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How To Dockerize A Simple Django App

How To Dockerize A Simple Django App

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Nextwebb
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6 min read

Introduction

According to Docker docs, Docker is a tool that provides OS-level virtualization to deliver software in packages called containers.

Docker made application containers easy to use by providing a simplified, opinionated wrapper around existing Linux distribution invoked as containers, process control, security, and resource management technologies.

Docker excels in these two key areas:

  • Packaging applications
  • Process isolation and management

Docker helps you package and run applications inside isolated little boxes with all platform and application dependencies provided, thus keeping the hosting computer nice and tidy.

Docker solves problems associated with :

  • Missing or incorrect application dependencies such as libraries, interpreters, code/binaries, users, Os packages, etc
  • Conflicts between programs running on the same host machine such as library dependencies or ports; Example: local Django trying to use port 80
  • Insufficient system resources required to run an application such as CPU and memory.

Let’s see how Docker delivers on its promise to “Build, Ship, and Run” applications easily 😃.

Assumptions: We'll be working with a Django application, Some experience working with a Django application might be needed and you have Docker & Docker Compose installed.

Packaging an Application Into An Image

This OS-level virtualization provided by Docker helps us mirror the application and platform into a docker file. The docker file should be placed at the root of the Django project.

# The first instruction is what image we want to base our container on
# We Use an official Python runtime as a parent image
FROM python:3.8.5 as production

# The environment variable ensures that the python output is set straight
# to the terminal without buffering it first
ENV PYTHONUNBUFFERED 1

# create a root directory for our project in the container
RUN mkdir /app

# Set the working directory to /app
WORKDIR /app

# Copy the current directory contents into the container at /app
COPY . /app/

# Install any needed packages specified in requirements.txt
RUN pip install -r requirements.txt

# tell the port number the container should expose
EXPOSE 8000

Docker images also allow you to define metadata and define more options to help operators run the application according to your application needs.

Setting Up A Docker-compose.yml File

For clarity, Docker Compose solves the problem of running multi-container applications at once. You thus can set the desired amount of containers counts, their builds, services, and volumes, and then with a single set of commands, you can build, run, and configure all the containers.

According to Docker-compose Docs Using Compose is basically a three-step process:

  • Define your app’s environment with a Dockerfile so it can be reproduced anywhere.

  • Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.

  • Run docker-compose up and Compose starts and runs your entire app.

it is also located in the root directory of the Django application. The Docker environment variable file .env is necessary when you're creating complex containers or Database service for deployments.

So let's say you have your .env file (that's the full name of the file, by the way) located in the same directory that houses your docker-compose.yml file. In the .env file, you have on these lines: 

DATABASE_NAME=postgresdb
DATABASE_USER=postgresuser
DATABASE_PASSWORD=postgresuser
DATABASE_HOST=db
DATABASE_ENGINE=django.db.backends.postgresql
DATABASE_PORT=5432

A simple docker-compose.yml looks like this:

version: '3.8'

# This file defines two services: The db service and the web service.
services:
  db:
    image: postgres
    environment:
# key-value pair for the environmental variable
      - environment:
        - "POSTGRES_USER:${DATABASE_USER}"
        - "POSTGRES_DB:${DATABASE_NAME}"
        - "POSTGRES_PASSWORD:${DATABASE_PASSWORD}"
        - "POSTGRES_HOST:${DATABASE_HOST}"
    volumes:
# no data is lost  when we stop running the container, only for development
      - ./pgdata:/var/lib/postgresql/data
    ports:
# exposing port 5432 to the host machine
      - "5432:5432"
  web:
    build: .
    command: > 
        bash -c "
        python manage.py makemigrations
        && python manage.py migrate 
        && python manage.py runserver 0.0.0.0:8000
        "
    image: appserver
# for development purposes, so when we make changes to the source code the change gets saved to the container.
    volumes:
      - .:/appserver
    depends_on:
      - db
    ports:
# expose port 8001 to the host machine
      - "8001:8000"

We're all set now, lets build and run our container using this simple command :

docker-compose up

That’s a simple introduction to how application containers can help your team solve many common packaging, distribution, and operational problems; while helping you ship better software 🤓.

Thanks for the audience and I hope you found this article helpful 🤗. Feel free to reach out to me on Github, Twitter and LinkedIn. Do drop a like, comment, and share 😌.

Further Reading

Dockercontainersdocker images