Build a rock for a Django app¶

In this tutorial, we’ll create a simple Django app and learn how to containerise it in a rock, using Rockcraft’s django-framework extension.

Setup¶

We recommend starting from a clean Ubuntu installation. If we don’t have one available, we can create one using Multipass:

Is Multipass already installed and active? Check by running

snap services multipass

If we see the multipass service but it isn’t “active”, then we’ll need to run sudo snap start multipass. On the other hand, if we get an error saying snap "multipass" not found, then we must install Multipass:

sudo snap install multipass

Then we can create the VM with the following command:

multipass launch --disk 10G --name rock-dev 24.04

Finally, once the VM is up, open a shell into it:

multipass shell rock-dev

LXD will be required for building the rock. Make sure it is installed and initialised:

sudo snap install lxd
lxd init --auto

In order to create the rock, we’ll install Rockcraft with classic confinement, which grants it access to the whole file system:

sudo snap install rockcraft --classic

We’ll use Docker to run the rock. We can install it as a snap:

sudo snap install docker

By default, Docker is only accessible with root privileges (sudo). We want to be able to use Docker commands as a regular user:

sudo addgroup --system docker
sudo adduser $USER docker
newgrp docker

Restart Docker:

sudo snap disable docker
sudo snap enable docker

Note that we’ll also need a text editor. We can either install one of our choice or simply use one of the already existing editors in the Ubuntu environment (like vi).

Finally, create an empty project directory:

mkdir django-hello-world
cd django-hello-world

Create the Django app¶

Start by creating the “Hello, world” Django app that will be used for this tutorial.

Create a requirements.txt file, copy the following text into it and then save it:

~/django-hello-world/requirements.txt¶

Django>=5.2.1

In order to test the Django app locally (before packing it into a rock), install python3-venv and create a virtual environment:

sudo apt-get update && sudo apt-get install python3-venv -y
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Create a new project using django-admin:

django-admin startproject django_hello_world

Change into the django_hello_world directory and run the Django app using python manage.py runserver to verify that it works.

Test the Django app by using curl to send a request to the root endpoint. We’ll need a new terminal for this – run multipass shell rock-dev to get another terminal:

curl --fail localhost:8000

The Django app should respond with The install worked successfully! Congratulations!.

Note

The response from the Django app includes HTML and CSS which makes it difficult to read on a terminal. Visit http://localhost:8000 using a browser to see the fully rendered page.

The Django app looks good, so let’s stop it for now by pressing Ctrl + C.

Pack the Django app into a rock¶

Now let’s create a container image for our Django app. We’ll use a rock, which is an OCI-compliant container image based on Ubuntu.

First, we’ll need a rockcraft.yaml project file. We’ll take advantage of a pre-defined extension in Rockcraft with the --profile flag that caters initial rock files for specific web app frameworks. Using the Django profile, Rockcraft automates the creation of rockcraft.yaml and tailors the file for a Django app. Change back into the ~/django-hello-world directory and initialize the rock:

cd ..
rockcraft init --profile django-framework

The project file will automatically be created in the working directory as rockcraft.yaml.

Check out the contents of rockcraft.yaml:

cat rockcraft.yaml

The top of the file should look similar to the following snippet:

~/django-hello-world/rockcraft.yaml¶

name: django-hello-world
# see https://documentation.ubuntu.com/rockcraft/en/1.6.0/explanation/bases/
# for more information about bases and using 'bare' bases for chiselled rocks
base: [email protected] # the base environment for this Django app
version: '0.1' # just for humans. Semantic versioning is recommended
summary: A summary of your Django app # 79 char long summary
description: |
    This is django-hello-world's description. You have a paragraph or two to tell the
    most important story about it. Keep it under 100 words though,
    we live in tweetspace and your description wants to look good in the
    container registries out there.
# the platforms this rock should be built on and run on.
# you can check your architecture with `dpkg --print-architecture`
platforms:
    amd64:
    # arm64:
    # ppc64el:
    # s390x:

Verify that the name is django-hello-world.

The platforms key must match the architecture of your host. Check the architecture of your system:

dpkg --print-architecture

Edit the platforms key in rockcraft.yaml if required.

Note

For this tutorial, we’ll use the name django-hello-world and assume we’re running on the amd64 platform. Check the architecture of the system using dpkg --print-architecture.

The name, version and platform all influence the name of the generated .rock file.

Pack the rock:

rockcraft pack

Warning

There is a known connectivity issue with LXD and Docker. If we see a networking issue such as “A network related operation failed in a context of no network access” or Client.Timeout, allow egress network traffic to flow from the LXD managed bridge using:

iptables  -I DOCKER-USER -i <network_bridge> -j ACCEPT
ip6tables -I DOCKER-USER -i <network_bridge> -j ACCEPT
iptables  -I DOCKER-USER -o <network_bridge> -m conntrack \
  --ctstate RELATED,ESTABLISHED -j ACCEPT
ip6tables -I DOCKER-USER -o <network_bridge> -m conntrack \
  --ctstate RELATED,ESTABLISHED -j ACCEPT

Run lxc network list to show the existing LXD managed bridges.

