Dockerize Flask: Error: While importing 'app', an ImportError was raised

Question

I am trying to dockerize my Flask API. As soon as I try to start my image I receive the message:

* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off
Usage: python -m flask run [OPTIONS]
Try 'python -m flask run --help' for help.

Error: While importing 'app', an ImportError was raised.

If I am starting the Flask App with my terminal python -m flask run everything works like intended. And right now I am stuck on this problem.

Here is my Code:

from flask import Flask
from bson import json_util
from flask_pymongo import PyMongo
from flask_cors import CORS
import json

app = Flask(__name__)
app.config["MONGO_URI"] = "mongodb://194.163.147.192:27017/test"
CORS(app)
mongo = PyMongo(app)


def parse_json(data):
    return json.loads(json_util.dumps(data))


@app.route('/')
def home():
    return 'Hello'


@app.route('/residential', methods=['GET'])
def find_residential():  # put application's code here
    test = mongo.db.acs.find_one({"name": "Residential"})
    response = Flask.jsonify(parse_json(test))
    response.headers.add('Access-Control-Allow-Origin', '*')
    return response


@app.route('/commercial', methods=['GET'])
def find_commercial():  # put application's code here
    test = mongo.db.acs.find_one({"name": "Commercial"})
    response = Flask.jsonify(parse_json(test))
    response.headers.add('Access-Control-Allow-Origin', '*')
    return response


@app.route('/healthcare', methods=['GET'])
def find_health_care():  # put application's code here
    test = mongo.db.acs.find_one({"name": "Health Care"})
    response = Flask.jsonify(parse_json(test))
    response.headers.add('Access-Control-Allow-Origin', '*')
    return response


@app.route('/germany', methods=['GET'])
def find_germany():
    test = mongo.db.germanies.find_one()
    response = Flask.jsonify(parse_json(test))
    response.headers.add('Access-Control-Allow-Origin', '*')
    return response


if __name__ == '__main__':
    app.debug = False
    app.run()

My requirements.txt looks like this

bson==0.5.10
click==8.0.3
colorama==0.4.4
Flask==2.0.2
Flask-Cors==3.0.10
Flask-PyMongo==2.3.0
itsdangerous==2.0.1
Jinja2==3.0.2
MarkupSafe==2.0.1
pymongo==3.12.1
python-dateutil==2.8.2
six==1.16.0
Werkzeug==2.0.2

My Dockerfile looks like this

FROM python:3.8-slim-buster
WORKDIR /api
COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt
COPY . .
CMD [ "python3", "-m" , "flask", "run", "--host=0.0.0.0"]

I am thankful for any help :)

Project structure is like:

API
L venv
L app.py
L Dockerfile
L requirements.txt

Answer 1

Not sure if it will help... but I had the same issue too and I've just fixed it changing my entrypoint.sh file.

Before I was starting the flask app using:

flask run --host 0.0.0.0 --port 5000

And now I'm using gunicorn:

gunicorn -b 0.0.0.0:5000 app:app

So I had to add gunicorn in the requirements.txt file too.

Answer 2

Your issue is, I think, with your requirements file. In that you include bson as a dependency, which is also included in the pymongo library. See this question. Removing it seems to solve the issue:

 ~/tmp/so_q $ docker build -t myimage .                                                             8s nathanielford@nford 20:51:04
Sending build context to Docker daemon   5.12kB

...

Successfully tagged myimage:latest
 ~/tmp/so_q $ docker run myimage                                                                   13s nathanielford@nford 20:51:26
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on all addresses.
   WARNING: This is a development server. Do not use it in a production deployment.
 * Running on http://192.168.9.2:5000/ (Press CTRL+C to quit)