Travis + Docker result in broken build on CI

What happened?

Try to generate a project with Docker and Tarvis enabled, the tarvis config is not suitable and fails the build:

Build logs

travis_fold:end:install
travis_time:start:183a4568
$ pytest
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/environ/environ.py", line 273, in get_value
    value = self.ENVIRON[var]
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/os.py", line 669, in __getitem__
    raise KeyError(key) from None
KeyError: 'DATABASE_URL'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.6.7/bin/pytest", line 10, in <module>
    sys.exit(main())
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/_pytest/config/__init__.py", line 63, in main
    config = _prepareconfig(args, plugins)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/_pytest/config/__init__.py", line 207, in _prepareconfig
    pluginmanager=pluginmanager, args=args
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/hooks.py", line 289, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/manager.py", line 87, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/manager.py", line 81, in <lambda>
    firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/callers.py", line 203, in _multicall
    gen.send(outcome)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/_pytest/helpconfig.py", line 94, in pytest_cmdline_parse
    config = outcome.get_result()
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/_pytest/config/__init__.py", line 687, in pytest_cmdline_parse
    self.parse(args)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/_pytest/config/__init__.py", line 895, in parse
    self._preparse(args, addopts=addopts)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/_pytest/config/__init__.py", line 851, in _preparse
    early_config=self, args=args, parser=self._parser
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/hooks.py", line 289, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/manager.py", line 87, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/manager.py", line 81, in <lambda>
    firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/callers.py", line 208, in _multicall
    return outcome.get_result()
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pytest_django/plugin.py", line 333, in pytest_load_initial_conftests
    dj_settings.DATABASES
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/django/conf/__init__.py", line 79, in __getattr__
    self._setup(name)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/django/conf/__init__.py", line 66, in _setup
    self._wrapped = Settings(settings_module)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/django/conf/__init__.py", line 157, in __init__
    mod = importlib.import_module(self.SETTINGS_MODULE)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/travis/build/browniebroke/cc-dj-tests/config/settings/test.py", line 5, in <module>
    from .base import *  # noqa
  File "/home/travis/build/browniebroke/cc-dj-tests/config/settings/base.py", line 44, in <module>
    DATABASES = {"default": env.db("DATABASE_URL")}
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/environ/environ.py", line 204, in db_url
    return self.db_url_config(self.get_value(var, default=default), engine=engine)
  File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/environ/environ.py", line 277, in get_value
    raise ImproperlyConfigured(error_msg)
django.core.exceptions.ImproperlyConfigured: Set the DATABASE_URL environment variable
travis_time:end:183a4568:start=1559838789069844257,finish=1559838789825801676,duration=755957419
The command "pytest" exited with 1.



Done. Your build exited with 1.

We should provide a suitable config when Docker is selected with Travis.

How to fix this?

Generate a project with the 2 options enabled, push it to Github with Travis and make the build pass by running the appropriate docker commands instead of bare metals ones.

[step21]

This works with docker-in-docker and probably requires docker to run in privileged mode, and requires an image with docker-compose (see below).

image: docker:latest
services:
  - docker:dind

variables:
  DOCKER_HOST: tcp://docker:2375
  DOCKER_DRIVER: overlay2

stages:
  - build
  - start
  - test
  
build:
  stage: build
  image: tiangolo/docker-with-compose
  script:
    - docker-compose -f local.yml build

start:
  stage: start
  image: tiangolo/docker-with-compose
  script:
    - docker-compose -f local.yml up -d
    - docker-compose -f local.yml down -v

test:
  stage: test
  image: tiangolo/docker-with-compose
  script:
    - docker-compose run django coverage run -m pytest
  allow_failure: true

[wandering-tales]

@Datamance I replied to @step21 question in https://github.com/pydanny/cookiecutter-django/issues/2100#issuecomment-507078188.