Gunicorn Error ModuleNotFoundError: No module named 'api' (flask+docker)

Question

Im working on a sample flask app (running ok) and i want to dockerize it. Porject structure is:

Environment vars:
export FLASK_APP=api/app.py
export FLASK_ENV=development

Directory:

Dokerfile api/

• app.py
• __ init __.py (empty)
• config.py
• requirements.txy (flask, gunicorn)

api.py

from flask import Flask
from os import environ as env

app = Flask(__name__, static_folder='../build', static_url_path='/')
# Get config from flask_env
app.config.from_object(f"api.config.{env['FLASK_ENV'].capitalize()}Config")

@app.route("/")
def hello_world():
    return "Hello, World!"

Dokerfile

FROM python:3.6.9
WORKDIR /api

COPY api ./
RUN pip install -r requirements.txt
ENV FLASK_APP api/app.py
ENV FLASK_ENV development

EXPOSE 5000
CMD ["gunicorn", "-b", ":5000", "api.app:app"]

flask run (works)

gunicorn -b 127.0.0.1:5000 api.app:app (works)

docker build -f Dockerfile -t flask-app-api . (works)

12:52 $ docker build -f Dockerfile -t flask-app-api .
Sending build context to Docker daemon  69.12kB
Step 1/8 : FROM python:3.9
 ---> 716d7c7b7a80
Step 2/8 : WORKDIR /api
 ---> Using cache
 ---> 39ef3aa33606
Step 3/8 : COPY api ./
 ---> Using cache
 ---> 40094c83cd4b
Step 4/8 : RUN pip install -r requirements.txt
 ---> Using cache
 ---> faaa3eb08ac3
Step 5/8 : ENV FLASK_APP api/app.py
 ---> Using cache
 ---> abef46437fce
Step 6/8 : ENV FLASK_ENV development
 ---> Using cache
 ---> 14b5e8d8bc3c
Step 7/8 : EXPOSE 5000
 ---> Using cache
 ---> aa21d96a89f4
Step 8/8 : CMD ["gunicorn", "-b", ":5000", "api.app:app"]
 ---> Using cache
 ---> 9d5b5990fe93
Successfully built 9d5b5990fe93

docker run --rm -p 5000:5000 flask-app-api (Error)

[2022-03-16 11:54:35 +0000] [1] [INFO] Starting gunicorn 20.1.0
[2022-03-16 11:54:35 +0000] [1] [INFO] Listening at: http://0.0.0.0:5000 (1)
[2022-03-16 11:54:35 +0000] [1] [INFO] Using worker: sync
[2022-03-16 11:54:35 +0000] [7] [INFO] Booting worker with pid: 7
[2022-03-16 11:54:35 +0000] [7] [ERROR] Exception in worker process
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/gunicorn/arbiter.py", line 589, in spawn_worker
    worker.init_process()
  File "/usr/local/lib/python3.9/site-packages/gunicorn/workers/base.py", line 134, in init_process
    self.load_wsgi()
  File "/usr/local/lib/python3.9/site-packages/gunicorn/workers/base.py", line 146, in load_wsgi
    self.wsgi = self.app.wsgi()
  File "/usr/local/lib/python3.9/site-packages/gunicorn/app/base.py", line 67, in wsgi
    self.callable = self.load()
  File "/usr/local/lib/python3.9/site-packages/gunicorn/app/wsgiapp.py", line 58, in load
    return self.load_wsgiapp()
  File "/usr/local/lib/python3.9/site-packages/gunicorn/app/wsgiapp.py", line 48, in load_wsgiapp
    return util.import_app(self.app_uri)
  File "/usr/local/lib/python3.9/site-packages/gunicorn/util.py", line 359, in import_app
    mod = importlib.import_module(module)
  File "/usr/local/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 972, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 984, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'api'
[2022-03-16 11:54:35 +0000] [7] [INFO] Worker exiting (pid: 7)
[2022-03-16 11:54:35 +0000] [1] [INFO] Shutting down: Master
[2022-03-16 11:54:35 +0000] [1] [INFO] Reason: Worker failed to boot.

python --version
Python 3.6.9

¿Some help?

Answer 1

Probably lost two days with a ton of errors. It seems that having an init.py on the app directory makes Flask to have problems with FLASK_APP and routing. Removed it and problems were solved.