Queue

A queue distributes work so each message is typically processed by one consumer in a competing consumer group. Producers enqueue; consumers pull or receive push; brokers buffer when consumers lag. Ideal for task distribution, load leveling, and decoupling burst traffic.

Trade-off: ordering is often global or per-queue, not per business key unless partitioned; messages may be redelivered.

On interviews: queue versus topic for order fulfillment workers; ack timing and poison message handling.

Common pitfalls: unbounded queue growth hiding consumer failure; ack before processing; no DLQ.

Checklist:

• Define visibility timeout and ack semantics.
• Monitor queue depth and age of oldest message.
• Route poison messages to DLQ with alerts.
• Size consumers from throughput and SLA.