Getting "Module did not self-register. " when using worker_threads in older heroku apps

[jan-osch]

I I am repeatedly running into this issue. I am getting an error like this, and my worker fails to start:

Module did not self-register. 
    at Object.Module._extensions..node (internal/modules/cjs/loader.js:1003:18) 
    at Module.load (internal/modules/cjs/loader.js:812:32) 
    at Function.Module._load (internal/modules/cjs/loader.js:724:14) 
    at Module.require (internal/modules/cjs/loader.js:849:19) 
    at require (internal/modules/cjs/helpers.js:74:18) 
    at Object.<anonymous> (/app/.heroku/heroku-nodejs-plugin/index.js:1190:19) 
    at __webpack_require__ (/app/.heroku/heroku-nodejs-plugin/index.js:20:30) 
    at Object.<anonymous> (/app/.heroku/heroku-nodejs-plugin/index.js:132:21) 
    at __webpack_require__ (/app/.heroku/heroku-nodejs-plugin/index.js:20:30) 
    at Object.<anonymous> (/app/.heroku/heroku-nodejs-plugin/index.js:102:17)  

I am using a Heroku pipeline for my app, and this issue error occurs only on apps that exist for some time (mainly on staging and on production ); it never happens in the review apps, where the same worker starts without any problem. I guess it might have something to do with staging and production migrating from node v10 to v12 some months ago.

Npm: 6.12.0
Node: v12.13.0
Stack: heroku-18

I have removed almost everything from my worker, and it still happens.

const { parentPort } = require('worker_threads');

parentPort.on('message', async (data) => {
  const { port } = data;
  try {
    const bytecode = Buffer.from('');
    port.postMessage({ bytecode });
  } catch (error) {
    port.postMessage({ error: error.message ? error.message : error.toString() });
  }
  port.close();
});

[jan-osch]

For anyone that encounters this problem - make sure to disable both "Enhanced Language Metrics" and "Node Language Metrics" in metrics settings in Heroku. The current implementation of the metrics system in Heroku is incompatible with some worker_threads scenarios.

[danielleadams]

Spoke with @jan-osch and we discovered that this was the issue. We will hopefully come up with a solution, but this unfortunately won't be a quick fix.

To ensure the feature is turned off, run heroku labs -a APP_NAME and confirm that under App Features that the nodejs-language-metrics feature is disabled.

[danielleadams]

@jan-osch I opened a new issue (heroku/heroku-nodejs-plugin#13) to keep track of the issue, so I'm going to close this one. Thanks for bringing this to our attention!