client.js

const http = require("http");

let keepAliveAgent = new http.Agent({
    keepAlive: true,
    maxSockets: 5,
    keepAliveMsecs: 60000
});

let name;

const P_REQ_COUNT = 15;

// make HTTP Request
function callMe(i) {
    return new Promise((resolve, reject) => {

        var options = {
            host: "localhost",
            path: "/" + i,
            port: 3001,
            agent: keepAliveAgent,
            headers: {
                'x-onecom-rid': 12344,
                Connection: 'keep-alive'
            },
        };

        name = `${options.host}:${options.port}:`;

        var httpReq = http.get(options, function (response) {
            var bodyChunks = [];
            response.on('data', function (chunk) {
                bodyChunks.push(chunk);
            }).on('end', function () {
                console.log("Response recieved for request: ", i);
                log();
                if (i == P_REQ_COUNT) {
                    httpReqDebug();  // Log when all requests are done
                }
                resolve();
            });
        });
        httpReq.setTimeout(3000);
        httpReq.on('timeout', function () {
            console.log("Aborting request...", i);
            httpReq.abort();
        });
        httpReq.on('error', function (err) {
            console.log("Error recieved: ", i, err.message);
            log();
            reject();
        });
        console.log("Making request: ", i);
        log();
        httpReq.end();

    })
}

(async function () {
    for (let i = 0; i < P_REQ_COUNT; i++) {

        // await callMe(i+1); // Series

        callMe(i + 1); // parallel
    }
})();

async function httpReqDebug() {
    await sleep(2000);
    console.log("After 2 sec....");
    log();
    await sleep(3000);
    console.log("After 5 sec....");
    log();
    await sleep(5000);
    console.log("After 10 sec....");
    log();
    await sleep(5000);
    console.log("After 15 sec....");
    log();
}

function sleep(time) {
    return new Promise((r, re) => setTimeout(() => r(), time));
}
function log() {
    console.log("++++++++++++++++++++++++")
    console.log('Active Sockets => ', (keepAliveAgent.sockets[name] || []).length);
    console.log('Queued Requests => ', (keepAliveAgent.requests[name] || []).length);
    console.log('Free Sockets Pool=> ', (keepAliveAgent.freeSockets[name] || []).length);
    console.log("++++++++++++++++++++++++")
}