Heroku Node app keeps crashing - node.js

Question

I have an Express app hosted on Heroku. Locally it runs just fine, but keeps crashing on Heroku. Every time I go to it I get the 'Application Error' page.
I double checked all environment variables and they seem ok.
The Heroku logs don't exactly offer much help:
2017-04-16T23:02:49.001768+00:00 heroku[web.1]: State changed from crashed
to starting
2017-04-16T23:02:52.072906+00:00 heroku[web.1]: Starting process with
command `npm run start`
2017-04-16T23:02:56.042611+00:00 app[web.1]:
2017-04-16T23:02:56.042628+00:00 app[web.1]: > my-app#0.0.1 start /app
2017-04-16T23:02:56.042629+00:00 app[web.1]: > node bin/app
2017-04-16T23:02:56.042630+00:00 app[web.1]:
2017-04-16T23:02:57.200912+00:00 heroku[web.1]: State changed from starting
to crashed
2017-04-16T23:02:57.201454+00:00 heroku[web.1]: State changed from crashed
to starting
2017-04-16T23:02:57.192198+00:00 heroku[web.1]: Process exited with status 0
2017-04-16T23:03:00.981528+00:00 heroku[web.1]: Starting process with
command `npm run start`
2017-04-16T23:03:04.312475+00:00 app[web.1]:
2017-04-16T23:03:04.312489+00:00 app[web.1]: > my-app#0.0.1 start /app
2017-04-16T23:03:04.312490+00:00 app[web.1]: > node bin/app
2017-04-16T23:03:04.312491+00:00 app[web.1]:
2017-04-16T23:03:06.093211+00:00 heroku[web.1]: Process exited with status 0
2017-04-16T23:03:06.112842+00:00 heroku[web.1]: State changed from starting
to crashed
So then I tried starting the app manually:
$ heroku run bash
...
$ npm run start
I got no errors. I'm using the pm2 process manager, so I checked it to see if the app is running and it seems like it is:
$ node_modules/.bin/pm2 list
...
But then when I go to open my app I get the same 'Application error' page as before.
'heroku restart' doesn't help. It just crashes again every time.
The only difference between my local environment and Heroku (as far as I can tell at least...) is that locally I have a file from which I'm reading a RSA private key, and on Heroku that key is read from the environment.
Edit: As requested, here's my Procfile:
web: npm run start
Any ideas?

Answer 1

Your app need to start listening to the port defined in the env. For example if you have an expressjs app it should look something like this:
const express = require('express')
const app = express()
const port = process.env.PORT || 3000
app.get('/', (req, res) => res.send("Hello world"))
app.listen(port, () => console.log(`Example app listening on port ${port}!`))
If the app does not bind to the correct port, heroku is going to consider the app unhealthy and will terminate it.
You need to see this line in the logs, which indicates that heroku recognized the app as healthy:
State changed from starting to up
Keep in mind that this port thing is a special requirement for the web process. The other processes in your app does not have such a requirement.

Answer 2

Try 2 things:
Change your procfile:
web: node start.js
Then make sure that your web process it running by scaling it up:
heroku ps:scale web=1
On your computer in a terminal window run this command in your project:
heroku local web
It simulates how Heroku runs your app and should give you information of what is happening.