Zeebe exporter class cast exception

[Michal_Stefaniuk]

Hey guys, I’m working on a custom zeebe exporter. I had some issues with it before

Cannot register custom exporter

Hey guys, I was just playing around with zeebe exporters, I’m trying to register it in zeebe and somehow I’m getting this weirds error. Here is what I done: 1. Implemented a simple zeebe exporter Right now for testing purposes it’s very simple public class DemoExporter implements Exporter { Controller controller; public void open(Controller controller) { this.controller = controller; } public void export(Record record) { System.out.println(record.toJson()); …

Now my exporter has become a part of a multi module gradle project (I migrated it to maven) and unfortunately on zeebe startup I get this exception

java.lang.IllegalStateException: Failed to execute CommandLineRunner
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:774) [spring-boot-3.1.2.jar:3.1.2]
        at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:755) [spring-boot-3.1.2.jar:3.1.2]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:319) [spring-boot-3.1.2.jar:3.1.2]
        at io.camunda.zeebe.broker.StandaloneBroker.main(StandaloneBroker.java:82) [camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
Caused by: java.lang.IllegalStateException: Failed to load exporter with configuration: ExporterCfg{, jarPath='/usr/local/zeebe/lib/zeebe-exporter-demo-1.0-SNAPSHOT-jar-with-dependencies.jar', className='io.zeebe.exporters.Demo.DemoExporter', args={logLevel=debug, prettyPrint=false}}
        at io.camunda.zeebe.broker.Broker.buildExporterRepository(Broker.java:149) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:70) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:49) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.StandaloneBroker.run(StandaloneBroker.java:91) ~[camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-3.1.2.jar:3.1.2]
        ... 3 more
Caused by: io.camunda.zeebe.broker.exporter.repo.ExporterLoadException: Cannot load exporter [demoexporter]: cannot load specified class
        at io.camunda.zeebe.broker.exporter.repo.ExporterRepository.load(ExporterRepository.java:82) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.buildExporterRepository(Broker.java:147) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:70) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:49) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.StandaloneBroker.run(StandaloneBroker.java:91) ~[camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-3.1.2.jar:3.1.2]
        ... 3 more
Caused by: java.lang.ClassCastException: class io.zeebe.exporters.Demo.DemoExporter
        at java.lang.Class.asSubclass(Unknown Source) ~[?:?]
        at io.camunda.zeebe.broker.exporter.repo.ExporterRepository.load(ExporterRepository.java:80) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.buildExporterRepository(Broker.java:147) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:70) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.Broker.<init>(Broker.java:49) ~[zeebe-broker-8.3.0-alpha4.jar:8.3.0-alpha4]
        at io.camunda.zeebe.broker.StandaloneBroker.run(StandaloneBroker.java:91) ~[camunda-zeebe-8.3.0-alpha4.jar:8.3.0-alpha4]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-3.1.2.jar:3.1.2]
        ... 3 more

Any thoughts on this one? I’m still building and deploying with java 11 so I hope it’s not a big deal (since Zeebe requires jdk+17). With maven and as a separate module it worked perfectly fine for me.

I was able to trace it in the zeebe codebase that there is a problem with exporter registartion and this is the line throwing exception:

try {
  final Class<?> specifiedClass = classLoader.loadClass(config.getClassName());
  --> exporterClass = specifiedClass.asSubclass(Exporter.class); <---
} catch (final ClassNotFoundException | ClassCastException e) {
  throw new ExporterLoadException(id, "cannot load specified class", e);
}

But I’m almost running out of ideas so any help is appreciated. Thanks.

[lenaschoenburg]

Hey Michal

Just a guess as the stack trace really doesn’t give away much: Is your exporter compiled with the same version of Zeebe that you are trying to run it with?
I think if your dependency on Zeebe is for example 8.2.12 but you are deploying it to a Zeebe broker in version 8.2.13, you’d get a ClassCastException.

[adrianAzoitei]

@lenaschoenburg

tack trace really doesn’t give away much: Is your exporter compiled with the same version of Zeebe that you are trying to run it with?

Did you manage to move past this? Running into the same now with Zeebe 8.5.0. Tried compiling the exporter to both jdk 17 and 21, with no success.

[deepCamunda]

I am facing the same issue too. did you guys figure out a way forward?

[deepCamunda]

I was able to resolve my errors, posting in case someone else faces the same:
the subclass error is a generic error. for me the underneath cause was that I had tenant index custom configuration, and index name has to be in all smallcase.

[Ale_K]

Can you check that you don’t have the class:

io/camunda/zeebe/exporter/api/Exporter.class

in your generated jar?

