How to guarantee message delivery?

Message delivery can be guaranteed using the following approaches:

• Acknowledgements: The sender waits for confirmation from the receiver or broker that the message has been received and processed.

• Retry: If confirmation is not received, the message is sent again.

• Message identifiers: Using unique IDs to track and prevent duplication.

• Message storage: Messages are stored in a reliable storage until delivery is confirmed.

• Use of transactions: In some systems, transactions can be used for atomic sending and processing of messages.

Example: In message queue systems (e.g., RabbitMQ, Kafka), delivery is guaranteed through acknowledgements and retries. It is also important to consider the levels of delivery guarantee — from "at most once" to "exactly once," which require different implementations.