socket.io not emitting to all clients - node.js

Question

I'm running into a strange issue where - in my production environment only (everything works fine in local testing) - socket.emit() works fine but io.emit() does not. In other words, each individual socket client connection can send and receive messages to the server, but when the server emits to all clients, none of them receive the message. This is strange, because it can see all the clients - if I check Object.keys(io.engine.clients) I see the ids of all connected clients. But io.emit() doesn't broadcast to any of them.
I'm using the latest version of node (7.7.4 and socket.io (1.7.3). I'm hosting on Heroku, and have enabled sticky sessions. I use cluster so that all CPUs are utilized, and I have a redis service set up to synchronize all the workers. All of that infrastructure appears to be working just fine.
Why would socket.emit() work for any given socket, but none of the other methods?
socket.on('sendChat', function(messageBundle) {
console.log('sockets: ' + Object.keys(io.engine.clients)) //shows clients
io.sockets.emit('incomingChat', messageBundle); //nothing
io.emit('incomingChat', messageBundle); //also nothing
var clients = Object.keys(io.engine.clients);
for (var i = 0; i < clients.length; i++) {
console.log('broadcasting to: ' + clients[i]);
socket.broadcast.to(clients[i]).emit('incomingChat', messageBundle); //still nothing
}
socket.emit('incomingChat', messageBundle); //this works though
});
UPDATE:
Here is where I define the socket stuff earlier.
var redis = require('redis');
var pub = redis.createClient(redisPort, redisHost, {
auth_pass: redisPwd
});
var sub = redis.createClient(redisPort, redisHost, {
detect_buffers: true,
auth_pass: redisPwd
});
var adapter = require('socket.io-redis');
io.adapter(adapter({
pubClient: pub,
subClient: sub
}));
var cluster = require('cluster');
var WORKERS = process.env.WEB_CONCURRENCY || 3;
if (cluster.isMaster) {
for (var i = 0; i < WORKERS; ++i)
console.log('forking process ' + i);
cluster.fork();
} else {
var express = require('express');
var session = require('express-session');
var app = express();
var server = require('http').createServer(app);
var io = require('socket.io').listen(server);
var port = process.env.PORT || 5000;
server.listen(port, function() {
console.log("Listening on " + port);
console.log("testing");
});
var mySession = session({...}) //this enables me to authenticate the socket using the same session middleware as the express routes
io.use(function(socket, next) {
mySession(socket.handshake, {}, next);
});
io.on('connection', function(socket) {
socket.emit('welcome');
console.log('socket connection');
socket.on(... etc.)
...})
...})
On the client side, the socket connection is initiated using a simple config:
var socket = io({
reconnection: true,
reconnectionDelay: 100,
});

Answer 1

io is undeclared on the beginning, and then You try to redeclare it in the else statement.

Answer 2

For me the issue was mismatching version of socket.io and reddis-adapter (upgraded socket io to 3.0.1 and redis adapter remained at 5.x.x)
Upgrading adapted to 6.0.1 solved it