Node.js cluster module appears to break socket.io handshake

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I have the following simple WebSocket server built around the Socket.io library:

var PROCESSES = 1,
    cluster   = require('cluster'),
    i;

if (cluster.isMaster) {
    for (i = 0; i < PROCESSES; i++) {
        console.log('Forking worker', i);
        cluster.fork();
    }
} else {
    (function () {
        var server = require('http').Server(),
            io     = require('socket.io')(server);

        io.on('connection', function (socket) {
            socket.on('message', function (message) {
                socket.emit('message', message + ' too!');
            });
        });

        server.listen(8080);
    })();
}

When started, it creates a single server process which listens for websocket connections and echoes the response back to the client:

$ iocat --socketio ws://localhost:8080
> i am hungry
i am hungry too!
> i like you
i like you too!
>

Now, when I change the PROCESSES variable to a number larger than 1, the client can no longer connect.

var PROCESSES = 2,
    ...

...results in...

$ iocat --socketio ws://localhost:8080
> client.on error
$ iocat -v --socketio ws://localhost:8080
> SIOClient> SIOClient: url-> ws://localhost:8080
SIOClient> onError { [Error: xhr poll error] description: 400 }
client.on error

My gut feeling is that the cluster module, when given more than one worker process, inappropriately switches from one process to another mid-handshake. But I would have thought that the entire connection, from the client initiating the handshake to the closing of the socket at the very very end, occurred over one persistent, keep-alive'd connection.

So what exactly is going on here? And how could it be worked around? I'm familiar with the idea of using a Redis store to share state between server processes on different machines, but that feels like too much infrastructure for my use case (collecting a stream of events from the client and replying with an acknowledgement).

asked 1 min ago

smitelli

872

Node.js cluster module appears to break socket.io handshake