What guarantees of delivery have you encountered in Kafka, what are they, and which ones have you worked with?

Apache Kafka has three main message delivery guarantees:

1. At most once — a message may be delivered 0 or 1 times. Loss of messages is possible, but duplicates will not occur.

2. At least once — a message is guaranteed to be delivered, but may be delivered multiple times (duplicates possible).

3. Exactly once — a message is delivered exactly once, with no losses or duplicates. This is the most complex guarantee, implemented using idempotent producers and transactions.

Which ones I have encountered:

• Usually, the at least once guarantee is used, where the producer confirms the record, and the consumer processes it while maintaining offsets after successful processing.
• For critical systems, the exactly once mode with transactions was used to avoid duplicates in case of failures.

Example of configuring a producer for idempotency in Go (using the sarama library):

config := sarama.NewConfig()
config.Producer.Idempotent = true
config.Producer.RequiredAcks = sarama.WaitForAll
config.Producer.Retry.Max = 5

producer, err := sarama.NewSyncProducer(brokers, config)

Thus, the choice of guarantee depends on the system's reliability and performance requirements.