Node.js http.request keepAlive

Question

I'm trying to use http.Agent({ keepAlive: true}) on http.request to keep the connection open for future requests.

I created a simple server to log each new connection but when i run my request.js the server logs two new connections.

How can i use the HTTP keep-alive with Node.js native modules?

request.js:

const http = require("http");

const agent = new http.Agent({
    keepAlive: true
});

var req1 = http.request({
    agent: agent,
    method: "GET",
    hostname: "localhost",
    port: 3000
}, function (res1) {
    console.log("REQUEST_1");

    var req2 = http.request({
        agent: agent,
        method: "GET",
        hostname: "localhost",
        port: 3000
    }, function (res2) {
        console.log("REQUEST_2");
    });

    req2.end();
});

req1.end();

server.js:

const http = require('http');

var server = http.createServer(function (req, res) {
    res.end('OK');
    console.log("REQUEST");
})

server.on('connection', function (socket) {
    console.log("NEW CONNECTION");
})

server.listen(3000);

output:

NEW CONNECTION
REQUEST
NEW CONNECTION
REQUEST

Answer 1

Set maxSockets options like this:

const agent = new http.Agent({
    keepAlive: true,
    maxSockets: 1
});

By default maxSockets is set to Infinity - https://nodejs.org/api/http.html#http_new_agent_options

Full example on node v10

const http = require("http");

const agent = new http.Agent({
    keepAlive: true,
    maxSockets: 1
});

var req1 = http.request({
    agent: agent,
    method: "GET",
    hostname: "localhost",
    port: 3000
}, function (res1) {
    console.log("REQUEST_1");

    res1.on('data', function () {
        console.log("REQUEST_1 data");
    });

    res1.on('end', function () {
        console.log("REQUEST_1 end");
    });

    var req2 = http.request({
        agent: agent,
        method: "GET",
        hostname: "localhost",
        port: 3000
    }, function (res2) {
        console.log("REQUEST_2");

        res2.on('data', function () {
            console.log("REQUEST_2 data");
        });

        res2.on('end', function () {
            console.log("REQUEST_2 end");
        });
    });
    req2.end();
});
req1.end();