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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. io.to("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 worksDiagram of how the Redis adapter works

The source code of this adapter can be found here.

Installation

npm install @socket.io/redis-adapter redis

For TypeScript users, you will also need to install @types/redis if you are using redis@3.

Usage

import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
import { createClient } from "redis";

const io = new Server();

const pubClient = createClient({ url: "redis://localhost:6379" });
const subClient = pubClient.duplicate();

Promise.all([pubClient.connect(), subClient.connect()]).then(() => {
io.adapter(createAdapter(pubClient, subClient));
io.listen(3000);
});

Note: with redis@3, calling connect() on the Redis clients is not needed:

import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
import { createClient } from "redis";

const io = new Server();

const pubClient = createClient({ url: "redis://localhost:6379" });
const subClient = pubClient.duplicate();

io.adapter(createAdapter(pubClient, subClient));
io.listen(3000);

Or with ioredis:

import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
import { Cluster } from "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);

Options

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

Common questions

Is there any data stored in Redis?

No, the Redis adapter uses the Pub/Sub mechanism to forward the packets between the Socket.IO servers, so there are no keys stored in Redis.

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.

Migrating from socket.io-redis

The package was renamed from socket.io-redis to @socket.io/redis-adapter in v7, in order to match the name of the Redis emitter (@socket.io/redis-emitter).

To migrate to the new package, you'll need to make sure to provide your own Redis clients, as the package will no longer create Redis clients on behalf of the user.

Before:

const redisAdapter = require("socket.io-redis");

io.adapter(redisAdapter({ host: "localhost", port: 6379 }));

After:

const { createClient } = require("redis");
const { createAdapter } = require("@socket.io/redis-adapter");

const pubClient = createClient({ url: "redis://localhost:6379" });
const subClient = pubClient.duplicate();

io.adapter(createAdapter(pubClient, subClient));
tip

The communication protocol between the Socket.IO servers has not been updated, so you can have some servers with socket.io-redis and some others with @socket.io/redis-adapter at the same time.

Latest releases

Complete changelog

Emitter

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

Diagram of how the Redis emitter worksDiagram of how the Redis emitter works

This emitter is also available in several languages:

Installation

npm install @socket.io/redis-emitter redis

Usage

import { Emitter } from "@socket.io/redis-emitter";
import { createClient } from "redis";

const redisClient = createClient({ url: "redis://localhost:6379" });

redisClient.connect().then(() => {
const emitter = new Emitter(redisClient);

setInterval(() => {
emitter.emit("time", new Date);
}, 5000);
});

Note: with redis@3, calling connect() on the Redis client is not needed:

import { Emitter } from "@socket.io/redis-emitter";
import { createClient } from "redis";

const redisClient = createClient({ url: "redis://localhost:6379" });
const emitter = new Emitter(redisClient);

setInterval(() => {
emitter.emit("time", new Date);
}, 5000);

Please refer to the cheatsheet here.

Migrating from socket.io-emitter

The package was renamed from socket.io-emitter to @socket.io/redis-emitter in v4, in order to better reflect the relationship with Redis.

To migrate to the new package, you'll need to make sure to provide your own Redis clients, as the package will no longer create Redis clients on behalf of the user.

Before:

const io = require("socket.io-emitter")({ host: "127.0.0.1", port: 6379 });

After:

const { Emitter } = require("@socket.io/redis-emitter");
const { createClient } = require("redis");

const redisClient = createClient();
const io = new Emitter(redisClient);

Latest releases

Complete changelog