Heroku + gunicorn not working (bash: gunicorn: command not found )

Question

I successfully install gunicorn:

remote: -----> Removing .DS_Store files
remote: -----> Python app detected
remote: -----> Installing dependencies with pip
remote:        Collecting gunicorn==19.0.0 (from -r requirements.txt (line 1))
remote:          Downloading gunicorn-19.0.0.tar.gz (382kB)
remote:        Installing collected packages: gunicorn
remote:          Running setup.py install for gunicorn
remote:        Successfully installed gunicorn-19.0.0

My Procfile:

web: gunicorn myapp:app --log-file=-

But the app crashes when deployed:

bash: gunicorn: command not found 

I tried adding the heroku python buildpack, but no luck. If I roll back to a previous commit (where requirements.txt and Procile are both unchanged), it works:

heroku/web.1:  Starting process with command `gunicorn myapp:app --log-file=-` 
app/web.1:  2015-10-08 17:04:18 [3] [INFO] Listening at: http://0.0.0.0:51854 (3)

Answer 1

Make sure gunicorn is in your requirements.txt

Answer 2

The issue seemed to fix itself after uninstalling all requirements remotely, and reinstalling them.

Answer 3

If you have both requirements.txt and Pipfile in the project root, then I would recommend to delete the Pipfile and have all your requirements listed in requirements.txt file (including gunicorn).

It will then show: "Installing requirements from pip", and all of your requirements listed in requirements.txt will be installed.

Answer 4

I was missing the heroku/python buildpack so I went to the dashboard and:

Settings -> Add buildpack -> heroku/python

Answer 5

After checking that gunicorn is in requirements.txt run:

pip install -r requirements.txt

My output contained several Requirement already satisfied: ... but gunicorn wasn't installed:

Collecting gunicorn (from -r requirements.txt (line 2))
Using cached ...

Installing collected packages: gunicorn
Successfully installed gunicorn-19.9.0