[jira] [Created] (KAFKA-7412) Bug prone response from producer.send(ProducerRecord, Callback) if Kafka broker is not running

["Michal Turek (JIRA)" <ji...@apache.org>]

Michal Turek created KAFKA-7412:
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             Summary: Bug prone response from producer.send(ProducerRecord, Callback) if Kafka broker is not running
                 Key: KAFKA-7412
                 URL: https://issues.apache.org/jira/browse/KAFKA-7412
             Project: Kafka
          Issue Type: Bug
          Components: producer 
    Affects Versions: 2.0.0
            Reporter: Michal Turek
         Attachments: metadata_when_kafka_is_stopped.png

Hi there, I have probably found a bug in Java Kafka producer client.

Scenario & current behavior:
- Start Kafka broker, single instance.
- Start application that produces messages to Kafka.
- Let the application to load partitions for a topic to warm up the producer, e.g. send a message to Kafka. I'm not sure if this is necessary step, but our code does it.
- Gracefully stop the Kafka broker.
- Application logs now contains "org.apache.kafka.clients.NetworkClient: [Producer clientId=...] Connection to node 0 could not be established. Broker may not be available." so the client is aware about the Kafka unavailability.
- Trigger the producer to send a message using KafkaProducer.send(ProducerRecord, Callback) method.
- The callback that notifies business code receives non-null RecordMetadata and null Exception after request.timeout.ms. The metadata contains offset -1 which is value of ProduceResponse.INVALID_OFFSET.

Expected behavior:
- If the Kafka is not running and the message is not appended to the log, the callback should contain null RecordMetadata and non-null Exception. At least I subjectively understand the Javadoc this way, "exception on production error" in simple words.
- Developer that is not aware of this behavior and that doesn't test for offset -1, may consider the message as successfully send and properly acked by the broker.

Known workaround
- Together with checking for non-null exception in the callback, add another condition for ProduceResponse.INVALID_OFFSET.

Used setup
- Latest Kafka 2.0.0 for both broker and Java client.
- Originally found with broker 0.11.0.1 and client 2.0.0.
- Code is analogy of the one in Javadoc of KafkaProducer.send().
- Used producer configuration (others use defaults).

{noformat}
    bootstrap.servers = "localhost:9092"
    client.id = "..."
    acks = "all"
    retries = 1
    linger.ms = "20"
    compression.type = "lz4"
    request.timeout.ms = 5000 # The same behavior is with default, this is to speed up the tests
{noformat}



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