Error Handling

Kafka Streams applications must handle various error types gracefully. This guide covers exception handling strategies, dead letter queues, and recovery patterns.

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Error Types

Error Type	Location	Cause
Deserialization	Input	Invalid message format
Processing	Topology	Application logic failure
Production	Output	Broker unavailable, serialization error
Uncaught	Anywhere	Unhandled exception

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Deserialization Errors

Default Behavior

By default, deserialization errors cause the stream to fail:

// Throws exception on bad message
KStream<String, Order> orders = builder.stream("orders");
// If any message fails to deserialize, stream thread dies

LogAndContinue Handler

Skip bad records and continue processing:

props.put(
    StreamsConfig.DEFAULT_DESERIALIZATION_EXCEPTION_HANDLER_CLASS_CONFIG,
    LogAndContinueExceptionHandler.class
);

LogAndFail Handler (Default)

Fail the stream on deserialization error:

props.put(
    StreamsConfig.DEFAULT_DESERIALIZATION_EXCEPTION_HANDLER_CLASS_CONFIG,
    LogAndFailExceptionHandler.class
);

Custom Handler

Implement custom logic for deserialization errors:

public class CustomDeserializationHandler implements DeserializationExceptionHandler {
    private final Producer<byte[], byte[]> dlqProducer;

    @Override
    public DeserializationHandlerResponse handle(ProcessorContext context,
                                                  ConsumerRecord<byte[], byte[]> record,
                                                  Exception exception) {
        // Log the error
        log.error("Deserialization failed for record at offset {} in {}-{}",
            record.offset(), record.topic(), record.partition(), exception);

        // Send to dead letter queue
        ProducerRecord<byte[], byte[]> dlqRecord = new ProducerRecord<>(
            record.topic() + ".dlq",
            record.key(),
            record.value()
        );
        dlqRecord.headers()
            .add("error.message", exception.getMessage().getBytes())
            .add("error.offset", Long.toString(record.offset()).getBytes());

        dlqProducer.send(dlqRecord);

        // Continue processing
        return DeserializationHandlerResponse.CONTINUE;
    }

    @Override
    public void configure(Map<String, ?> configs) {
        // Initialize DLQ producer
        dlqProducer = new KafkaProducer<>(configs);
    }
}

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Production Errors

Default Handler

props.put(
    StreamsConfig.DEFAULT_PRODUCTION_EXCEPTION_HANDLER_CLASS_CONFIG,
    DefaultProductionExceptionHandler.class  // Fails on error
);

Custom Production Handler

public class CustomProductionHandler implements ProductionExceptionHandler {

    @Override
    public ProductionExceptionHandlerResponse handle(ProducerRecord<byte[], byte[]> record,
                                                     Exception exception) {
        if (exception instanceof RecordTooLargeException) {
            // Skip oversized records
            log.warn("Record too large, skipping: {}", record.key());
            return ProductionExceptionHandlerResponse.CONTINUE;
        }

        if (isRetriable(exception)) {
            // Retry transient errors
            log.warn("Retriable production error, will retry: {}", exception.getMessage());
            return ProductionExceptionHandlerResponse.CONTINUE;
        }

        // Fail on non-retriable errors
        log.error("Non-retriable production error: {}", exception.getMessage());
        return ProductionExceptionHandlerResponse.FAIL;
    }

    private boolean isRetriable(Exception e) {
        return e instanceof TimeoutException ||
               e instanceof NotLeaderOrFollowerException;
    }
}

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Processing Errors

Try-Catch in Processors

stream.mapValues(value -> {
    try {
        return processValue(value);
    } catch (ProcessingException e) {
        log.error("Processing failed: {}", e.getMessage());
        return null;  // Or return error marker
    }
})
.filter((key, value) -> value != null);  // Filter out failures

Branch Pattern for Error Handling

// Split stream into success and failure branches
Map<String, KStream<String, ProcessingResult>> branches = stream
    .mapValues(value -> {
        try {
            return ProcessingResult.success(process(value));
        } catch (Exception e) {
            return ProcessingResult.failure(value, e);
        }
    })
    .split(Named.as("processing-"))
    .branch((key, result) -> result.isSuccess(), Branched.as("success"))
    .branch((key, result) -> !result.isSuccess(), Branched.as("failure"))
    .noDefaultBranch();

// Process successful records
branches.get("processing-success")
    .mapValues(ProcessingResult::getValue)
    .to("output");

// Send failures to DLQ
branches.get("processing-failure")
    .mapValues(ProcessingResult::toErrorRecord)
    .to("errors");

Dead Letter Queue Pattern

public class DlqProcessor implements Processor<String, Event, String, Event> {
    private ProcessorContext<String, Event> context;
    private final String dlqTopic;

    @Override
    public void process(Record<String, Event> record) {
        try {
            Event processed = processEvent(record.value());
            context.forward(record.withValue(processed));
        } catch (Exception e) {
            // Send to DLQ
            sendToDlq(record, e);
        }
    }

    private void sendToDlq(Record<String, Event> record, Exception e) {
        Record<String, Event> dlqRecord = record.withHeaders(
            record.headers()
                .add("error.message", e.getMessage().getBytes())
                .add("error.timestamp", Long.toString(System.currentTimeMillis()).getBytes())
                .add("error.class", e.getClass().getName().getBytes())
        );

        // Forward to DLQ sink
        context.forward(dlqRecord, "dlq-sink");
    }
}

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Uncaught Exception Handler

Handle any exception that escapes the topology:

streams.setUncaughtExceptionHandler(exception -> {
    log.error("Uncaught exception in stream thread", exception);

