Couldn't import django in docker image on GitLab CI

Question

I tried running my django tests python manage.py test in gitlab ci. Therefore I'm using a docker image. The docker image builds fine, but when it runs the tests on gitlab i get ImportError: No module named 'django' and

Couldn't import Django. Are you sure it's installed and available on your PYTHONPATH environment variable? Did you forget to activate a virtual environment?

See my .gitlab-ci.yml

image: registry.gitlab.com/app/core:latest
services:
    - postgres:latest
stages:
  - test

variables:
    SECRET_KEY: test-secret
    POSTGRES_DB: ...
    POSTGRES_USER: ...
    POSTGRES_PASSWORD: ...

python_tests:
    stage: test
    before_script:
        - export DATABASE_NAME=...
        - export DATABASE_USER=...
        - export DATABASE_PASSWORD=...
        - export DATABASE_HOST=postgres
        - source /app/venv/bin/activate
    script:
        - python manage.py test

and Dockerfile

FROM ubuntu:16.04

RUN apt-get update -y -qq
RUN apt-get install -y -qq build-essential libffi-dev libpq-dev libfontconfig1
RUN apt-get install -y -qq python3 python3-dev python3-pip
RUN apt-get install -y -qq libpq-dev
RUN apt-get install -y -qq nodejs npm

WORKDIR /app

# pip
COPY requirements.txt /app
RUN pip3 install --upgrade pip
RUN pip3 install virtualenv
RUN virtualenv --no-site-packages venv
RUN . venv/bin/activate
RUN pip3 install -r /app/requirements.txt

# npm
RUN ln -s `which nodejs` /usr/bin/node
COPY web/vueapp/package.json /app
RUN npm install

Answer 1

Well you have a issue in your approach. Consider your below RUN statements in Dockerfile

RUN . venv/bin/activate
RUN pip3 install -r /app/requirements.txt

Both above statements are like open two terminals, in one execute . venv/bin/activate . venv/bin/activate and in one pip3 install -r /app/requirements.txt

So your environment gets activated and you let it close and then the next pip3 statement installs on global packages. So change your code to below

RUN . venv/bin/activate && pip3 install -r /app/requirements.txt

When you script is running your are activate the environment and then running python manager.py inside the virtual environment which is blank with no packages. So above change should fix that issue for you