Socket.IO Redis adapter for horizontal scaling

Drop-In Redis Adapter for Socket.IO

Socket.IO's Redis adapter replaces the in-memory broadcast mechanism with Redis pub/sub automatically. No changes to your event handlers are needed:

npm install @socket.io/redis-adapter ioredisconst { createClient } = require('redis'); const { createAdapter } = require('@socket.io/redis-adapter'); const { Server } = require('socket.io'); const http = require('http'); const server = http.createServer(); const io = new Server(server); const pubClient = createClient({ url: 'redis://localhost:6379' }); const subClient = pubClient.duplicate(); await Promise.all([pubClient.connect(), subClient.connect()]); io.adapter(createAdapter(pubClient, subClient)); io.on('connection', (socket) => { socket.join('general'); // io.to('general').emit() now works across all nodes io.to('general').emit('user:joined', { id: socket.id }); }); server.listen(3000);

Two separate Redis clients are required: one for publishing and one for subscribing, because a Redis connection in subscribe mode cannot issue other commands. The adapter handles all routing internally. io.to(room).emit() just works across nodes.