Depending on the network, this step can take a couple of minutes to finish.

Once Rockcraft has finished packing the Django rock, we’ll find a new file in the project’s working directory (an OCI archive) with the .rock extension:

ls *.rock -l --block-size=MB

The created rock is about 75MB in size. We will reduce its size later in this tutorial.

Note

If we changed the name or version in the project file or are not on an amd64 platform, the name of the .rock file will be different.

The size of the rock may vary depending on factors like the architecture we are building on and the packages installed at the time of packing.

Run the Django rock with Docker¶

We already have the rock as an OCI archive. Now we’ll need to load it into Docker. Docker requires rocks to be imported into the daemon since they can’t be run directly like an executable.

Copy the rock:

sudo rockcraft.skopeo copy \
  --insecure-policy \
  oci-archive:django-hello-world_0.1_$(dpkg --print-architecture).rock \
  docker-daemon:django-hello-world:0.1

This command contains the following pieces:

--insecure-policy: adopts a permissive policy that removes the need for a dedicated policy file.
oci-archive: specifies the rock we created for our Django app.
docker-daemon: specifies the name of the image in the Docker registry.

Check that the image was successfully loaded into Docker:

sudo docker images django-hello-world:0.1

The output should list the Django container image, along with its tag, ID and size:

REPOSITORY TAG IMAGE ID CREATED SIZEdjango-hello-world 0.1 5cd019b51db9 6 days ago 184MB

Note

The size of the image reported by Docker is the uncompressed size which is larger than the size of the compressed .rock file.

Now we’re ready to run the rock and test the containerised Django app:

sudo docker run --rm -d -p 8000:8000 \
  --name django-hello-world django-hello-world:0.1

Use the same curl command as before to send a request to the Django app’s root endpoint which is running inside the container:

curl --fail localhost:8000

The Django app should again respond with The install worked successfully! Congratulations!.

View the app logs¶

When deploying the Django rock, we can always get the app logs via Pebble:

sudo docker exec django-hello-world pebble logs django

As a result, Pebble will give us the logs for the django service running inside the container. We should expect to see something similar to this:

2024-08-20T06:34:36.114Z [django] [2024-08-20 06:34:36 +0000] [17] [INFO] Starting gunicorn 23.0.02024-08-20T06:34:36.115Z [django] [2024-08-20 06:34:36 +0000] [17] [INFO] Listening at: http://0.0.0.0:8000 (17)2024-08-20T06:34:36.115Z [django] [2024-08-20 06:34:36 +0000] [17] [INFO] Using worker: sync2024-08-20T06:34:36.116Z [django] [2024-08-20 06:34:36 +0000] [18] [INFO] Booting worker with pid: 18

We can also choose to follow the logs by using the -f option with the pebble logs command above. To stop following the logs, press Ctrl + C.

Cleanup¶

Now we have a fully functional rock for our Django app! This concludes the first part of this tutorial, so we can stop the container and remove the respective image for now:

sudo docker stop django-hello-world
sudo docker rmi django-hello-world:0.1

Chisel the rock¶

This is an optional but recommended step, especially if we’re looking to deploy the rock into a production environment. With Chisel we can produce lean and production-ready rocks by getting rid of all the contents that are not needed for the Django app to run. This results in a much smaller rock with a reduced attack surface.

Note

It is recommended to run chiselled images in production. For development, we may prefer non-chiselled images as they will include additional development tooling (such as for debugging).

The first step towards chiselling the rock is to ensure we are using a bare base. In the project file, change the base to bare and add build-base: ubuntu@22.04:

sed -i \
  "s/base: .*/base: bare\nbuild-base: [email protected]/g" \
  rockcraft.yaml

So that we can compare the size after chiselling, open the project file and change the version (e.g. to 0.1-chiselled). The top of the rockcraft.yaml file should look similar to the following:

~/django-hello-world/rockcraft.yaml¶

name: django-hello-world
# see https://documentation.ubuntu.com/rockcraft/en/1.6.0/explanation/bases/
# for more information about bases and using 'bare' bases for chiselled rocks
base: bare
build-base: [email protected]
version: '0.1-chiselled'
summary: A summary of your Django app # 79 char long summary
description: |
    This is django-hello-world's description. You have a paragraph or two to tell the
    most important story about it. Keep it under 100 words though,
    we live in tweetspace and your description wants to look good in the
    container registries out there.
# the platforms this rock should be built on and run on.
# you can check your architecture with `dpkg --print-architecture`
platforms:
    amd64:
    # arm64:
    # ppc64el:
    # s390x:

Pack the rock with the new bare base:

rockcraft pack

As before, verify that the new rock was created:

ls *.rock -l --block-size=MB

We’ll verify that the new Django rock is now approximately 15% smaller in size! And that’s just because of the simple change of base.

