Error trying to call function .fetchSockets(): timeout reached: only 4 responses received out of 5

[Henrriky]

I am facing an error when fetching sockets with the .fetchSockets function. I'm using cluster-adapter + sticky + pm2 to manage workers.

Code snippet that calls the fetchSockets() function:

const sockets= await io
          .in(`${plataform}-${client}`)
          .fetchSockets();
          
//In other line          
const sockets = (
          await io
            .in(`${plataform}-${client}-${userId}`)
            .fetchSockets()
        )[0];
```
You have triggered an unhandledRejection, you may have forgotten to catch a Promise rejection:
Error: timeout reached: only 4 responses received out of 5
at Timeout._onTimeout (/opt/server/node_modules/@socket.io/cluster-adapter/dist/index.js:358:28)
at listOnTimeout (node:internal/timers:573:17)
at process.processTimers (node:internal/timers:514:7)


I've already tried everything. Furthermore, I already put a try catch around this promise

[darrachequesne]

This might happen if one worker gets killed. In that case, you can simply retry:

const MAX_CALLS = 3

async function fetchSockets() {
  for (let i = 0; i < MAX_CALLS; i++) {
    try {
      return await io.fetchSockets();
    } catch (e) {
      // let's retry
    }
  }
  throw "too many errors";
}

[Henrriky]

Just for context, I'm using the pm2 fork that manages the cluster. I am facing problems in production because of this error, it is a telephony application that manages several clients simultaneously. Could implementing this help with the error? What if the worker dies and triggers the error after the maximum number of attempts?

I don't want to have to quit Socket.io simply because of this error. Also, before this error I was facing connection timeout problem and 100% CPU, I implemented the cluster and it worked, however, now this error haunts me

Edit: It seems that when I use the nodejs native cluster module without using pm2 socket.io it works, however, in scenarios with many simultaneous connections the application starts to trigger "timeout" errors to the client

[darrachequesne]

Could implementing this help with the error?

Yes, it should handle the case when a worker suddenly dies.

Also, before this error I was facing connection timeout problem and 100% CPU however, in scenarios with many simultaneous connections the application starts to trigger "timeout" errors to the client

How many simultaneous connections?

See also: https://socket.io/docs/v4/performance-tuning/#at-the-os-level

[Henrriky]

I implemented these things you gave me in this link, however, not much changed. According to the surveys I carried out, I had more than 2000 connections on socket.io, with several rooms and events, because application is multitenant.

[Henrriky]

Can you help me?

I went back and made a simple script to test Socket.io with load testing with Artillery and get same error. When calling fetchSockets function.

const cluster = require("cluster");
const http = require("http");
const { Server } = require("socket.io");
const numCPUs = require("os").cpus().length;
const { setupMaster, setupWorker } = require("@socket.io/sticky");
const { createAdapter } = require("@socket.io/mongo-adapter");
const { MongoClient } = require("mongodb");

const DB = "mydb";
const COLLECTION = "socket.io-adapter-events";

async function main() {
  if (cluster.isMaster) {
    console.log(`Master ${process.pid} is running on port 3000`);

    const httpServer = http.createServer();

    setupMaster(httpServer, {
      loadBalancingMethod: "least-connection",
    });

    httpServer.listen(3000);

    for (let i = 0; i < numCPUs; i++) {
      cluster.fork();
    }

    cluster.on("exit", (worker) => {
      console.log(`Worker ${worker.process.pid} died`);
      cluster.fork();
    });
  } else {

    console.log(`Worker ${process.pid} started`);
    // const mongoClient = new MongoClient("mongodb://localhost:27017/?replicaSet=rs0");
    const mongoClient = new MongoClient("mongodb://localhost:27017/?directConnection=true");
    await mongoClient.connect();
    try {
      await mongoClient.db(DB).createCollection(COLLECTION, {
        capped: true,
        size: 1e6
      });
    } catch (e) {
      console.log("COLLECTION ALREADY EXISTS")
    }
    const mongoCollection = mongoClient.db(DB).collection(COLLECTION);

    const httpServer = http.createServer();
    const io = new Server(httpServer);

    io.adapter(createAdapter(mongoCollection));
    setupWorker(io)

    io.engine.on("connection", (rawSocket) => {
      rawSocket.request = null;
    });

    io.on('connection', async (socket) => {

      console.log('Novo cliente conectado:', socket.id);

      socket.join(`-tenant-${socket.id}`)
      socket.emit(`-tenant-${socket.id}`, "ola")
      socket.join(`-electron-${socket.id}`)
      socket.join(`-teams-${socket.id}`)
      try {
        const electronSockets = await io.in(`-tenant-${socket.id}`).fetchSockets();
        socket.emit(electronSockets.toString());
      } catch (error) {
        console.log("==============================> JA ERA CAIU")
      }

      io.in(`${socket.id}-teste`).emit("hello")

      socket.on('chat message', (msg) => {
        console.log('Mensagem recebida:', msg);
        io.emit('chat message', msg);
        io.emit('teste', msg)
      });

      socket.on('disconnect', () => {
        console.log('Cliente desconectado:', socket.id);
      });
    });

    io.engine.on("connection_error", (error) => {
      console.log("=========================> ERRO ", error.message)
    });
  }
}

main();

This is my file of Artillery:

config:
  target: "http://ipaddress:3000"
  phases:
    - duration: 5
      arrivalRate: 10000
  socketio:
    transports: ["websocket"]

scenarios:
  - name: "Simular conexões e eventos"
    engine: socketio
    flow:
        - think: "2"
        - emit:
            channel: "chat message"
            data: "Henrriky"
        - think: 10
        - emit:
            channel: "join"
            data: "test"

• Artillery faces several timeout errors and most of the time the fetchSockets problem occurs
• The machine has 16 CPU cores and 16 GB of RAM. I have already changed the operating system limits in the performance guide

[vr7bd]

I'm facing the same issue. I'm able to reproduce it with this script. I set the number of clients to 5000. Is there any fix for this?

[Henrriky]

I'm facing the same issue. I'm able to reproduce it with this script. I set the number of clients to 5000. Is there any fix for this?

I solve this migrating the source code to Socketioxide of RUST

[vr7bd]

I solve this migrating the source code to Socketioxide of RUST

Are there APIs like fetchSockets to handle clustering or are you running it as a single instance?

[Henrriky]

I solve this migrating the source code to Socketioxide of RUST

Are there APIs like fetchSockets to handle clustering or are you running it as a single instance?

Single instance