    // Analyze exception type
    if (exception instanceof RetriableException) {
        // Replace the thread and continue
        return StreamsUncaughtExceptionHandler.StreamThreadExceptionResponse.REPLACE_THREAD;
    }

    if (exception instanceof FatalException) {
        // Shutdown the entire application
        return StreamsUncaughtExceptionHandler.StreamThreadExceptionResponse.SHUTDOWN_APPLICATION;
    }

    // Default: shutdown just this client
    return StreamsUncaughtExceptionHandler.StreamThreadExceptionResponse.SHUTDOWN_CLIENT;
});

Exception Response Options

Response	Behavior
REPLACE_THREAD	Replace failed thread, continue processing
SHUTDOWN_CLIENT	Shutdown this Streams instance
SHUTDOWN_APPLICATION	Shutdown all instances via protocol

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State Restoration Errors

// Handle state restoration failures
streams.setStateRestoreListener(new StateRestoreListener() {
    @Override
    public void onRestoreStart(TopicPartition partition, String storeName,
                               long startOffset, long endOffset) {
        log.info("Starting restoration of {} from {} to {}",
            storeName, startOffset, endOffset);
    }

    @Override
    public void onBatchRestored(TopicPartition partition, String storeName,
                                long batchEndOffset, long numRestored) {
        // Track progress
    }

    @Override
    public void onRestoreEnd(TopicPartition partition, String storeName, long totalRestored) {
        log.info("Completed restoration of {}: {} records", storeName, totalRestored);
    }
});

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Retry Patterns

Simple Retry with Backoff

public class RetryingProcessor implements Processor<String, Event, String, Event> {
    private static final int MAX_RETRIES = 3;
    private static final long INITIAL_BACKOFF_MS = 100;

    @Override
    public void process(Record<String, Event> record) {
        int attempt = 0;
        long backoff = INITIAL_BACKOFF_MS;

        while (attempt < MAX_RETRIES) {
            try {
                Event result = processEvent(record.value());
                context.forward(record.withValue(result));
                return;
            } catch (RetriableException e) {
                attempt++;
                if (attempt < MAX_RETRIES) {
                    log.warn("Attempt {} failed, retrying in {}ms", attempt, backoff);
                    sleep(backoff);
                    backoff *= 2;
                }
            }
        }

        // Max retries exceeded
        sendToDlq(record, new MaxRetriesExceededException());
    }
}

External Service Circuit Breaker

public class CircuitBreakerProcessor implements Processor<String, Event, String, Event> {
    private final CircuitBreaker circuitBreaker;
    private ProcessorContext<String, Event> context;

    @Override
    public void process(Record<String, Event> record) {
        try {
            Event result = circuitBreaker.executeSupplier(() -> callExternalService(record.value()));
            context.forward(record.withValue(result));
        } catch (CallNotPermittedException e) {
            // Circuit is open - send to retry topic
            context.forward(record, "retry-sink");
        } catch (Exception e) {
            // Other failures - send to DLQ
            sendToDlq(record, e);
        }
    }
}

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Error Monitoring

Metrics

Key metrics to monitor:

Metric	Description	Alert Threshold
skipped-records-rate	Records skipped due to errors	> 0.1%
failed-stream-threads	Stream threads that failed	> 0
rebalance-rate	Rebalance frequency	> 1/hour
process-latency	Processing time	> SLA

Custom Error Metrics

public class MetricsProcessor implements Processor<String, Event, String, Event> {
    private final Counter successCounter;
    private final Counter errorCounter;
    private final Counter dlqCounter;

    @Override
    public void init(ProcessorContext<String, Event> context) {
        this.context = context;

        // Register metrics
        StreamsMetrics metrics = context.metrics();
        successCounter = metrics.addSensor("processing-success");
        errorCounter = metrics.addSensor("processing-error");
        dlqCounter = metrics.addSensor("dlq-sent");
    }

    @Override
    public void process(Record<String, Event> record) {
        try {
            Event result = processEvent(record.value());
            context.forward(record.withValue(result));
            successCounter.increment();
        } catch (Exception e) {
            errorCounter.increment();
            sendToDlq(record, e);
            dlqCounter.increment();
        }
    }
}

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Recovery Patterns

Graceful Shutdown

Runtime.getRuntime().addShutdownHook(new Thread(() -> {
    log.info("Shutting down streams application");
    streams.close(Duration.ofSeconds(30));
}));

State Recovery

// Configure for faster recovery
props.put(StreamsConfig.NUM_STANDBY_REPLICAS_CONFIG, 1);

// Monitor state
streams.setStateListener((newState, oldState) -> {
    log.info("State changed from {} to {}", oldState, newState);

    if (newState == KafkaStreams.State.ERROR) {
        // Alert and potentially restart
        alertOps("Streams application entered ERROR state");
    }
});

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Best Practices

Error Handling Strategy

Practice	Recommendation
Define error types	Classify retriable vs fatal
Use DLQ	Never lose data
Log context	Include offset, key, error details
Monitor errors	Alert on error rate thresholds

Configuration

Practice	Recommendation
Set appropriate handlers	Custom handlers for production
Configure retries	retries, retry.backoff.ms
Enable standby replicas	Faster recovery
Set processing guarantees	Match business requirements

Testing

Practice	Recommendation
Test error paths	Inject failures in tests
Verify DLQ flow	Ensure errors reach DLQ
Test recovery	Verify state restoration
Load test errors	Ensure error handling scales

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Related Documentation

• Kafka Streams Overview - Stream processing concepts
• DSL Reference - Stream operations
• State Stores - State management
• Consumer Error Handling - Consumer patterns