docker-django-bootstrap

Dockerfile for quickly running Django projects in a Docker container.

Run Django projects from source using Gunicorn and Nginx.

Usage

Step 0: Get your Django project in shape

There are a few ways that your Django project needs to be set up in order to be compatible with this Docker image.

setup.py
Your project must have a setup.py. All dependencies (including Django itself) need to be listed as install_requires.

Static files
Your project's static files must be set up as follows:

STATIC_URL = '/static/'
STATIC_ROOT = BASE_DIR/static or BASE_DIR/staticfiles

Media files
If your project makes use of user-uploaded media files, it must be set up as follows:

MEDIA_URL = '/media/'
MEDIA_ROOT = BASE_DIR/media or BASE_DIR/mediafiles

Note: Any files stored in directories called static, staticfiles, media, or mediafiles in the project root directory will be served by Nginx. Do not store anything here that you do not want the world to see.

Step 1: Write a Dockerfile

In the root of the repo for your Django project, add a Dockerfile for the project. For example, this file could contain:

FROM praekeltfoundation/django-bootstrap
ENV DJANGO_SETTINGS_MODULE "my_django_project.settings"
RUN django-admin collectstatic --noinput
ENV APP_MODULE "my_django_project.wsgi:application"

Let's go through these lines one-by-one:

The FROM instruction here tells us which image to base this image on. We use the django-bootstrap base image.
We set the DJANGO_SETTINGS_MODULE environment variable so that Django knows where to find its settings. This is necessary for any django-admin commands to work.
Optional: If you need to run any build-time tasks, such as collecting static assets, now's the time to do that.
We set the APP_MODULE environment variable that will be passed to gunicorn, which is installed and run in the django-bootstrap base image. gunicorn needs to know which WSGI application to run.

The django-bootstrap base image actually does a few steps automatically using Docker's ONBUILD instruction. It will:

COPY . /app - copies the source of your project into the image
RUN chown -R gunicorn:gunicorn /app - ensures the gunicorn user can write to /app and its subdirectories
RUN pip install -e . - installs your project using pip All these instructions occur directly after the FROM instruction in your Dockerfile.

By default, the django-entrypoint.sh script is run when the container is started. This script runs a once-off django-admin migrate to update the database schemas and then launches nginx and gunicorn to run the application.

This django-entrypoint.sh script also allows you to create a Django super user account if needed. Setting the SUPERUSER_PASSWORD environment variable will result in a Django superuser account being made with the admin username. This will only happen if no admin user exists.

You can skip the execution of this script and run other commands by overriding the CMD instruction. For example, to run a Celery worker, add the following to your Dockerfile:

CMD ["celery", "worker", \
     "--app", "my_django_project", \
     "--loglevel", "info"]

Alternatively, you can override the command at runtime:

docker run my_django_project_image celery worker --app my_django_project --loglevel info

Step 2: Add a `.dockerignore` file

Add a file called .dockerignore to the root of your project. A good start is just to copy in the .dockerignore file from the example Django project in this repo.

This image automatically copies in the entire source of your project, but some of those files probably aren't needed inside the Docker image you're building. We tell Docker about those unneeded files using a .dockerignore file, much like how one would tell Git not to track files using a .gitignore file.

As a general rule, you should list all the files in your .gitignore in your .dockerignore file. If you don't need it in Git, you shouldn't need it in Docker.

Additionally, you shouldn't need any Git stuff inside your Docker image. It's especially important to have Docker ignore the .git directory because every Git operation you perform will result in files changing in that directory (whether you end up in the same state in Git as you were previously or not). This could result in unnecessary invalidation of Docker's cached image layers.

NOTE: Unlike .gitignore files, .dockerignore files do not apply recursively to subdirectories. So, for example, while the entry *.pyc in a .gitignore file will cause Git to ignore ./abc.pyc and ./def/ghi.pyc, in a .dockerignore file, that entry will cause Docker to ignore only ./abc.pyc. This is very unfortunate. In order to get the same behaviour from a .dockerignore file, you need to add an extra leading **/ glob pattern — i.e. **/*.pyc. For more information on the .dockerignore file syntax, see the Docker documentation.

Celery

It's common for Django applications to have Celery workers performing tasks alongside the actual website. In most cases it makes sense to run each Celery process in a container separate from the Django/Gunicorn one, so as to follow the rule of one(-ish) process per container. But in some cases, running a whole bunch of containers for a relatively simple site may be overkill. Additional containers generally have some overhead in terms of CPU and, especially, memory usage.

This image provides the option to run a Celery worker inside the container, alongside Gunicorn/Nginx. To run a Celery worker you must set the CELERY_APP environment variable.

Note that, as with Django, your project needs to specify Celery in its install_requires in order to use Celery. Celery is not installed in this image by default.

Configuration

The following environment variables can be used to configure Celery. A number of these can also be configured via the Django project's settings.

`CELERY_APP`:

Required: yes
Default: none
Celery option: -A/--app

`CELERY_BROKER`:

Required: no
Default: none
Celery option: -b/--broker

`CELERY_LOGLEVEL`:

Required: no
Default: INFO
Celery option: -l/--loglevel

`CELERY_CONCURRENCY`:

Note that by default Celery runs as many worker processes as there are processors. We instead default to 1 worker process here to ensure containers use a consistent and small amount of resources. If you need to run many worker processes, they should be in separate containers.

Required: no
Default: 1
Celery option: -c/--concurrency

`CELERY_BEAT`:

Set this option to any non-empty value to have a Celery beat scheduler process run as well.

Required: no
Default: none
Celery option: n/a

Other configuration

Gunicorn

Gunicorn is run with some basic configuration:

Runs WSGI app defined in APP_MODULE environment variable
Starts workers under the gunicorn user and group
Listens on a Unix socket at /var/run/gunicorn/gunicorn.sock
Access logs can be logged to stderr by setting the GUNICORN_ACCESS_LOGS environment variable to a non-empty value.

Extra settings can be provided by overriding the CMD instruction to pass extra parameters to the entrypoint script. For example:

CMD ["django-entrypoint.sh", "--threads", "5", "--timeout", "50"]

See all the settings available for gunicorn here. A common setting is the number of Gunicorn workers which can be set with the WEB_CONCURRENCY environment variable.

Nginx

Nginx is set up with mostly default config:

Access logs are sent to stdout, error logs to stderr
Listens on port 8000 (and this port is exposed in the Dockerfile)
Serves files from /static/ and /media/
All other requests are proxied to the Gunicorn socket

Generally you shouldn't need to adjust Nginx's settings. If you do, the configuration files of interest are at:

/etc/nginx/nginx.conf: Main configuration
/etc/nginx/conf.d/django.conf: Proxy configuration

License

westerncapelabs/docker-django-bootstrap

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