Cannot find module 'elastic-apm-node'

Hi there

I'm new to Elastic APM and I'm using ELK and App server 7.7. I've managed to get APM to talk to ELK.

I've been tasked to monitor Node.JS and I thought I'll start by simply monitoring a simple 'Hello World' code.

I'm using a simple code in app.js like so:

const http = require('http');

const hostname = '';
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);

How do I get a Node JS agent to monitor this?

I have installed agent like so in an offline machine:

sudo npm install elastic-apm-node-3.6.1.tgz --save

I do not know if this is correct since I can't find any doc to show me how to install agent in an offline manner.

I have inserted the following code at the top of app.js:

// Add this to the VERY top of the first file loaded in your app
var apm = require('elastic-apm-node').start({
  // Override service name from package.json
  // Allowed characters: a-z, A-Z, 0-9, -, _, and space
  serviceName: 'testApp',

  // Use if APM Server requires a token
  secretToken: '',

  // Set custom APM Server URL (default: http://localhost:8200)
  serverUrl: ''

Again I do not know if this is correct since I'm not familiar with Node.JS and the doc seems to assume I have a fair grasp of it.

When I run "node app.js", I get the following error:

Error: Cannot find module 'elastic-apm-node'
    at Function.Module._resolveFilename (module.js:476:15)
    at Function.Module._load (module.js:424:25)
    at Module.require (module.js:504:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/home/user/app.js:1:101)
    at Module._compile (module.js:577:32)
    at Object.Module._extensions..js (module.js:586:10)
    at Module.load (module.js:494:32)
    at tryModuleLoad (module.js:453:12)
    at Function.Module._load (module.js:445:3)

Again I do not know if this is even the correct way to insert code but I can't get any more clue out of the documentation.

Can anyone pls assist me? Any step by step instruction will be really helpful. Thanks.