Activate python virtualenv in Dockerfile

Question

I have a Dockerfile where I try to activate python virtualenv after what, it should install all dependencies within this env. However, everything still gets installed global

Answer 1

Setting this variables

ENV VIRTUAL_ENV /env
ENV PATH /env/bin:$PATH

is not exactly the same as just running

RUN . env/bin/activate

because activation inside single RUN will not affect any lines below that RUN in Dockerfile. But setting environment variables through ENV will activate your virtual environment for all RUN commands.

Look at this example:

RUN virtualenv env                       # setup env
RUN which python                         # -> /usr/bin/python
RUN . /env/bin/activate && which python  # -> /env/bin/python
RUN which python                         # -> /usr/bin/python

So if you really need to activate virtualenv for the whole Dockerfile you need to do something like this:

RUN virtualenv env
ENV VIRTUAL_ENV /env                     # activating environment
ENV PATH /env/bin:$PATH                  # activating environment
RUN which python                         # -> /env/bin/python