What is the difference between point-to-point and publish-subscribe messaging?

Point-to-point delivers each message to a single consumer pulled from a shared pool, well suited for distributing units of work like image-resize jobs across a worker fleet. Publish-subscribe delivers each message to every interested subscriber, well suited for notifying multiple unrelated systems about the same event - for example, an order-placed event that both a billing service and a shipping service need to react to independently.

The key structural difference is coupling: point-to-point couples message throughput to worker capacity, so you add workers to process faster, while publish-subscribe couples message volume to the number of interested subscribers, since each new subscriber gets its own full copy of the stream regardless of how many workers exist per subscriber.

A useful mental shortcut in interviews: if the answer to 'how many systems need this message' is 'exactly one, whichever is free next,' reach for point-to-point; if the answer is 'every system that cares about this kind of event,' reach for publish-subscribe.

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