How to check to see if Ruby-Kafka retries works? - ruby-on-rails

Question

In the documentation it is mentioned that producer retries to send the message to the queue based on max_retries.
So I shutdown the Kafka and then tried my producer. I get this error
Fetching cluster metadata from kafka://localhost:9092
[topic_metadata] Opening connection to localhost:9092 with client id MYCLIENTID
ERROR -- : [topic_metadata] Failed to connect to localhost:9092: Connection refused
DEBUG -- : Closing socket to localhost:9092
ERROR -- : Failed to fetch metadata from kafka://localhost:9092
Completed 500 Internal Server Error in 486ms (ActiveRecord: 33.9ms)
which it make sense, however the retries never happens after that. I have read the doc inside-out and I can't figure it out how this retries actually going to trigger?
Here is my code:
def self.deliver_message(kafka, message, topic, transactional_id)
producer = kafka.producer(idempotent: true,
transactional_id: transactional_id,
required_acks: :all,
max_retries: 5,
retry_backoff: 5)
producer.produce(message, topic: topic)
producer.deliver_messages
end
link to doc:
https://www.rubydoc.info/gems/ruby-kafka/Kafka/Producer#initialize-instance_method
Thank you in advance.

Answer 1

The retries are based on the type of Exception thrown by the producer callback. According to the Callback Docs there are the following Exception possible happening during callback:
The exception thrown during processing of this record. Null if no error occurred. Possible thrown exceptions include:
Non-Retriable exceptions (fatal, the message will never be sent):
InvalidTopicException
OffsetMetadataTooLargeException
RecordBatchTooLargeException
RecordTooLargeException
UnknownServerException
Retriable exceptions (transient, may be covered by increasing #.retries):
CorruptRecordException
InchvalidMetadataException
NotEnoughReplicasAfterAppendException
NotEnoughReplicasException
OffsetOutOfRangeException
TimeoutException
UnknownTopicOrPartitionException
Shutting down Kafka completely rather looks like a non-retriable Exception.