Between which elements do Kafka delivery guarantees work?

Delivery guarantees in Apache Kafka operate between the producer, broker, and consumer. The main types of guarantees:

• At most once — a message may be delivered 0 or 1 times, without retries, possible data loss.
• At least once — a message is delivered at least once, duplicates may occur.
• Exactly once — a message is delivered exactly once, with no loss or duplication.

These guarantees are ensured through interactions:

• Between the producer and broker: write acknowledgments (acks), retries.
• Between the broker and consumer: offset control, processing acknowledgments.

For example, the exactly-once semantics use an idempotent producer and transactions to guarantee atomicity of message writing and processing.