Message queues decouple producers from consumers, enabling async processing, load leveling, and fault tolerance. When a producer publishes a message, it does not wait for consuming to complete. Brokers (RabbitMQ, SQS, Kafka) store messages durably until acknowledged. Delivery guarantees: at-most-once (fire-and-forget), at-least-once (ack required, duplicates possible), exactly-once (expensive, rare). Dead letter queues (DLQ) capture messages that fail processing repeatedly.
Delivery guarantees and how to handle each.
At-least-once delivery means your consumer will receive the same message multiple times under failure scenarios. Store a processed_message_id table and check before processing. This is mandatory, not optional.
Messages in the DLQ represent unprocessed business events — lost orders, failed payments, unsent notifications. Alert on DLQ size > 0 and investigate immediately. DLQs are not a disposal bin.
Queue depth spikes may be transient. Consumer lag (time from publish to consume) tells you if consumers are keeping up or falling behind. Rising lag with stable depth = consumers too slow.
Sign in to share your feedback and join the discussion.