Improve Dockerfile in the new project template (#5800)

* Improve Dockerfile in project template

This reorganises Dockerfile to make it adhere to more common-sense rules,
while not being too opinionated on the deployment process.

* Add dockerignore file

* Make Dockerfile comments nicer

* Delete dockerignore created in a wrong path

* Add the right dockerignore files

* Use slim buster Docker image

* Add sqlite3 files to dockerignore

* Fix Docker image name

wagtail/project_template/.dockerignore

@@ -0,0 +1,39 @@
+# Django project
+/media/
+/static/
+*.sqlite3
+
+# Python and others
+__pycache__
+*.pyc
+.DS_Store
+*.swp
+/venv/
+/tmp/
+/.vagrant/
+/Vagrantfile.local
+node_modules/
+/npm-debug.log
+/.idea/
+.vscode
+coverage
+.python-version
+
+# Distribution / packaging
+.Python
+env/
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg

wagtail/project_template/Dockerfile

@@ -1,27 +1,60 @@
-# Use an official Python runtime as a parent image
-FROM python:3.7
-LABEL maintainer="hello@wagtail.io"
-
-# Set environment varibles
-ENV PYTHONUNBUFFERED 1
-ENV DJANGO_ENV dev
-
-COPY ./requirements.txt /code/requirements.txt
-RUN pip install --upgrade pip
-# Install any needed packages specified in requirements.txt
-RUN pip install -r /code/requirements.txt
-RUN pip install gunicorn
-
-# Copy the current directory contents into the container at /code/
-COPY . /code/
-# Set the working directory to /code/
-WORKDIR /code/
-
-RUN python manage.py migrate
+# Use an official Python runtime based on Debian 10 "buster" as a parent image.
+FROM python:3.8.1-slim-buster
 
+# Add user that will be used in the container.
 RUN useradd wagtail
-RUN chown -R wagtail /code
+
+# Port used by this container to serve HTTP.
+EXPOSE 8000
+
+# Set environment variables.
+# 1. Force Python stdout and stderr streams to be unbuffered.
+# 2. Set PORT variable that is used by Gunicorn. This should match "EXPOSE"
+#    command.
+ENV PYTHONUNBUFFERED=1 \
+    PORT=8000
+
+# Install system packages required by Wagtail and Django.
+RUN apt-get update --yes --quiet && apt-get install --yes --quiet --no-install-recommends \
+    build-essential \
+    libpq-dev \
+    libmariadbclient-dev \
+    libjpeg62-turbo-dev \
+    zlib1g-dev \
+    libwebp-dev \
+ && rm -rf /var/lib/apt/lists/*
+
+# Install the application server.
+RUN pip install "gunicorn==20.0.4"
+
+# Install the project requirements.
+COPY requirements.txt /
+RUN pip install -r /requirements.txt
+
+# Use /app folder as a directory where the source code is stored.
+WORKDIR /app
+
+# Set this directory to be owned by the "wagtail" user. This Wagtail project
+# uses SQLite, the folder needs to be owned by the user that
+# will be writing to the database file.
+RUN chown wagtail:wagtail /app
+
+# Copy the source code of the project into the container.
+COPY --chown=wagtail:wagtail . .
+
+# Use user "wagtail" to run the build commands below and the server itself.
 USER wagtail
 
-EXPOSE 8000
-CMD exec gunicorn {{ project_name }}.wsgi:application --bind 0.0.0.0:8000 --workers 3
+# Collect static files.
+RUN python manage.py collectstatic --noinput --clear
+
+# Runtime command that executes when "docker run" is called, it does the
+# following:
+#   1. Migrate the database.
+#   2. Start the application server.
+# WARNING:
+#   Migrating database at the same time as starting the server IS NOT THE BEST
+#   PRACTICE. The database should be migrated manually or using the release
+#   phase facilities of your hosting platform. This is used only so the
+#   Wagtail instance can be started with a simple "docker run" command.
+CMD set -xe; python manage.py migrate --noinput; gunicorn {{ project_name }}.wsgi:application