Redis is an extremely fast, open source, in-memory key value store. Redis has a useful Pub/Sub mechanism that we will use to push messages to a Socket.IO subscriber that will emit events to the client.

Visit this website in order to download and install Redis: http://redis.io/download.

Once Redis is installed, you can start it with the following command:

redis-server

In order to start the Redis command-line interface, CLI issues the following command:

redis-cli

The following commands can be issued from the CLI:

In order to use Redis in our application, install the node-redis client, as follows:

npm install redis --save

Let's configure our application to use Redis by updating the./lib/config/*.json config files with the following configuration:

  "redis": {
    "port": 6379
  , "host": "localhost"
  }

First, we create a simple module, Redis, that wraps up the Redis connection ./lib/cache/redis.js. We start by importing the redis module. We define a Redis module, which calls createClient in order to create a Redis client.

We pull in the Redis configuration data from the preceding:

var redis = require('redis')
, config = require('../configuration'),

function Redis() {
  this.port = config.get("redis:port");
  this.host = config.get("redis:host");
  this.password = config.get("redis:password");
  this.client = redis.createClient(this.port, this.host);
  if (this.password) this.client.auth(this.password, function() {});
}

module.exports = Redis;

Let's extend our Redis module and create a Publisher module that will publish messages using the Redis Pub/Sub feature, ./lib/cache/publisher/index.js. We start by importing our Redis module and use the util module to extend the Redis module with the Publisher module. We then define our Publisher module, which includes a save function, which saves an object as a string to Redis and a publish function, which publishes a message to Redis.

The Publisher module is defined as shown in the following code snippet:

var Redis = require('../../cache/redis')
  , util = require('util'),

util.inherits(Publisher, Redis);

function Publisher() {
  Redis.apply(this, arguments);
};

Redis.prototype.save = function(key, items) {
  this.client.set(key, JSON.stringify(items));
};

Redis.prototype.publish = function(key, items) {
  this.client.publish(key, JSON.stringify(items));
};

module.exports = Publisher;

Next, we extend our Redis module and create a Subscribe r./lib/cache/subscriber/index.js, which consumes published messages. We start by importing our Redis module and use the util module to extend the Redis module with the Subscriber module. We then define our Subscriber module, which includes a subscribe function. This allows the user to subscribe to messages on a key:

var Redis = require('../../cache/redis')
  , util = require('util'),

util.inherits(Subscriber, Redis);

function Subscriber() {
  Redis.apply(this, arguments);
};

Subscriber.prototype.subscribe = function(key) {
  this.client.subscribe(key);
};

module.exports = Subscriber;