ModuleNotFoundError: No module named 'app' about uvicorn-gunicorn-fastapi-docker HOT 2 OPEN

I've just had a similar error.
I solved it this way.

My source code directory is app.
DockerFile "COPY"
"./app" "/app" 이라
formed by a structure called /app/app
You change Dockerfile.

COPY . /app

OR

COPY ./app /app_code
WORKDIR /app_code

from uvicorn-gunicorn-fastapi-docker.

@JaeHyunL nailed it! Thank you, whoever you are!

I am using the Heroku container stack. My Dockerfile looked like this:

FROM tiangolo/uvicorn-gunicorn-fastapi:python3.11-slim

COPY ./requirements.txt /app/requirements.txt

RUN pip install --no-cache-dir --upgrade -r /app/requirements.txt

COPY ./app /app

I changed it to this (appended /app on the COPY line):

FROM tiangolo/uvicorn-gunicorn-fastapi:python3.11-slim

COPY ./requirements.txt /app/requirements.txt

RUN pip install --no-cache-dir --upgrade -r /app/requirements.txt

COPY ./app /app/app

Also, FWIW, my heroku.yml file looks like this:

build:
  docker:
    web: Dockerfile
run:
  web: sh /start.sh

from uvicorn-gunicorn-fastapi-docker.