elastic-apm-node/start cannot load config with type 'module'

[caritasverein]

Describe the bug

When using --experimental-modules with the corresponding "type": "module", inside the package.json, the elastic-apm-node/start module is unable to load the config file:

Elastic APM initialization error: Can't read config file /home/luca/routeplanner-service/elastic-apm-node.js
Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /home/luca/routeplanner-service/elastic-apm-node.js
require() of ES modules is not supported.
require() of /home/luca/routeplanner-service/elastic-apm-node.js from /home/luca/routeplanner-service/node_modules/elastic-apm-node/lib/config.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules.
Instead rename elastic-apm-node.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from /home/luca/routeplanner-service/package.json.

To Reproduce

Steps to reproduce the behavior:

1. Create a project that imports elastic-apm-node/start
2. Create the config file elastic-apm-node.js
3. Set the type: "module" setting in package.json
4. Launch project using --experimental-modules

Expected behavior

The elastic-apm-node/start is expected to load the configuration correctly using either the .cjs extension or making it available as an imported module itself.

Environment (please complete the following information)

• OS: WSL Ubuntu 18.04
• Node.js version: v13.7.0
• APM Server version: ?
• Agent version: 3.3.0

How are you starting the agent? (please tick one of the boxes)

• [ ] Calling agent.start() directly (e.g. require('elastic-apm-node').start(...))
• [x] Requiring elastic-apm-node/start from within the source code
• [ ] Starting node with -r elastic-apm-node/start

Additional context

• Agent config options
  Click to expand

  {
  // Override service name from package.json
  // Allowed characters: a-z, A-Z, 0-9, -, _, and space
  serviceName: 'routeplanner-service',
  // Use if APM Server requires a token
  secretToken: '',
  
  // Set custom APM Server URL (default: http://localhost:8200)
  serverUrl: '',
  active: true,
  }
  

• package.json dependencies:
  Click to expand

  "name": "routeplanner-service",
  "version": "1.0.0",
  "description": "",
  "module": "index.js",
  "type": "module",
  "scripts": {
  "start": "node --experimental-modules --es-module-specifier-resolution=node -r elastic-apm-node/start ./index.js",
  "debug": "node --experimental-modules --es-module-specifier-resolution=node --inspect-brk ./index.js"
  },
  ...
  }
  

[delvedor]

I have a similar issue when using native ESM in node v14 with "type":"module" and Fastify, I was able to solve it with this workaround:

// app.js
export default async function (fastify, opts) { ... }

// index.cjs
const apm = require('elastic-apm-node')
apm.start({ ... })

const fastify = require('fastify')({ logger: true })
fastify.register(import('./app.js'))
fastify.listen(3000)

And run the code with:

node index.cjs

@trentm let me know if I can help debug this one!

[smoke]

When forcing ECMAScript modules using "type": "module" in package.json or in other way as per https://nodejs.org/api/esm.html#enabling, I have managed to workaround this by forcing CommonJS modules for Elastic APM only in the following way:

// package.json
...
  "type": "module",
  "main": "app.js",
...

// app.js
import apm from './elastic-apm-node-start.cjs';

// elastic-apm-node-start.cjs
module.exports = require('elastic-apm-node').start(require('./elastic-apm-node.cjs'));

// elastic-apm-node.cjs
// @see https://www.elastic.co/guide/en/apm/agent/nodejs/current/configuration.html
module.exports = {
  serviceName: 'my-service'
}

[trentm]

My intent is to take this after early ESM work is in (https://github.com/elastic/apm-agent-nodejs/pull/3381). That work isn't required to improve here, but it is loosely related.

My plan is to:

1. Improve the error message to make it clearer that the issue is that "elastic-apm-node.js" for config doesn't work from a type:"module" package.
2. Then add support for "elastic-apm-node.cjs" that will be looked for first. In a type:"module" package we will be able to require("path/to/elastic-apm-node.cjs").

I notice that eslint config files do the same thing regarding a .cjs file and not supporting an ESM config file: https://eslint.org/docs/latest/use/configure/configuration-files

JavaScript (ESM) - use .eslintrc.cjs when running ESLint in JavaScript packages that specify "type":"module" in their package.json. Note that ESLint does not support ESM configuration at this time.