If the main goal is to ensure message delivery guarantee, which is better to choose: Kafka or RabbitMQ?

The choice between Kafka and RabbitMQ for message delivery guarantees depends on the specific system requirements.

RabbitMQ is initially focused on reliable message delivery with acknowledgments, supporting various acknowledgment modes, persistent queues, and redelivery mechanisms. It is well-suited if a strict guarantee is needed that each message will be processed at least once (at-least-once delivery) or exactly once (exactly-once delivery) with proper configuration.

Kafka was originally designed as a distributed event log with high throughput and scalability. It provides delivery guarantees but emphasizes message order and re-reading capabilities. Kafka supports "at-least-once" and "exactly-once" semantics when using transactions and proper consumer configuration.

If the main task is guaranteed delivery without loss and with acknowledgments, RabbitMQ may be simpler to set up and use for this scenario. Kafka is better suited for high-load systems where order and scalability are important but requires more careful configuration to ensure delivery guarantees.

Example of using RabbitMQ with message acknowledgment in Go:

ch, _ := conn.Channel()
msgs, _ := ch.Consume("queue_name", "", false, false, false, false, nil)

for d := range msgs {
    // process message
    fmt.Printf("Received message: %s", d.Body)
    d.Ack(false) // acknowledge processing
}

Thus, for message delivery guarantees, RabbitMQ is often preferable if massive scaling is not required.