What problem can occur with sending events to the message broker and how to solve it?

When sending events to a message broker (such as Kafka, RabbitMQ), there can be issues with message loss due to network failures, broker unavailability, or errors in the sending code. This results in events not reaching consumers, which violates data integrity and application logic.

To address this problem, the following approaches are used:

• Acknowledgment: use mechanisms to confirm successful message delivery by the broker.
• Retry: implement retries with exponential backoff upon failure.
• Idempotency: make message sending idempotent so that resending does not cause duplication.
• Transactions: use the broker's transactional capabilities, if available, to ensure atomicity of operations.
• Buffering: temporarily store events locally (e.g., in a queue or database) until successful delivery is confirmed.

Example using Kafka Producer in Go with retries:

func sendMessage(producer sarama.SyncProducer, topic string, msg []byte) error {
    message := &sarama.ProducerMessage{
        Topic: topic,
        Value: sarama.ByteEncoder(msg),
    }
    var err error
    for i := 0; i < 3; i++ { // 3 attempts
        _, _, err = producer.SendMessage(message)
        if err == nil {
            return nil
        }
        time.Sleep(time.Duration(i*i) * time.Second) // exponential delay
    }
    return err
}