A GitLab CI workflow inspired by: https://www.digitalocean.com/community/tutorials/how-to-build-docker-images-and-host-a-docker-image-repository-with-gitlab

.gitlab-ci.yml

image: docker:latest

services:
  - docker:dind
  - postgres:latest

stages:
  - build
  - test
  - release

variables:
  PYTHONDONTWRITEBYTECODE: 1
  PYTHONUNBUFFERED: 1
  RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest
  TEST_IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME

before_script:
  - docker version
  - docker info
  - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY

build:
  stage: build
  script:
    - docker pull $CI_REGISTRY_IMAGE:latest || true
    - docker build -f .docker/Dockerfile --cache-from $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA --tag $TEST_IMAGE .
    # - docker build -f .docker/Dockerfile --pull -t $TEST_IMAGE .
    - docker push $TEST_IMAGE

test:
  stage: test
  variables:
    DATABASE_URL: "postgres://postgres@postgres/postgres"
    POSTGRES_DB: postgres
    POSTGRES_PASSWORD: ""
    POSTGRES_USER: postgres
  script:
    - docker run -d -e POSTGRES_DB -e POSTGRES_USER -e POSTGRES_PASSWORD --name postgres postgres:10
    - docker pull $TEST_IMAGE
    - docker run -e DATABASE_URL --link postgres $TEST_IMAGE pytest

release:
  stage: release
  script:
    - docker pull $TEST_IMAGE
    - docker tag $TEST_IMAGE $RELEASE_IMAGE
    - docker push $RELEASE_IMAGE
  only:
    - master

Dockerfile

FROM python:3.7-stretch

ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1

COPY requirements.txt /src/

RUN set -ex && \
    pip install --no-cache-dir \
        -r /src/requirements.txt && \
    rm -rf /root/.cache

COPY . /src/

WORKDIR /src/

ENTRYPOINT ["/src/docker-entrypoint.sh", "--"]

entrypoint.sh

#!/usr/bin/env bash
set -eo pipefail

python manage.py migrate --noinput
python manage.py collectstatic --noinput

exec "$@"