What do you know about delivery guarantees in Kafka?

Kafka has several levels of message delivery guarantees:

1. At most once — a message may be lost but is not duplicated. Usually when the producer is disconnected before acknowledgment.
2. At least once — a message is guaranteed to be delivered, but duplication may occur upon resend.
3. Exactly once — a message is delivered and processed exactly once, without duplicates.

To ensure these guarantees, Kafka uses:

• acks — a producer parameter that determines how many replicas must confirm the write (0, 1, all).
• Message identifiers and offsets — for tracking read position.
• Transactions — to implement exactly-once semantics during message writing and processing.

Example of producer configuration for "at least once" delivery guarantee:

producer, _ := sarama.NewSyncProducer(brokers, &sarama.Config{
    Producer: sarama.ProducerConfig{
        RequiredAcks: sarama.WaitForAll, // wait for confirmation from all replicas
        Retry: sarama.ProducerRetry{
            Max: 5, // retry attempts
        },
    },
})

Thus, Kafka allows flexible configuration to balance between performance and delivery reliability.