The flask server is not production ready so we need to use a different server thing. We will use gunicorn. Install like this

pip install gunicorn

Also after you install it make sure to add the updated list of dependencies to your requirements.txt using

pip freeze > requirements.txt

You also need a Procfile so that Heroku can use gunicorn to set stuff up. Create a file called “Procfile” which contains the following

web: gunicorn name-of-flask-app:app

By default heroku deploys using python 3 but we might be using python 2. To get heroku to deploy using your version of python create a runtime.txt file which specifies the version of python you want it to use for deployment. A sample runtime.txt file will contain the following line.

python-2.7.15

Install the heroku cli. Then run

heroku login

To create a heroku project run

heroku create project-name

Im pretty sure what this does is create a heroku project and add the link to the heroku project’s git repository as a remote of your current git repository. You could also create the heroku project through the heroku dashboard and then manually add the heroku project’s git repo link to your current project’s remote.

git remote add heroku link-to-heroku-project-repo.git

This link the heroku project’s git repo can be found on the heroku dashboard for your project under the settings tab.

If you run the following command

git remote -v

You should see something like this

heroku https://git.heroku.com/<some-project-name>.git (fetch)
heroku https://git.heroku.com/<some-project-name>.git (push)
origin https://github.com/Salamander1012/FlaskDecoratorExample.git (fetch)
origin https://github.com/Salamander1012/ FlaskDecoratorExample.git (push)

It’s a list of your remotes. You should see origin, which is the name of the remote on GitHub, and heroku, which is the name of the remote on heroku. Every time you try to push to the remote on heroku using

git push heroku master

Heroku will try and host you server and give you a link to where it is hosted.

When you push to heroku keep your gitignore in mind. If your firebase app credentials are in your gitignore to keep them off of GitHub, when you push to heroku your app won’t work because the version you pushed to heroku also doesn’t have the credentials. To fix this you will need to force add the credentials file when pushing to heroku

git add -f firebase-credentials.json
git commit -m "blah"
git push heroku master

(Not sure if this needs to be done) Make sure to untrack the firebase-credentials file before you push to github. The way I did this is

git rm -r --cached .
git add .
git commit -m "blah"
git push origin master

This untracks all the files, then you add them all back but the firebase-credentials file is ignored because its in the gitignore

To view the logs and check for error details you can do

heroku logs --tail

Or go to your project dashboard and next to “open app” there should be a “more” button. If you click more a dropdown will appear with an option to view logs.