Kafka: Manual acknowledgement in Spring Kafka

@Bean
ConcurrentKafkaListenerContainerFactory<String, String> factory(...) {
    var f = new ConcurrentKafkaListenerContainerFactory<String, String>();
    f.getContainerProperties().setAckMode(ContainerProperties.AckMode.MANUAL);
    return f;
}

@KafkaListener(topics = "orders")
void onOrder(String payload, Acknowledgment ack) {
    process(payload);
    ack.acknowledge();      // only now is the offset committed
}

An exception before acknowledge() means the record is redelivered,
which is the behaviour at-least-once processing depends on.