And the functionality is still the same. As before, we can confirm this by running the rock with Docker:

sudo rockcraft.skopeo --insecure-policy \
  copy oci-archive:django-hello-world_0.1-chiselled_$(dpkg --print-architecture).rock \
  docker-daemon:django-hello-world:0.1-chiselled
sudo docker images django-hello-world:0.1-chiselled
sudo docker run --rm -d -p 8000:8000 \
  --name django-hello-world django-hello-world:0.1-chiselled

and then using the same curl request:

curl --fail localhost:8000

The Django app should still respond with The install worked successfully! Congratulations!.

Cleanup¶

And that’s it. We can now stop the container and remove the corresponding image:

sudo docker stop django-hello-world
sudo docker rmi django-hello-world:0.1-chiselled

Update the Django app¶

As a final step, let’s update our app. For example, we want to add a new /time/ endpoint which returns the current time.

cd django_hello_world
django-admin startapp time_app

Open the file time_app/views.py and replace its contents with the following:

~/django-hello-world/django_hello_world/time_app/views.py¶

import datetime

from django.http import HttpResponse

def index(request):
    return HttpResponse(f"{datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')}\n")

Create the file time_app/urls.py with the following contents:

~/django-hello-world/django_hello_world/time_app/urls.py¶

from django.urls import path

from . import views

urlpatterns = [
    path("", views.index, name="index"),
]

Open the file django_hello_world/urls.py and replace its contents with the following:

~/django-hello-world/django_hello_world/django_hello_world/urls.py¶

from django.contrib import admin
from django.urls import include, path

urlpatterns = [
    path("time/", include("time_app.urls")),
    path("admin/", admin.site.urls),
]

Since we are creating a new version of the app, go back to the tutorial root directory using cd .. and open the project file and change the version (e.g. to 0.2). The top of the rockcraft.yaml file should look similar to the following:

~/django-hello-world/rockcraft.yaml¶

name: django-hello-world
# see https://documentation.ubuntu.com/rockcraft/en/1.6.0/explanation/bases/
# for more information about bases and using 'bare' bases for chiselled rocks
base: bare
build-base: [email protected]
version: '0.2'
summary: A summary of your Django app # 79 char long summary
description: |
    This is django-hello-world's description. You have a paragraph or two to tell the
    most important story about it. Keep it under 100 words though,
    we live in tweetspace and your description wants to look good in the
    container registries out there.
# the platforms this rock should be built on and run on.
# you can check your architecture with `dpkg --print-architecture`
platforms:
    amd64:
    # arm64:
    # ppc64el:
    # s390x:

Note

rockcraft pack will create a new image with the updated code even if we don’t change the version. It is recommended to change the version whenever we make changes to the app in the image.

Pack and run the rock using similar commands as before:

rockcraft pack
sudo rockcraft.skopeo --insecure-policy copy \
  oci-archive:django-hello-world_0.2_$(dpkg --print-architecture).rock \
  docker-daemon:django-hello-world:0.2
sudo docker images django-hello-world:0.2
sudo docker run --rm -d -p 8000:8000 \
  --name django-hello-world django-hello-world:0.2

Note

Note that the resulting .rock file will now be named differently, as its new version will be part of the filename.

Finally, use curl to send a request to the /time/ endpoint:

curl --fail localhost:8000/time/

The updated app should respond with the current date and time (e.g. 2024-08-20 07:28:19).

Note

If you are getting a 404 for the /time/ endpoint, check the Troubleshooting steps below.

Cleanup¶

We can now stop the container and remove the corresponding image:

sudo docker stop django-hello-world
sudo docker rmi django-hello-world:0.2

Reset the environment¶

We’ve reached the end of this tutorial.

If we’d like to reset the working environment, we can simply run the following:

# exit and delete the virtual environment
deactivate
rm -rf .venv django_hello_world __pycache__
# delete all the files created during the tutorial
rm django-hello-world_0.1_$(dpkg --print-architecture).rock \
  django-hello-world_0.1-chiselled_$(dpkg --print-architecture).rock \
  django-hello-world_0.2_$(dpkg --print-architecture).rock \
  rockcraft.yaml requirements.txt

We can also clean the Multipass instance up. Start by exiting it:

exit

And then we can proceed with its deletion:

multipass delete rock-dev
multipass purge

Troubleshooting¶

App updates not taking effect?

Upon changing your Django app and re-packing the rock, if you believe your changes are not taking effect (e.g. the /time/ endpoint is returning a 404), try running rockcraft clean and pack the rock again with rockcraft pack.