Error: Redis connection to 127.0.0.1:6379 failed - connect EMFILE - node.js

Question

So I created, an realtime application using socket.io, redis and node.js.
The problem is that with 30 users, I'm already reaching the number of connections of the server ( I'm running Ubuntu 14.04.
And I think it has something to do about the way I connect to redis.
So on one page, I have at most 12 channels to subscribe to. On two socket.io connections, one has 6 channels and the other has the other 6 channels.
Before showing my node js code, what I do, is for each channel, I create a new redis client, so let's say that I have an insert and update channel, on the node.js code, so my code wiil be:
var data = io.of('/data');
data.on('connection', function(client) {
var insert = redis.createClient();
var update = redis.createClient();
insert.subscribe('insert');
insert.on("message", function(channel, message) {
client.emit('data_insert', message);
});
update.subscribe('update');
update.on("message", function(channel, message) {
client.emit('data_update', message);
});
});
I believe that this is the problem, and that why, with 30 users I'm exceeding the limit of connections of the server, since 30 * 12 + 2 * 30 = 420, plus a few others for everything else, and it's easy to reach 1024.
So how can I optimize the code, to reduce the number of connections per client to one or two the max?
Does it help, to have the var insert = redis.createClient(); outside the data.on('connection')??

Answer 1

You should not be creating one (or more) redis connections per client - just keep using the same global one. Further, there's really no reason to create a client for each channel you want to subscribe to. Just use the channel argument to figure out which thing to do with the data (in this case, you're doing the same thing on each channel, so even less point in having separate ones).
var data = io.of('/data');
var redis = redis.createClient();
redis.subscribe('insert');
redis.subscribe('update');
data.on('connection', function(client) {
redis.on("message", function(channel, message) {
if(channel == 'insert')
client.emit('data_insert', message);
else if(channel == 'update')
client.emit('data_update', message);
});
});
There are probably better ways to do this, but this is a fairly direct translation of your code into something that uses only one redis connection.
Note that redis subcribers can only subscribe - you will need a second client to publish or do any other redis operations.

Answer 2

just for your information (I lost this evening with that)
This does not work (it defaults connecting to localhost:6379 whatever you put in the url):
const redisURL = "redis://foo.bar.org:6379"
redis.createClient( redisURL )
but this DOES WORK (it tries to connect too foo.bar.org)
redis.createClient( {url: redisURL} )

Answer 3

Use socket.io's namespace. Within each namespace you can also define rooms but namespace should be enough for your needs.