flowable/flowable-engine · error · FlowableException

failed to send event

Error message

failed to send event

What it means

When the Kafka producer future completes exceptionally with an ExecutionException whose cause is not a RuntimeException, the adapter wraps that cause in FlowableException("failed to send event"). This is the generic path for broker-side or serialization failures during a synchronous outbound event send.

Solutions

1. Inspect e.getCause() (attached to this FlowableException) for the real Kafka failure.
2. Verify broker connectivity, bootstrap servers and topic existence.
3. Check Kafka client security config (SASL/SSL) and max.request.size.
4. Wrap or retry sends with a dead-letter policy for persistent failures.

Example fix

null

// pre-check broker connectivity
try (AdminClient admin = AdminClient.create(Map.of("bootstrap.servers", servers))) {
    admin.describeCluster().nodes().get(5, TimeUnit.SECONDS);
}

try {
    outboundEventBus.send(event);
} catch (FlowableException e) {
    if ("failed to send event".equals(e.getMessage()) && isTransient(e.getCause())) {
        retryWithBackoff(event);
    } else { deadLetter(event, e.getCause()); }
}

When it happens

Trigger: kafkaOperations.send(...).get() throws ExecutionException caused by a checked/non-Runtime Throwable, e.g. TimeoutException, authentication/authorization errors (SaslAuthenticationException, TopicAuthorizationException), or serialization errors surfaced as non-Runtime exceptions.

Common situations: Kafka broker down or unreachable (timeout), wrong SASL credentials, topic missing with auto-create disabled, oversized message exceeding max.request.size.

Understand the failure class

Background: "API request failed": what wrapped HTTP errors from external APIs mean and how to find the real cause — this error's family across 29 libraries.

Related errors

• At least one of topics, topicPartitions or topicPattern…
• Channel definition cannot resolve as a String[] or a String
• Channel model in tenant has retry configuration but no…
• Could not resolve the KafkaListenerContainerFactory to use…
• Endpoint registry does not have listenerContainers field

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/b923df032804fbb1. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-event-registry-spring/src/main/java/org/flowable/eventregistry/spring/kafka/KafkaOperationsOutboundEventChannelAdapter.java:78

                if (headerValue != null) {
                    headers.add(new RecordHeader(headerKey, headerValue.toString().getBytes(StandardCharsets.UTF_8)));
                }
            }

            Integer partition = partitionProvider == null ? null : partitionProvider.determinePartition(event);
            Object key = messageKeyProvider == null ? null : messageKeyProvider.determineMessageKey(event);

            ProducerRecord<Object, Object> producerRecord = new ProducerRecord<>(topic, partition, key, rawEvent, headers);
            kafkaOperations.send(producerRecord).get();
            
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new FlowableException("Sending the event was interrupted", e);
        } catch (ExecutionException e) {
            if (e.getCause() instanceof RuntimeException) {
                throw (RuntimeException) e.getCause();
            } else {
                throw new FlowableException("failed to send event", e.getCause());
            }
        }
    }

    @Override
    public void sendEvent(Object rawEvent, Map<String, Object> headerMap) {
        throw new UnsupportedOperationException("Outbound processor should never call this");
    }
}

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