Apache Kafka Practice Exam 2025 – The Complete All-in-One Guide for Exam Success!

The distinction between 'at-least once' and 'at-most once' delivery in Kafka is crucial for understanding how message delivery semantics affect the design and behavior of distributed systems.

'At-least once' delivery guarantees that messages are processed at least one time. This means that while every message is ensured to reach the consumer, there is a possibility that some messages could be delivered multiple times. This can happen due to retries when acknowledgments from consumers are not received by producers or brokers. This level of assurance is essential in use cases where it is critical not to lose messages, such as logging or event sourcing, even if it leads to processing duplicates that need to be handled by the consumer.

In contrast, 'at-most once' delivery provides the assurance that messages will be processed no more than one time, meaning that there is a risk of messages being lost if a failure occurs before they are acknowledged. This approach is suitable in scenarios where receiving a message once is sufficient and some message loss is acceptable, such as in telemetry data where losing occasional data points does not significantly impact the system.

Therefore, the correct answer highlights the core aspect of 'at-least once' delivery in Kafka, emphasizing the possibility of duplication while ensuring that every message is processed at