Is absolute message delivery guaranteed in Kafka, and how is it achieved?

Kafka does not guarantee exactly-once delivery of messages out of the box, but it provides at-least-once delivery.

To achieve stricter guarantees, the following mechanisms are used:

• Idempotent producers: prevent duplicate messages during retries.
• Transactions: allow grouping of produce operations and offset commits, ensuring atomicity.
• Offset control on the consumer side: allows precise tracking of processed messages.

Thus, with idempotent producers and transactions, it is possible to approach exactly-once semantics, but an absolute guarantee depends on proper configuration and handling on the application side.