socket.io and node cluster: dispatch events to sockets - node.js

Question

I have a nodejs cluster server that is using mongo changestream listener, to emit data to clients over socket.io. I'm using Redis to store a userId and the socketId of all the connected users in a hash.
{ userId: 'aaa', socketId: 'bbb' }
The redis clients for storing this data is initialized in the master process.
The mongo changestream is created in the master process.
When the changestream sees a new document, it will send the document to a child process as a message. When the child process receives the message, it can retrieve the userId from the document. With the userId, the socketId for the client connection can be retrieved from redis.
The issue I am having is in trying to emit a message using the socketId after it is retrieved from redis.
I am creating a sockethandler object that contains the socketId. When I use this socketId to emit a socket message, like so:
io.sockets.to(userSocketId)
.emit("confirmOrder", "Your order is being processed!")
I receive an error:
(node:31804) UnhandledPromiseRejectionWarning: Error: The client is closed
at new ClientClosedError (/Users/a999999999/code/*/node_modules/#node-redis/client/dist/lib/errors.js:24:9)
The error is from redis, and originated on the socket emit line written above. ^^
Here is more code from the worker process:
const pubClient = createClient({ host: "127.0.0.1", port: 6379 }),
subClient = pubClient.duplicate();
io.adapter(createAdapter(pubClient, subClient));
setupWorker(io);
io.on("connection", (socket) => {
const socketId = socket.id;
socket.emit("connection", "SERVER: you are connected");
socket.on("userConnect", (user) => {
let { userId } = user;
userConnectClient
.HSET(userId, { userId, socketId })
.catch((err) => console.log("ERROR: ", err));
});
});
process.on("message", async ({ type, data }) => {
switch (type) {
case "dispatch:order":
let { order } = JSON.parse(data);
const socketsHandler = await createSocketsHandler(order);
const userSocketId = socketsHandler.user.socketId;
io.sockets
.to(userSocketId)
.emit("confirmOrder", "Your order is being processed!");
break;
}
});
async function createSocketsHandler(order) {
let { userId } = order;
let user = await userConnectClient
.HGETALL(userId)
.catch((err) => console.log(err));
return {
user: user,
};
}
I am temporarily stumped at this point. Currently experimenting with the io object, and trying to find better tools to monitor redis. Any help/questions is appreciated! Thank you!

Answer 1

I've since realized why the redis client was not working properly. I'm making use of publisher and subscriber clients with redis. The problem was, I was creating the redis clients in the worker process of the server. So, whenever the server is making a command to redis, it is not able to do it properly because there is a pair of clients for each worker process, which is not the proper implementation, I believe.
This was solved by creating the redisClient outside of my cluster server code. ;P My server can now properly subscribe to redis client in master and worker process!