Using socket.io with memcached in multiple servers (Auto Scaling)

Question

I'm using this memcached package and I'm trying to get data from my server that store my PHP sessions with memcache. Whenever someone enters my website, a value is stored in the variable $_SESSION["user"] (used to chat) and I want to get that values to use with socket.io (to define who is online and send messages, regardless of the server), because if I am connected to server 2 , whoever is on server 1 can't see me online or send me messages, so, I did:

var express = require("express"),
    app = express(),
    http = require("http").Server(app),
    io = require("socket.io")(http),
    Memcached = require("memcached"),
    users = {};

// app.use(express.static(__dirname + "/scripts"));

io.on("connection", function(socket) {
    var mem = new Memcached("privateipofmymemcachedserver:11211");

    mem.get("user", function(err, data) {
        if(err) {
            return console.error(err);
        }

        if(data === false) {
            return console.error("Data no found!");
        }

        console.log("Data: " + data);
    });

    // From client, sended when $(document).ready()
    socket.on("connected", function(data) {
        socket.user = data.user;

        if(!users[socket.user]) {
            users[socket.user] = new Set();
        }
        users[socket.user].add(socket);

        updateUsers();
    });

    // To update online users list
    function updateUsers() {
        io.emit("users", Object.keys(users));
    }
});

var port = Number(process.env.PORT || 8000);

http.listen(port, function() {
    console.log("Server running on 8000!");
});

But, when I run the code and go to console, the only thing that returns is:

Data: undefined
Data: undefined
Data: undefined

How can I "fix" it? Or is there any better way to do this without involving PHP sessions, just with the socket itself and its functions? Using socket or express cookies, perhaps? I also read about Redis, if it is a good option, how could I adapt my code to use it?

Answer 1

If you are using using elastic beanstalk, look into enabling sticky sessions on your load balancer. This will fix your issue.. There is also a way of doing this with a socket.io adapter but socket.io-memcached lib is not maintained anymore it seems. I would recommend you switch to redis if you want to use an adapter . – mkhanoyan