How would you explain the difference between a queue and a topic?

Compare queues and topics for backend messaging

Compares point-to-point queues with publish-subscribe topics and explains when each model fits.

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TL;DR

A queue is usually point-to-point work distribution: one message is processed by one consumer instance from a consumer group. It is useful for jobs like sending an email or processing an export. A topic is publish-subscribe: one event can be delivered to multiple independent subscriptions. It is useful when several parts of the system need to react to the same business event.

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Point-to-point work distribution, publish-subscribe, fan-out, consumer independence, and delivery semantics.

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Why this question matters
A queue distributes one logical unit of work to one consumer, while a topic delivers one published fact to independent subscriptions. The choice determines ownership, fan-out, scaling, and contract responsibilities.
A queue is usually point-to-point work distribution: one message is processed by one consumer instance from a consumer group. It is useful for jobs like sending an email or processing an export. A topic is publish-subscribe: one event can be delivered to multiple independent subscriptions. It is useful when several parts of the system need to react to the same business event.
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I would choose based on ownership. If one service owns the work and scaling means adding more workers, a queue is a good fit. If an order placed event needs billing, notifications, analytics, and fulfillment to react independently, a topic is cleaner. Topics introduce more contract responsibility because every subscriber depends on the event schema and timing. Queues are simpler when there is only one logical owner of the work.

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Details

Using a topic when there is only one logical consumer.
Using one shared subscription for unrelated consumers.
Publishing internal database-shaped events as public contracts.
Ignoring subscriber failure and dead-letter handling.

How would you explain the difference between a queue and a topic?

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