* A:Kafka batches storecompression metadata in their headers, indicating how the batch was compressed.
* B:Compression is controlled via theproducer config compression.type, which defaults to none.
Producers explicitly set Gzip or other formats.
FromKafka Producer Docs:
"Compression is done by the producer, and the type is stored in the message batch metadata. The broker does not recompress."
* C is false: messages are serializedbeforecompression.
* D is false: messages without keys are distributed acrossmultiple partitions.
Reference:Kafka Producer Configs > compression.type

ForSASL/PLAIN authentication over SSL, the correct combination is:
* security.protocol=SASL_SSL
* sasl.jaas.config=...PlainLoginModule required username=... password=...
FromKafka Security Documentation:
"For SASL/PLAIN over SSL, configure security.protocol=SASL_SSL and provide login module configuration using sasl.jaas.config." Options B and D are incorrect because they do not pair the correct protocol with the authentication method.
Reference:Apache Kafka Security Configs > SASL_SSL, PLAIN mechanism

In Kafka Streams, the application.id is also the underlying group.id for your consumers, and the prefix for all internal topics (repartition and state)

session.timeout.ms must be decreased to 3 seconds to allow for a faster rebalance, and the heartbeat thread must be quicker, so we also need to decrease heartbeat.interval.ms

The onCompletion() method of Kafka'sCallback interfaceis executedonce the broker acknowledgesthe message. This includes success or failure, and it isinvoked asynchronouslyby the producer.
FromKafka Java Client API Documentation:
"The onCompletion method will be called when the record sent to the server has been acknowledged, or when an error occurs." This ensures thatthe record was sent and acknowledged, not just added to a batch or local buffer.
Reference:Kafka Java Client API > org.apache.kafka.clients.producer.Callback