Subscriptions

A subscription is a real-time message delivery destination.

Use subscriptions when clients need current messages with low latency. A subscription is not durable: it exists to push live messages to active consumers, not to store messages for later replay.

If a client disconnects, its subscription is removed. Messages published while the client is offline are not retained for that subscription.

How Subscriptions Receive Messages

A subscription receives messages through a binding to one or more topic filters.

When a producer publishes a message to a matching topic, FlowMQ sends the message to active consumers on that subscription.

Fan-Out

Subscriptions use a fan-out model. Each active consumer receives a copy of each matching message.

This differs from a queue, where each message is assigned to one consumer.

Shared Subscriptions

A shared subscription lets multiple consumers share the same subscription group.

For a shared subscription, each matching message is delivered to one active consumer in the group. This allows consumers to scale out real-time processing without sending every message to every consumer.

If no consumer in the shared subscription is active, matching messages are not retained by the subscription. Use a queue or stream when messages must be held while consumers are offline.

When to Use Subscriptions

Use a subscription for:

• Live notifications
• Dashboards
• Chat or collaboration updates
• Online device or application state

Use a shared subscription when multiple active consumers should share real-time processing.

If consumers need replay or offline recovery, use a stream or queue, or combine the subscription with a durable destination.