I have a requirement for 9M devices to be communicated to the server, and send messages in every 6seconds, and the amount of data sent from client will be 1KB, and Now I was creating a POC for sockets, and found this library called socket.io.

And My server looks like this:

const { Server } = require('socket.io');
const { hashObjectWithString } = require('./utils');
// Create a basic HTTP server
const server = http.createServer();
const io = new Server(server);


// Socket.IO connection handling
io.on('connection', socket => {
    const clientID = socket.handshake.query?.clientID ?? 'unknown';


    // Listen for 'channel-receive' events 
    socket.on('channel-from-client', (msg, ackCB) => {
        if (ackCB) {
            ackCB('Message Received!');
        }
    });


    // Listen for disconnection
    socket.on('disconnect', () => {
        console.log('Disconnected' + clientID)
    });


    socket.conn.on("close", (reason) => {
        console.log('Disconnected' + clientID)
    });
});

const PORT = process.env.PORT || 8085;

server.listen(PORT, () => {
    console.log(`Server running on port ${PORT}`);
});

And Client Looks Like this:

const io = require('socket.io-client');
const heartbeatJSON = require('../heartbeat.json');

for (let id of Array.from(new Array(100).keys())) {
    const clientID = id;

    const socket = io('http://50.19.44.187:8085', {
        query: {
            clientID
        }
    });

    // Function to send message to server
    const sendMessage = (message) => {
        socket.emit('channel-from-client', message, (ack) => {
            console.log('ACK', ack);
        });
    };

    // Listen for 'chat message' events from server
    socket.on('channel-from-server', (msg, ackCB) => {
        console.log('Received message:', msg);
        if (ackCB) {
            ackCB('Message Received! by: ' + clientID);
        }
    });


    socket.on("connect", () => {
        console.log({ msg: " connected ", clientID });
    });

    socket.on("disconnect", () => {
        console.log("Connection disconnected!");
    })
    
    // Start by sending a message
    const time = 6 * 1000;

    setInterval(() => {
        sendMessage(heartbeatJSON);
    }, time);

}

I use docker for running the server in a Aws ec2-t2 micro server (1v cpu, and 1gb mem). and number of users are 100

I use docker stats to get the statistics and My test results looks like this for 6s frequency communication.

 CPU: 28.02% // highest cpu utilization in the 5mins duration
 MEM: 18.43MiB / 952.7MiB        
 NET: 2.75MB / 599kB 

Could someone please explain why this is using more than 25% of the CPU and occasionally less than 10%? I’m at a loss as to why these swings occur; even if I increase the frequency of heartbeat, the CPU consumption started with a higher values above 25%.