Greetings to Camunda, Zeebe and Dapr!

It’s awesome to see how Dapr and Camunda workflow engine work well together. By using BPMN and DMN we completely remove business logic from the code and only expose APIs to bind calls from Dapr Zeebe binding. The project can be found on GitHub.

Story - the business process

Expecting a sad person having difficulties learning a new language and it would make her happier if someone greets her. But depending on her learning skills (Score Person Learning Curve) she may desire the greeting or not. If her score is more than 30% she receives greeting by email. If less, it generates a business error and sends email to administrator. Yes, cruel world.

BPMN Workflow

Decide how to greet

Example

Since Dapr does all the hard work, we’re left with only few tasks to do. See the full solution on GitHub.

Run infrastructure docker compose to start

Using Camunda Modeler upload BPMN workflow to Camunda self-hosted instance

Have a config file to bind MQTT topic…

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: greeting-request
  namespace: greetings-camunda
spec:
  type: bindings.mqtt
  version: v1
  metadata:
  - name: url
    value: mqtt://host.docker.internal:1883
  - name: topic
    value: camunda/greeting-requested
  - name: consumerID
    value: "{uuid}"
  scopes:
    - greetings-api

Have an API controller with endpoint…

/// <summary>
/// Receiving a message to MQTT pubsub and topic named "camunda/greeting-requested" 
/// and it should start a new Camunda Greet process by invoking zeebe-command binding.
/// </summary>
[HttpPost("/greeting-request")]
public async Task<ActionResult> GreetingRequested([FromBody, Required] GreetingRequest request, [FromServices] DaprClient daprClient)
{
    logger.LogInformation(request.ToString());

    // serialize and deserialize request to get it into dictionary format.
    var json = JsonConvert.SerializeObject(request, jsonSerializerSettings);

    // start Camunda process by invoking a message to Camunda
    await daprClient.InvokeBindingAsync<PublishMessageRequest, PublishMessageResponse>(Bindings.ZeebeCommand, Commands.PublishMessage,
        new PublishMessageRequest("greeting-requested", request.GreetingId.ToString(), string.Concat("decide-greeting-", request.GreetingId), "10s", // TTL
        JsonConvert.DeserializeObject<Dictionary<string, string>>(json)));

    return Ok();
}

Build & start APIs

docker compose up -d --build

Run simulation from sim folder

dotnet run 10

Zeebe binding triggers a new process in BPMN workflow in Camunda

Issues

Throwing business error does not send the ErrorMessage to Camunda engine or at least it’s not accessible in “Send email to admin” task. Hence setting the property explicitly - feels a bit awkward to me.

Whatever I define in Input field is a string. Even though I’d expect it’s Time as on. Then using it in DMN diagram is impossible (or don’t know how) as it always ends with error comparing ValString and ValTime.

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