Use:
jar -tf your-exporter-jar-with-dependencies.jar | grep Exporter

If you have it, then exclude the class or the whole io.camunda:zeebe-exporter-api package from the assembly

[sinugaud]

Can you go through this ,
Version might be deprecated, but procedure is same

Zeebe Exporters

Exporters allow you to tap into the Zeebe event stream on a partition and export selected events to other systems. You can filter events, perform transformations, and even trigger side-effects from an exporter.

Read a two-part series about building Zeebe exporters on the Zeebe blog: Part One | Part Two.

Important Things to Know About Exporters

1. Resource Impact:

   • Exporters run in the same JVM as the broker.
   • Intensive computation in an exporter impacts broker throughput.
   • Perform minimal processing in the exporter and handle further transformations in another system.

2. Disk Management:

   • A misbehaving exporter can cause broker disks to fill up.
   • The event log truncates only up to the earliest exporter position.
   • Ensure exporters advance their positions in the stream to prevent disk issues.

3. Failure Planning:

   • Design for connectivity failures with external systems.

---

Building an Exporter

Create a Maven Project

mvn archetype:generate -DgroupId=io.zeebe \
    -DartifactId=zeebe-exporter-demo \
    -DarchetypeArtifactId=maven-archetype-quickstart  \
    -DinteractiveMode=false

Add Dependency

Update pom.xml:

<dependencies>
    <dependency>
        <groupId>io.camunda</groupId>
        <artifactId>zeebe-exporter-api</artifactId>
        <version>8.5.0</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
</dependencies>

Rename and Modify File

1. Rename src/main/java/io.zeebe/App.java to DemoExporter.java.
2. Edit DemoExporter.java to implement the Exporter interface:

import io.camunda.zeebe.exporter.api.Exporter;
import io.camunda.zeebe.exporter.api.context.Context;
import io.camunda.zeebe.exporter.api.context.Controller;
import io.camunda.zeebe.protocol.record.Record;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class DemoExporter implements Exporter {
    private static final Logger log = LoggerFactory.getLogger(DemoExporter.class);
    private Controller controller;

    @Override
    public void configure(Context context) {
    }

    @Override
    public void open(Controller controller) {
        log.info("Exporter Open");
        this.controller = controller;
    }

    @Override
    public void close() {
    }

    @Override
    public void export(Record record) {
        log.info("Hello from exporter");
        log.info("--- Zeebe record : {} ---", record.toString());
        this.controller.updateLastExportedRecordPosition(record.getPosition());
    }
}

---

Exporter Lifecycle

1. configure

• Allows the exporter to read configuration from the zeebe.cfg.toml file.
• If an error occurs, the broker halts.

2. open

• Provides a reference to the Controller for marking records as exported.

3. close

• Used for cleanup during broker shutdown.

4. export

• Called when a record is available for export.
• Marks the record as exported.

---

Deploy Exporters to Zeebe

Build Exporter

Run the command:

mvn package

Update Zeebe Configuration

1. Move the generated .jar file (without dependencies) to the Zeebe location.
2. Update the Zeebe configuration file:

exporters:
  incident:
    className: io.zeebe.camunda.exporter.incident.DemoExporter
    jarPath: /exporters/zeebe-exporter-demo-1.0-SNAPSHOT.jar

Broker Configuration Example

zeebe:
  broker:
    gateway:
      enable: true
      network:
        port: 26500
      security:
        enabled: false

    network:
      host: 0.0.0.0

    data:
      directory: data
      logSegmentSize: 128MB
      snapshotPeriod: 15m

    cluster:
      clusterSize: 1
      replicationFactor: 1
      partitionsCount: 1

    threads:
      cpuThreadCount: 2
      ioThreadCount: 2

    exporters:
      incident:
        className: io.zeebe.camunda.exporter.incident.DemoExporter
        jarPath: /exporters/zeebe-exporter-demo-1.0-SNAPSHOT.jar

---

Verify Logs

Check broker logs for exporter messages:

2024-09-05 13:16:18.970 [Broker-0] [zb-fs-workers-0] [Exporter-1] INFO
  io.zeebe.camunda.exporter.incident.DemoExporter - Exporter Open
2024-09-05 13:16:18.981 [Broker-0] [zb-fs-workers-0] [Exporter-1] INFO
  io.zeebe.camunda.exporter.incident.DemoExporter - Hello from exporter
2024-09-05 13:16:18.983 [Broker-0] [zb-fs-workers-0] [Exporter-1] INFO
  io.zeebe.camunda.exporter.incident.DemoExporter - --- Zeebe record : {...}