var io = require('socket.io')(3000);
var redis = require('socket.io-redis');
io.adapter(redis({ host: 'localhost', port: 6379 }));

By running socket.io with the socket.io-redis adapter you can run multiple socket.io instances in different processes or servers that can all broadcast and emit events to and from each other.

If you need to emit events to socket.io instances from a non-socket.io process, you should use socket.io-emitter.

uri is a string like localhost:6379 where your redis server is located. For a list of options see below.

The following options are allowed:

• key: the name of the key to pub/sub events on as prefix (socket.io)
• host: host to connect to redis on (localhost)
• port: port to connect to redis on (6379)
• subEvent: optional, the redis client event name to subscribe to (message)
• pubClient: optional, the redis client to publish events on
• subClient: optional, the redis client to subscribe to events on

If you decide to supply pubClient and subClient, make sure you use node_redis as a client or one with an equivalent API.

If you supply clients, make sure you initialized them with the return_buffers option set to true.

You can supply ioredis as a client by providing messageBuffer as the subEvent option.

The redis adapter instances expose the following properties that a regular Adapter does not

• uid
• prefix
• pubClient
• subClient

Access the pubClient and subClient properties of the Redis Adapter instance to subscribe to its error event:

var redis = require('socket.io-redis');
var adapter = redis('localhost:6379');
adapter.pubClient.on('error', function(){});
adapter.subClient.on('error', function(){});

If you need to create a redisAdapter to a redis instance that has a password, use pub/sub options instead of passing a connection string.

var redis = require('redis').createClient;
var adapter = require('socket.io-redis');
var pub = redis(port, host, { auth_pass: "pwd" });
var sub = redis(port, host, { return_buffers: true, auth_pass: "pwd" });
io.adapter(adapter({ pubClient: pub, subClient: sub }));

Make sure the return_buffers option is set to true for the sub client.

The socket.io-redis adapter broadcasts and receives messages on particularly named Redis channels. For global broadcasts the channel name is:

prefix + '#' + namespace + '#'

In broadcasting to a single room the channel name is:

prefix + '#' + namespace + '#' + room + '#'

• prefix: The base channel name. Default value is socket.io. Changed by setting opts.key in adapter(opts) constructor
• namespace: See https://github.com/socketio/socket.io#namespace.
• room : Used if targeting a specific room.

A number of other libraries adopt this protocol including:

• socket.io-emitter
• socket.io-python-emitter

MIT