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Pub/Sub Notifications (Redis Publish/Subscribe)

Demonstrates Redis Publish/Subscribe (Pub/Sub) messaging. A publisher sends messages to a channel, and any number of subscribers listening on that channel receive them in real time.

Sources:

Concept

Role File Responsibility
Publisher api.js Publishes a JSON message to the notifications channel via an HTTP endpoint
Subscriber subscriber.js Subscribes to the notifications channel and logs each received message

Key points:

  • Pub/Sub uses separate Redis connections. A client in subscribe mode cannot run other commands, so the subscriber has its own dedicated client.
  • Pub/Sub is fire-and-forget: messages are delivered only to subscribers connected at the time of publishing. If no subscriber is listening, the message is lost (unlike a queue).
  • publish() returns the number of subscribers that received the message.

Endpoint

POST /notifications/publish-notification

Publish a notification to the notifications channel.

  • Body:
{
	"title": "Hello"
}

title defaults to "Default Title" when omitted. A timestamp is added automatically.

  • Response:
{
	"message": "Notification sent to 1 receivers"
}

The receiver count is 0 when no subscriber is running.

Running the Subscriber

The subscriber is a separate process from the web server. Start both:

# Terminal 1 — API (publisher)
npm run dev

# Terminal 2 — subscriber (listener)
npm run sub

npm run sub runs node src/pub-sub/subscriber.js.

Verifying Delivery

  1. Start the API and subscriber (above).
  2. Publish a notification:
curl -X POST http://localhost:3000/notifications/publish-notification \
	-H "Content-Type: application/json" \
	-d '{"title":"Hello"}'
  1. Watch the subscriber terminal:
Received on notifications : { title: 'Hello', timestamp: '2026-07-29T00:00:00.000Z' }

The HTTP response reports how many subscribers received it (e.g. Notification sent to 1 receivers).

Pub/Sub vs Queues

Pub/Sub Queue (List / BullMQ)
Delivery All active subscribers One consumer per job
Missed messages Lost if no subscriber online Persisted until processed
Use case Real-time broadcast (notifications, events) Reliable background work

See Email Queue (Redis List) and BullMQ Job Queue for the queue-based patterns.