Lab -- Deploying to Heroku

By Dave Eargle

Cloud-hosted machine learning platforms such as AWS Sagemaker and whatever GCP calls theirs need to be demystified. Hence, this lab! In the last lab, you make your pickled model accessible via a Flask REST json route. This means that you can “deploy” your machine learning model anywhere you can run a web server. One platform-as-a-service provider is Heroku. Heroku is owned by Salesforce. They give you a way to launch web-accessible apps that run on AWS, without you ever having to configure anything on AWS.

(We could do everything that Heroku does for us on our own on AWS, but that increases complexity, and opens you up to forgetting to turn something “off”, and you’d start incurring $$ costs).

There are various ways to interact with Heroku, but I’m going to have you do the methods that I’m most familiar with.

1. Create a heroku account

Create a heroku account if you don’t already have one.

2. Complete parts of the heroku getting-started-with-python tutorial

Go through the heroku getting-started-with-python tutorial.

In this tutorial, you will:

  • install the heroku cli.
  • clone an example git heroku-ready repository and deploy it to heroku
  • provision a postgresql database and connect it to your app
  • work with a requirements.txt file (you’ve seen this before! and a Procfile (a heroku-specific thing)

3. Deploy your own flask app to Heroku

Using what you learned from the tutorial, get your flask app running on heroku.

Some tips:

Tip 1: Use a production-ready web server

You could run your flask app on heroku via the flask run command, like you do locally, but the flask server is not recommended for a production environment. If you decide to straight-flask anyway as a learning experience, then you need to tell flask to run on $PORT. Your app’s “web dyno” will get a PORT env var set by heroku, and your web process must bind to this port in order to receive traffic via your heroku domain name. You also must listen on, I think. By default, flask runs on host=, and port=5000. You need to bind to$PORT because your app gets traffic reverse-proxied to it from something like nginx that heroku has sitting in front and receiving traffic on typical web ports 80 (for http) and 443 (for https).

If you decide to follow the tutorial’s suggestion and use gunicorn in your Procfile, you need not worry. gunicorn binds to$PORT by default, if the PORT environment variable is defined.

Tip 2: Run locally to do fast development cycles

If you run your app locally using heroku local, your development cycle can be much faster than doing the git-commit-push-wait-for-build-run-heroku-logs flow.

To see errors on your deployed app, use the heroku logs cli comment.

Tip 3: You have two different git remotes now!

When you run heroku create from your project directory, heroku adds a heroku git remote to your .git/config file. (See it by running git remote -v). So now, when you want to push to heroku, you need to specify git push heroku. When you want to push to your github remote, assuming it is called “origin”, do git push origin.


Using the same repo that you’ve been using for the previous labs, do the following:

  • Deploy your app from the previous labs to heroku.
  • Create a new file called that looks just like does, except make it use your heroku domain now.
  • Add a new section to your called Deployed model, and describe something like how the model is hosted on heroku, and how someone who wants to use your model can point at the heroku domain. Specify your heroku domain predict route in your readme.

Then, submit to canvas a link to your github repo.