Publish-Subscribe (Pub/Sub)

Publish-subscribe is broadcasting for systems: a publisher announces that something happened — an order shipped, a patient admitted — and any number of subscribers, whom the publisher does not know and need not know, receive it. The pattern that lets organisations add listeners to events without rewiring the announcer.

What It Is

In publish-subscribe messaging, producers publish messages to named channels or topics without addressing specific receivers; subscribers declare interest in topics and receive everything published there. The decoupling is multidimensional: publishers don't know subscribers exist, new subscribers can join without any publisher change, and multiple systems can react independently to the same event (inventory reserves stock, analytics records it, email sends confirmation — all from one announcement). It contrasts with point-to-point queues (one message, one consumer) — the two patterns compose, and modern event platforms serve both.

Why It Matters to You

Pub/sub is the architectural answer to the integration problem that grows quadratically: every new system that needs to know about orders cannot simply be wired to the order system, or the wiring eventually outweighs the systems. With an event backbone, the order system announces; whoever needs to know subscribes; adding the eleventh consumer touches nothing. For executives, the pattern explains a class of modern capability: real-time everything (fraud checks, recommendations, alerts reacting to events as they occur) is built on event distribution at this shape. Its governance note: event streams are data flows — they belong on the data map, subject to the same protection questions as any pipeline.

When You'll Meet It

In architecture reviews and integration planning. The diagnostic question when every new integration is a project: 'why is this not an event?'