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Day 4 of 5
⏱ ~60 minutes
Redis in 5 Days — Day 4

Pub/Sub and Streams

Publish messages to channels, subscribe and handle messages, and use Redis Streams for reliable messaging.

Pub/Sub

Pub/Sub is fire-and-forget messaging. Publishers send to channels. Subscribers receive messages on channels they're subscribed to. No message history — if no subscriber is listening when a message arrives, it's lost.

Pub/Sub in Node.js
import { createClient } from 'redis';

// Subscriber needs its own connection
const subscriber = createClient();
const publisher = createClient();
await subscriber.connect();
await publisher.connect();

// Subscribe to a channel
await subscriber.subscribe('notifications', (message) => {
  console.log('Received:', JSON.parse(message));
});

// Publish from elsewhere
await publisher.publish('notifications', JSON.stringify({
  type: 'user_signup',
  userId: 123,
  email: '[email protected]'
}));

// Pattern subscribe (wildcard)
await subscriber.pSubscribe('events:*', (message, channel) => {
  console.log(`Channel ${channel}:`, message);
});
Redis Streams (reliable messaging)
# Streams have a persistent log — messages are stored
# Consumers can read from a specific position
# Consumer groups enable parallel processing

# Add to stream
XADD events * type order_placed userId 123 amount 49.99

# Read from stream
XRANGE events - +               # all messages
XREAD COUNT 10 STREAMS events 0 # from beginning

# Consumer group (parallel workers)
XGROUP CREATE events processors $ MKSTREAM
XREADGROUP GROUP processors worker1 COUNT 1 STREAMS events >
XACK events processors   # acknowledge processed
📝 Day 4 Exercise
Build a Real-Time Notification System
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Day 4 Summary

  • Pub/Sub: fire-and-forget. Fast, real-time. Messages are lost if no subscriber is active.
  • Streams: persistent log. Messages survive disconnections. Use for reliable event processing.
  • Pub/Sub needs separate connections for publishing and subscribing.
  • Use Streams over Pub/Sub when message delivery must be guaranteed.
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Day 5: Production Redis
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