Delivery semantics for consumers

- Consuemers choose when to commit offsets.

- There are 3 delivery sematics:

- At most once:

    - offsets are committed as soon as the message is received.

    - If the processing goes wrong, the message will be lost(it won't be read again).

- At least once(usually preferred):

    - offsets are committed after the message is processed.

    - If the processing goes wrong, the message will be read again.

    - This can result in duplicate processing of messages. Make sure your processing is idempotent (i.e. processing again the messages won't impact your systems)

- Exactly once:

    - Can be achieved for Kafka => Kafka workflows using Kafka Streams API

    - For Kafka => External System workflows, use an idempotent consumer.