Can a Producer send a key with a message?

• A. Yes
• B. No
• C. Only in certain configurations
• D. Not applicable

Answer: (A)

A message can carry a key in Kafka. When you create a record, you can supply both a key and a value; the producer sends them together to the broker. The key is serialized and used by the partitioner to choose which partition the record goes to—by default, the key is hashed to pick a partition, so all records with the same key end up in the same partition. That enables per-key ordering within that partition. The key is optional, so you can send a message with a key or with a null key, depending on whether you want keyed partitioning. So, sending a key with a message is supported and commonly used.