Abu Ashraf Masnun: Dockerizing a Django Application

I assume you are already familiar with Docker and it’s use cases. If you haven’t yet started using Docker, I strongly recommend you do soon.

I have a Django application that I want to dockerize it for local development. I am also new to Docker, so everything I do in this post might not be suitable for your production environment. So please do check Docker best practices for production apps. This tutorial is meant to be a basic introduction to Docker. In this post, I am going to use Docker Machine and Docker Compose. You can get them by installing the awesome Docker Toolbox.

Components Breakdown

Before we start, we need to break down our requirements so we can individually build the required components. For my particular application, we need these:

1. Django App Server
2. MySQL Database Server
3. Redis Server

We will build images for these separately so we can create individual containers and link them together to compose our ultimate application. We shall build our Django App server and use pre-built images for MySQL and Redis.

Building the Django App Server

Before we begin, let’s talk Dockerfiles. Dockerfiles are scripts to customize our docker builds. It allows us control and flexibility over how we build the images for our applications. We will use our custom Dockerfile to build the Django app server.

To build an image for a Django application we need to go through these following steps:

• Select a Linux image, we choose Ubuntu
• Install required packages for the distro.
• Install Python packages which are required for the app
• Provide a default command to run and ports to expose

Here’s the Dockerfile we shall use:

FROM phusion/baseimage
MAINTAINER masnun

ENV DEBIAN_FRONTEND noninteractive

RUN apt-get update
RUN apt-get install -y python python-pip python-dev 
RUN apt-get install -y libxml2-dev libxslt-dev libffi-dev libssl-dev 
RUN apt-get install -y libmysqlclient-dev

ADD requirements.txt /app/src/requirements.txt
WORKDIR /app/src
RUN pip install -r requirements.txt

WORKDIR /app/src/lisp
CMD [ "python", "manage.py", "runall"]

EXPOSE 8000

So what are we doing here:

• We’re choosing phusion/baseimage as our base image. It’s a barebone image based on Ubuntu. Ubuntu by default comes with many packages which we don’t need to run inside docker. This base image gets rid of those and provides a very lean and clean image to start with.
• We just provide a Maintainer name
• We set DEBIAN_FRONTEND to be non interactive. This will not display any interactive prompts during the build process. Since the docker build process is automated, we really don’t have any way to interact during it. So we disable interaction. And as you might have guessed already ENV sets an environment variable.
• We install some packages we shall need.
• We copy our requirements.txt file to /app/src/requirements.txt, change the work directory and install the packages using pip. ADD is used to copy any files or directories to the container while it builds. You might wonder why we didn’t copy over our entire project – that’s because we want to use docker for our development. We will use a nice featire of Docker which would allow us to mount our local directories directly inside the container. Doing this, we would not need to copy files every time they change. More on this will come later.
• We change directory to /app/src/lisp and run the runall management command. This command runs the Django default server along with some other services my application needs. But usually we would want to just do runserver
• We EXPOSE port 8000

If you go through the Dockerfile References you will notice – we can do a lot more with Dockerfiles.

Docker Compose and Linking Services

As we mentioned earlier, we shall use pre-built images for MySQL and Redis. We could build them ourselves too but why not take advantage of the well maintained images from the generous folks in the docker community?

We can link multiple docker containers to compose a final application. We can do that using the docker command manually. But Docker Compose is a very nice tool which allows us to define the services we need in a very easy to read syntax. With docker compose, we don’t need to run them manually, we can just use simple commands to do complex docker magic! Here’s our docker-compose.yml file:

web:
  build: .
  restart: always
  volumes:
    - .:/app/src
  ports:
    - "8000:8000"
  links:
    - redis
    - mysql

redis:
  image: redis:latest
  volumes:
    - /var/lib/redis
  ports:
    - "6379"

mysql:
  image: mysql:latest
  volumes:
    - /var/lib/mysql
  ports:
    - "3306:3306"
  environment:
    MYSQL_ROOT_PASSWORD: su53RsEc53T!

In our docker-compose file, we define 3 components:

• For the web, we pass the path to Dockerfile to build key. We ask to restart always and define volumes to mount. .:/app/src means – mount the current directory on my OS X as /app/src/ on the container. We also define which ports to expose and which containers should be linked with it
• We also define the mysql and redis components with respective configurations. Note that we define the pre-built image name in the image key. Please make sure the volume paths exist and are accessible.

You can consult the Compose File Reference for more details.

Running The Services

To run the application, we can do:

docker-compose up

Please note, the Django server might throw errors if the MySQL / Redis server takes time to initialize. So I usually run them separately:

docker-compose start mysql
docker-compose start redis

# After some time

docker-compose start web

Database Configuration for Django

Our MySQL server is running on the IP of the Docker Machine. You need to use this IP address in your Django settings file. To get the IP of a docker machine, type in:

# Here `default` is the machine name
docker-machine ip default

Creating Initial Databases

We can pass a MYSQL_DATABASE environment value to the mysql image so the database is created when creating the service. Or we can also connect to the docker machine manually and create our databases.