Is there a way to automatically activate a virtualenv as a docker entrypoint?

Question

I have a flask app inside of a docker container. I would like to use the python package zappa to deploy that app to Amazon Web Services.

Unfortunately zappa requires that it and all of my apps dependencies be installed in a python virtual environment.

So I have rebuilt my docker image and moved everything into a virtual environment in it.

The problem is that now i can't run commands like:

docker exec <container> flask <sub command>

because flask is installed in a virtual environment which has not been activated.

I can still do this:

host$ docker exec -it <container> bash

container$ source venv/bin/activate
container$ flask <sub command>

Also, I can no longer run my default Dockerfile CMD (gunicorn) because that is also is my virtual environment.

Does this make any more sense?

Answer 1

As an alternative to just sourcing the script inline with the command, you could make a script that acts as an ENTRYPOINT. An example entrypoint.sh would look something like:

#!/bin/bash
source venv/bin/activate
exec "$@"

Then in your Dockerfile you would copy this file and set it as the ENTRYPOINT:

FROM myimage
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

Now you can run it like docker run mynewimage flask <sub command> or docker run mynewimage gunicorn.

Answer 2

You don't need to activate the env. Prepend /path/to/virtualenv/bin to $PATH, then python, pip, etc. automatically point to the commands in the virtualenv.

FROM python:3.4-alpine
WORKDIR /deps
ENV PATH=/virtualenv/bin:$PATH
RUN pip install virtualenv && \
    mkdir virtualenv && \
    virtualenv /virtualenv
COPY . /deps

Example working:

#Build dockerfile
docker build . -t="venv_example"
#Run all python commands in virtualenv w/ no hassle
docker run --rm venv_example which python
>/virtualenv/bin/python
docker run --rm venv_example which pip
>/virtualenv/bin/pip

Answer 3

Try:

docker exec <container> sh -c 'source venv/bin/activate; flask <sub command>'

Your command can be:

CMD sh -c 'source venv/bin/activate; gunicorn...'