Python web application with OpenCV in Heroku

Question

I am building a web application that uses OpenCV in its back-end. I have built the application on Ubuntu (and I tried it on Windows, too) and it works fine. Currently, I am trying to configure OpenCV to work on Heroku. As OpenCV is not possible to be loaded using pip, I read about using heroku buildpacks which provide customization for the server environment.

The following is my attempt to test two of OpenCV buildpacks:

1. I build simple web server with Flask that tries to import OpenCV:

   #hello.py
   import os 
   from flask import Flask
   
   app = Flask(__name__)  
   @app.route("/")
   def hello():
       text = ''
       try:
           import cv2
           text = 'success' 
       except:
           text = 'fail'
           pass
       return text + ' to load openCV'
   
   if __name__ == "__main__":
       port = int(os.environ.get("PORT", 5000))
       app.run(host='0.0.0.0', port=port)
   

   The above code should return either success or fail in loading OpenCV.

2. Then I configured Heroku to use (heroku multi buildpack) by running the following command:

   heroku buildpacks:set https://github.com/ddollar/heroku-buildpack-multi

3. In the .buildpacks file (that is required by multi buildpack) I put the https://github.com/heroku/heroku-buildpack-python and https://github.com/slobdell/heroku-buildpack-python-opencv-scipy buildpacks.

   The first one is for compiling a python application and for installing other modules (e.g., Flask) through pip. The second buildpack is the one that is supposed to load OpenCV.

After all, the whole application did not work!

I got (Application Error) page in Heroku as following screenshot:

I tried to use other buildpack (https://github.com/diogojc/heroku-buildpack-python-opencv-scipy) but I got the same result.

My questions are:
What is wrong in the steps I did?
How should I call (or use) OpenCV within my application in heroku?
Should I use import statement or some other commands?

Answer 1

I could install by doing as follows:

1. cd /path/to/your/dir && git init

2. heroku create MYAPP (start from scratch)

3. heroku config:add BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi.git --app MYAPP

4. create .buildpacks as follows:

   https://github.com/heroku/heroku-buildpack-python
   https://github.com/diogojc/heroku-buildpack-python-opencv-scipy#cedar14
   

5. git add . && git commit -m 'MESSAGE' && git push heroku master

Answer 2

For anyone seeing this today and having the same issue, switch opencv-python in your requirements.txt to opencv-python-headless. This sidesteps the problem with the problematic library file.