Docker django runs only if I specify the command - django

Question

I am new to docker and I was trying to create an Image for my Django application.
I have created the image using the following Dockerfile
FROM python:3.6-slim-buster
WORKDIR /app
COPY . /app
RUN pip install -r Requirements.txt
EXPOSE 8000
ENTRYPOINT ["python", "manage.py"]
CMD ["runserver", '0.0.0.0:8000']
The problem is when I run the image using
docker run -p 8000:8000 <image-tag>
I am unable to access the app in my localhost:8000
But if I run the container using the command
docker run -p 8000:8000 <image-tag> runserver 0.0.0.0:8000
I can see my app in localhost:8000

Answer 1

I think that you can use only Entrypoint command.
Try with:
FROM python:3.6-slim-buster
WORKDIR /app
COPY . /app
RUN pip install -r Requirements.txt
EXPOSE 8000
ENTRYPOINT ["python", "manage.py", "runserver", "0.0.0.0:8000"]
Or you can write script file (entrypoint.sh) with the line. And maybe you can run makemigrations and migrations in the same file.

Answer 2

You need to change the single quotes to double quotes in your CMD line.
Let's play with this simplified Dockerfile:
FROM alpine
ENTRYPOINT ["echo", "python", "manage.py"]
CMD ["runserver", '0.0.0.0:8000']
Now build it and run it:
$ docker build .
...
Successfully built 24d598ae4182
$ docker run --rm 24d598ae4182
python manage.py /bin/sh -c ["runserver", '0.0.0.0:8000']
Docker is pretty picky on the JSON-array form of the CMD, ENTRYPOINT, and RUN commands. If something doesn't parse as a JSON array, it will silently fall back to treating it as a plain command, which will get implicitly wrapped in a /bin/sh -c '...' invocation. That's what you're seeing here.
If you edit my Dockerfile to have double quotes in the CMD line and rebuild the image, then you'll see
$ docker run --rm 58114fa1fdb4
python manage.py runserver 0.0.0.0:8000
and if you actually COPY code in, use a Python base image, and delete that debugging echo, that's the command you want to execute.