProcessId": "trip-booking",

      "version": 2,

      "processDefinitionKey": "2251799813703662",

      "resourceName": "workflows/saga-example.bpmn"

    }

  ]

}

 

Create a booking via Rest Call to Booking Microservice

 

dhanuka@dhanuka:~$ curl --location --request POST 'http://localhost:8081/booking/' \

--header 'Content-Type: application/json' \

--data-raw '{

    "id" : "0",

    "clientId":"123",

    "resourceId":"987",

    "fromDate":"2021-02-22T14:52:44.494264+01:00",

    "toDate":"2021-03-06T14:52:44.495451+01:00",

    "createdAt":"2021-02-10T14:52:44.495469+01:00",

    "active":false

}'

 

  • Now you can see the failure path of the workflow 
  • We failed the work flow from Flight Booking task.
  • The failure will be propagated to other tasks which is polling on same instance_id .




Failure Path Java Explanation 


Key Points


1. We have a separate Zeebe task (ex: flight-booking-rollback) to handle failure scenario. This task simply delete relevant booking.

2. Line 45: If the SimulateError true, then this will trigger Failed response to Zeebe.





3. Now according tho BPMN workflow , if BookingFlight Result is not success, then it will call ServiceTask_CancelFlight as target reference.


 

As you can see ServiceTask_CancelFlight task definition is flight-booking-rollback .










Because of this, there will be a job to execute for flight-booking-rollback  task in Java Class.

4. Now how come this propagate to other Microservices?




In the BPMN configuration , you can see the chain of call from ServiceTask_CancelFlight to ServiceTask_CancelCar and ServiceTask_CancelHotel.

This will helped to create rollback jobs for other Microservices rollback tasks.



Some inspirational videos :)





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