Using Docker in Development#

Pegasus optionally includes support for Docker during development. The Docker development setup can also be used as a foundation for deploying to containerized platforms. See our deployment page for more details.

Prerequisites#

You need to install Docker prior to setting up your environment.

Mac users have reported better performance on Docker using OrbStack, which is a Docker Desktop alternative optimized for performance.

Windows users may also need to install a 3rd-party package to run make commands. The easiest way to do that is via these instructions.

Getting Started#

First set up your Pegasus project with Docker enabled and using Postgres as a database following the getting started guide.

Enter the project directory#

cd {{ project_name }}

Run the initialization script#

make init

This will spin up a database, web worker, celery worker, and Redis broker and create and run your database migrations.

Note: users of older versions of Windows may need to install “make” separately to use it. Alternatively, you can just inspect the Makefile in the repository and run the commands manually (e.g. docker compose up -d).

Load server#

Visit http://localhost:8000/ in a browser and you should be up and running!

Using the Makefile#

Pegasus ships with a self-documenting Makefile that will run common commands for you, including starting your containers, performing database operations, and building your front end.

You can run make to list helper functions, and you can view the source of the Makefile file in case you need to add to it or run any once-off commands.

For example, you can run management commands in containers using the same method used in the Makefile. E.g.

docker compose exec web python manage.py createsuperuser

Architecture and how it works#

Containers#

The Docker configuration is primarily in docker-compose.yml.

There are four containers that start: a Postgres database, a Redis instance (for caching and use as a Celery broker), a web container running your Django process, and a Celery container for background jobs.

Settings#

The docker environment sets environment variables using the included .env file.

The .env file is automatically ignored by git, so you can put any additional secrets there. It generally should not be checked into source control. You can instead add variables to .env.example to show what should be included.

Python environments#

The Python environment is run in the containers, which means you do not need to have your own local environment if you are always using Docker for development. Python requirements are automatically installed when the container builds.

However, keep in mind that if you go this route, you will need to run all commands inside the containers as per the instructions below.

Running once-off management commands#

Running commands on the server can be done using docker compose, by following the pattern used in the Makefile.

For example, to bootstrap Stripe subscriptions, run:

docker compose exec web python manage.py bootstrap_subscriptions

Or to promote a user to superuser, run:

docker compose exec web python manage.py promote_user_to_superuser me@example.com

You can also use the make manage command, passing in ARGS like so:

make manage ARGS='promote_user_to_superuser me@example.com'

You can add any commonly used commands you want to custom.mk for convenience.

Updating Python packages#

If you add or modify anything in your requirements.in (and requirements.txt) files, you will have to rebuild your containers.

The easiest way to add new packages is to add them to requirements.in and then run:

make requirements

Which will rebuild your requirements.txt file, rebuild your Docker containers, and then restart your app with the latest dependencies.

Debugging#

You can use debug tools like pdb or ipdb by enabling service ports.

This can be done by running your web container with the following:

docker compose run --service-ports web

If you want to set up debugging with PyCharm, it’s recommended to follow this guide on the topic.

Troubleshooting#

“No such file or directory” errors#

Some environments—especially on Windows—can have trouble finding the files on your local machine. This will often show up as an error like this when starting your app:

python: can't open file '/code/manage.py': [Errno 2] No such file or directory

These issues are usually related to your disk setup. For example, mounting your code on a remote filesystem or external drive to your machine. To fix, try running the code on the same drive where Docker Desktop is installed, or on your machine’s default “C:” drive.

You can also get around this issue by running your application natively, instead of with Docker.

Other Resources#