A business rule task is used to model the evaluation of a business rule; for example, a decision modeled in Decision Model and Notation (DMN).
The differences between these task types are the visual representation (i.e. the task marker) and the semantics for the model.
When a process instance enters a business rule task, it creates a corresponding job and waits for its completion. A job worker should request jobs of this job type and process them. When the job is completed, the process instance continues.
Jobs for business rule tasks are not processed by Zeebe itself. To process them, you must provide a job worker.
Defining a task
A business rule task must define a job type the same way as a service task does. This specifies the type of job workers should subscribe to (e.g. DMN).
Use task headers to pass static parameters to the job worker (e.g. the key of the decision to evaluate).
Take a look at the Zeebe DMN Worker. This is a community extension providing a job worker to evaluate DMN decisions. You can run it, or use it as a blueprint for your own job worker.
A business rule task with a custom header:
<bpmn:businessRuleTask id="calculate-risk" name="Calculate risk">
<zeebe:taskDefinition type="DMN" />
<zeebe:header key="decisionRef" value="risk" />