In this section we will build the new application you’ve created in the local development environment; that is, we will set it up on your own computer.
Obtain the application’s slug (its unique ID) from the Dashboard:
Alternatively you can use the
divio command to list your cloud applications, which will show their slugs:
divio app list
2.1. Build the application locally#
divio app setup command (for example if your application slug is
divio app setup tutorial-project
The Divio CLI will execute a number of steps - this may take a few minutes, depending on how much needs to be downloaded and processed. The Divio CLI tool will build your application locally (see The deployment process for a more detailed description of what’s happening here). Note that depending on the application, you won’t necessarily see all the intermediate steps here:
Creating workspace cloning application repository [...] downloading remote docker images [...] building local docker images [...] creating new database container [...] syncing and migrating database [...] Your workspace is setup and ready to start.
As well as cloning the repository and attempting to build the application, the
setup command will add a
directory containing some Divio-related configuration that connects it to the Control Panel.
cd into the newly-created application directory, where you will find your application code.
2.2. Install Python and Django using the
This application requires that we have Python installed in the container. By using an official Docker base image that
includes Python, we can speed up build times and rely on a lightweight and expertly-constructed foundation. The
Dockerfile that defines the application is currently empty. We will use Python 3.8, so add:
This will use the official Docker
python base image as the foundation for everything else that we build on top.
Let’s check that Docker can build an image from our newly-created Dockerfile, by running:
docker build .
This application will use Django 3.1.x. We can install Django and its Python dependencies by using
pip to process a
list of requirements. Create a new file
requirements.txt in the application and list Django:
The requirements file needs to be made accessible inside the Docker application. So, we will copy it (and everything
else in the root of this application) into the image’s filesystem at
/app (it doesn’t need to be there in
/app is a useful convention), and for convenience, we can set Docker to use
/app as its base
directory. Finally, we will run the
FROM python:3.8 WORKDIR /app COPY . /app RUN pip install -r requirements.txt
Check again that the application builds as expected with
docker build ..
2.3. Create a
docker-compose.yml file for convenience#
docker command is concerned merely with images and containers - not applications as a whole. An application
will typically include a number of components and resources, such as a database and media storage as well as code, and
all these various parts need to be orchestrated to function as an application. Docker Compose provides a very
convenient way to manage and interact with Docker applications. For example, it’s convenient to have port-mapping set
up locally, and to have direct access to files inside the container while developing.
docker-compose.yml configures Docker Compose. Create a new
docker-compose.yml file in the application:
version: "2" services: web: # the application's web service (container) will use an image based on our Dockerfile build: "." # map the internal port 80 to port 8000 on the host ports: - "8000:80" # map the host directory to app (which allows us to see and edit files inside the container) volumes: - ".:/app:rw" # the default command to run whenever the container is launched command: python manage.py runserver 0.0.0.0:80
This now provides a convenient way to run commands inside the Dockerised environment, and also gives us access to a
number of useful
docker-compose commands. For example, now you can use
docker-compose build to build the entire
application, not just one image, and to run commands inside the application. Try
docker-compose build now.
2.4. Create a new Django application in the application#
Next we need to create a new Django application in the application (with
django-admin startproject), so run:
docker-compose run web django-admin startproject myapp .
This starts up a container (
web, which according to
docker-compose.yml will be based on the
the same directory) and executes the
django-admin command inside it. It’s important to note that the command is
executed inside the Docker application environment, and not in the host environment.
The command will add a new
myapp directory and a
manage.py file. Although they were created inside the
container, so you wouldn’t normally be able to see them, the
volumes directive in the
/app to the host filesystem, so you can see them and edit them without having to be inside the Docker
2.5. Start the local application#
Start the application by running
docker-compose up in the terminal:
➜ docker-compose up Starting tutorial-project_web_1 ... done Attaching to tutorial-project_web_1 web_1 | Watching for file changes with StatReloader
Open the application in your web browser by visiting http://127.0.0.1:8000, where you should see the default Django success page.
Notice above that although the Django runserver is running on port 80, the application is accessible on port 8000. The
docker-compose.yml configuration file is responsible for this port-mapping.
If you amend or even just save any Python file in the Django project, the runserver will reload the Python modules and restart.
2.6. Add a start-up instruction to the
Docker Compose is only used locally, not in our cloud deployments. Moreover, the Django runserver that we’re using here is fine for local development but unsuitable for use in production. For production, we will use uWSGI (uWSGI is a WSGI gateway server for Python).
requirements.txt. These dependencies are baked into the image, so every time you amend the requirements, you
will need to rebuild with the new dependency list (we’ll do that in a moment).
The Django application can be started with uWSGI. This should be baked into the
Dockerfile itself, as a start-up
command. To the end of the file, add:
CMD uwsgi --module=myapp.wsgi --http=0.0.0.0:80
once more. Now when the web container is launched it will run the command automatically, to start it up in - for example - a cloud deployment.
However, when we start it locally with
docker-compose up, the
command line in the
overrides that, and uses
python manage.py runserver 0.0.0.0:80 instead.
Try running the application locally using uWSGI rather than the runserver, by temporarily commenting out the
line in the
docker-compose.yml file. Note that it’s not necessary to rebuild after making changes to
docker-compose.yml - Docker Compose uses images, but doesn’t affect what’s in them.
command line in the
docker-compose.yml file before continuing.
2.7. Local commands#
So far, we have used the
docker commands. It’s good to have a basic familiarity
with them and what they do. As you proceed through this tutorial, you may encounter the occasional issue. These
commands will help you when this happens.
divio command is used mainly to manage your local application’s resources and to interact with our Control Panel.
You have already used
divio app setup and
divio app list; you can also use it to do things like push
and pull database and media content. Try:
divio app dashboard
See the Divio CLI reference for more.
docker command is mostly used to manage Docker processes, images and containers (rather than applications as a
whole) and Docker itself. You will rarely need to use it, but it can be useful when you need to understand what Docker
is doing on your machine, or for certain operations.
For example, if you have your application running locally (with
docker-compose up) open a new terminal window to run:
This will show you the Docker processes that are running - you will see something like this (note that the details will differ depending on what you actually have running):
➜ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAME d6007edbaf32 tutorialproject_web "/tini -g -- pytho..." 17 minutes ago Up 8 seconds 0.0.0.0:8000->80/tcp tutorialproject_web_ 27ff3e661027 postgres:13.5 "docker-entrypoint..." 17 minutes ago Up 8 seconds 5432/tcp tutorialproject_db_
In this example, the first container is an instance of the image that you built (when deployed, a similar container will be running in a cloud environment). The second shown here is a Postgres database, running in its own Docker container.
You have already used
docker ps. Try:
docker-compose command is used mainly to control and interact with your local application. You will mostly use
it to start the local application and open a shell in the local web container. You have already used
Just for example, try:
docker-compose run web python manage.py shell
which will open a Django shell in the
You have now set up an application in the local environment, and launched it. The next step is to do some further development work in the application, test it, and deploy it to the cloud.