QuickFix how to deploy a Loopback 4 Application to Heroku

When you are prototyping, sometimes you just need something to work, this was my case with a new experiment I’m working using Loopback 4 which I wanted to deploy for to Heroku for some rapid testing.

Generally CLI generated App’s doesn’t like environments like Heroku too much and since I later will deploy to DigitalOcean through some Docker containers, I just needed a QuickFix.

Anyways, let’s get to the point… this is a very opiniated post which takes for granted you are using the exact same development workflow that I have, if not, post a comment and I will do my best to help you out.

  1. Remove the /dist entry from .gitignore so it will be committed to Git, and subsequently caught by the CD routine running on Heroku through the GitHub Webhook.
  2. Remove the prestart script entry from package.json.
  3. Remove the “-r source-map-support/register” from the start script entry in package.json.

Now you are good to deploy it to Heroku via GitHub, however don’t forget to build before you commit.



Hacks to get Loopback App’s running on Heroku

To get Loopback App’s running on Heroku, a couple of hacks are required due to the way Loopback manages it’s configurations.

The first issue to solve is to get Loopback to take the port number from the environment since Heroku uses arbitrary port numbers to target different applications.

There is probably a more elegant way, however I first wanted to stay out of node_modules files, so I opted to just focus on modifying server.js.

It’s actually very easy, since loopback internally supports passing arguments to the listen function all the way out from the server.js file.
It does this by switching between automatic configuration and explicit configuration from the arguments passed to the listen function.

So, basically it’s just amending the “start” function to fetch the port number from the environment and pass it as argument to the listen function.

I have done it this way…

app.start = function () {
   // start the web server
   var port = process.env.PORT || 8000;
   return app.listen(port, function () {
      console.log('Web server listening at: %s', app.get('url'));