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Version: 4.x

Redis adapter

How it works#

The Redis adapter relies on the Redis Pub/Sub mechanism.

Every packet that is sent to multiple clients (e.g."room1").emit() or socket.broadcast.emit()) is:

  • sent to all matching clients connected to the current server
  • published in a Redis channel, and received by the other Socket.IO servers of the cluster

Diagram of how the Redis adapter works

The source code of this adapter can be found here.


npm install redis

For TypeScript users, you will also need to install @types/redis.


const { Server } = require("");const { createAdapter } = require("");const { createClient } = require("redis");
const io = new Server();
const pubClient = createClient({ host: "localhost", port: 6379 });const subClient = pubClient.duplicate();
io.adapter(createAdapter(pubClient, subClient));io.listen(3000);

Or with ioredis:

const { Server } = require("");const { createAdapter } = require("");const { Cluster } = require("ioredis");
const io = new Server();
const pubClient = new Cluster([  {    host: "localhost",    port: 6380,  },  {    host: "localhost",    port: 6381,  },]);
const subClient = pubClient.duplicate();
io.adapter(createAdapter(pubClient, subClient));io.listen(3000);


NameDescriptionDefault value
keythe prefix for the name of the Pub/Sub
requestsTimeoutthe timeout for inter-server requests such as fetchSockets() or serverSideEmit() with ack5000

Common questions#

  • Do I still need to enable sticky sessions when using the Redis adapter?

Yes. Failing to do so will result in HTTP 400 responses (you are reaching a server that is not aware of the Socket.IO session).

More information can be found here.

  • What happens when the Redis server is down?

In case the connection to the Redis server is severed, the packets will only be sent to the clients that are connected to the current server.


The Redis emitter allows sending packets to the connected clients from another Node.js process:

Diagram of how the Redis emitter works

This emitter is also available in several languages:


npm install redis


const { Emitter } = require("");const { createClient } = require("redis");
const redisClient = createClient({ host: "localhost", port: 6379 });const emitter = new Emitter(redisClient);
setInterval(() => {  emitter.emit("time", new Date);}, 5000);

Please refer to the cheatsheet here.