How to handle kafka publishing failure in robust way

Question

I'm using Kafka and we have a use case to build a fault tolerant system where not even a single message should be missed. So here's the problem: If publishing to Kafka fails due to any reason (ZooKeeper down, Kafka broker down etc) how can we robustly handle those messages and replay them once things are back up again. Again as I say we cannot afford even a single message failure. Another use case is we also need to know at any given point in time how many messages were failed to publish to Kafka due to any reason i.e. something like counter functionality and now those messages needs to be re-published again.

One of the solution is to push those messages to some database (like Cassandra where writes are very fast but we also need counter functionality and I guess Cassandra counter functionality is not that great and we don't want to use that.) which can handle that kind of load and also provide us with the counter facility which is very accurate.

This question is more from architecture perspective and then which technology to use to make that happen.

PS: We handle some where like 3000TPS. So when system start failing those failed messages can grow very fast in very short time. We're using java based frameworks.

Thanks for your help!

Answer 1

The reason Kafka was built in a distributed, fault-tolerant way is to handle problems exactly like yours, multiple failures of core components should avoid service interruptions. To avoid a down Zookeeper, deploy at least 3 instances of Zookeepers (if this is in AWS, deploy them across availability zones). To avoid broker failures, deploy multiple brokers, and ensure you're specifying multiple brokers in your producer bootstrap.servers property. To ensure that the Kafka cluster has written your message in a durable manor, ensure that the acks=all property is set in the producer. This will acknowledge a client write when all in-sync replicas acknowledge reception of the message (at the expense of throughput). You can also set queuing limits to ensure that if writes to the broker start backing up you can catch an exception and handle it and possibly retry.

Using Cassandra (another well thought out distributed, fault tolerant system) to "stage" your writes doesn't seem like it adds any reliability to your architecture, but does increase the complexity, plus Cassandra wasn't written to be a message queue for a message queue, I would avoid this.

Properly configured, Kafka should be available to handle all your message writes and provide suitable guarantees.

Answer 2

I am super late to the party. But I see something missing in above answers :)

The strategy of choosing some distributed system like Cassandra is a decent idea. Once the Kafka is up and normal, you can retry all the messages that were written into this.

I would like to answer on the part of "knowing how many messages failed to publish at a given time"

From the tags, I see that you are using apache-kafka and kafka-consumer-api.You can write a custom call back for your producer and this call back can tell you if the message has failed or successfully published. On failure, log the meta data for the message.

Now, you can use log analyzing tools to analyze your failures. One such decent tool is Splunk.

Below is a small code snippet than can explain better about the call back I was talking about:

public class ProduceToKafka {

  private ProducerRecord<String, String> message = null;

 // TracerBulletProducer class has producer properties
  private KafkaProducer<String, String> myProducer = TracerBulletProducer
      .createProducer();

  public void publishMessage(String string) {

    ProducerRecord<String, String> message = new ProducerRecord<>(
        "topicName", string);

    myProducer.send(message, new MyCallback(message.key(), message.value()));
  }

  class MyCallback implements Callback {

    private final String key;
    private final String value;

    public MyCallback(String key, String value) {
      this.key = key;
      this.value = value;
    }


    @Override
    public void onCompletion(RecordMetadata metadata, Exception exception) {
      if (exception == null) {
        log.info("--------> All good !!");
      } else {
        log.info("--------> not so good  !!");
        log.info(metadata.toString());
        log.info("" + metadata.serializedValueSize());
        log.info(exception.getMessage());

      }
    }
  }

}

If you analyze the number of "--------> not so good !!" logs per time unit, you can get the required insights.

God speed !

Answer 3

Chris already told about how to keep the system fault tolerant.

Kafka by default supports at-least once message delivery semantics, it means when it try to send a message something happens, it will try to resend it.

When you create a Kafka Producer properties, you can configure this by setting retries option more than 0.

 Properties props = new Properties();
 props.put("bootstrap.servers", "localhost:4242");
 props.put("acks", "all");
 props.put("retries", 0);
 props.put("batch.size", 16384);
 props.put("linger.ms", 1);
 props.put("buffer.memory", 33554432);
 props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
 props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

 Producer<String, String> producer = new KafkaProducer<>(props);

For more info check this.