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FastAPI Project - Development

Docker Compose

Start the local stack with Docker Compose:

docker compose watch

Now you can open your browser and interact with these URLs:

Frontend, built with Docker, with routes handled based on the path: http://localhost:5173

Backend, JSON based web API based on OpenAPI: http://localhost:8000

Automatic interactive documentation with Swagger UI (from the OpenAPI backend): http://localhost:8000/docs

Adminer, database web administration: http://localhost:8080

Traefik UI, to see how the routes are being handled by the proxy: http://localhost:8090

Note: The first time you start your stack, it might take a minute for it to be ready. While the backend waits for the database to be ready and configures everything. You can check the logs to monitor it.

To check the logs, run (in another terminal):

docker compose logs

To check the logs of a specific service, add the name of the service, e.g.:

docker compose logs backend

Mailcatcher

Mailcatcher is a simple SMTP server that catches all emails sent by the backend during local development. Instead of sending real emails, they are captured and displayed in a web interface.

This is useful for:

Testing email functionality during development
Verifying email content and formatting
Debugging email-related functionality without sending real emails

The backend is automatically configured to use Mailcatcher when running with Docker Compose locally (SMTP on port 1025). All captured emails can be viewed at http://localhost:1080.

Local Development

The Docker Compose files are configured so that each of the services is available in a different port in localhost.

For the backend and frontend, they use the same port that would be used by their local development server, so, the backend is at http://localhost:8000 and the frontend at http://localhost:5173.

This way, you could turn off a Docker Compose service and start its local development service, and everything would keep working, because it all uses the same ports.

For example, you can stop that frontend service in the Docker Compose, in another terminal, run:

docker compose stop frontend

And then start the local frontend development server:

bun run dev

Or you could stop the backend Docker Compose service:

docker compose stop backend

And then you can run the local development server for the backend:

cd backend
fastapi dev app/main.py

Docker Compose in `localhost.tiangolo.com`

When you start the Docker Compose stack, it uses localhost by default, with different ports for each service (backend, frontend, adminer, etc).

When you deploy it to production (or staging), it will deploy each service in a different subdomain, like api.example.com for the backend and dashboard.example.com for the frontend.

In the guide about deployment you can read about Traefik, the configured proxy. That’s the component in charge of transmitting traffic to each service based on the subdomain.

If you want to test that it’s all working locally, you can edit the local .env file, and change:

DOMAIN=localhost.tiangolo.com

That will be used by the Docker Compose files to configure the base domain for the services.

Traefik will use this to transmit traffic at api.localhost.tiangolo.com to the backend, and traffic at dashboard.localhost.tiangolo.com to the frontend.

The domain localhost.tiangolo.com is a special domain that is configured (with all its subdomains) to point to 127.0.0.1. This way you can use that for your local development.

After you update it, run again:

docker compose watch

When deploying, for example in production, the main Traefik is configured outside of the Docker Compose files. For local development, there’s an included Traefik in compose.override.yml, just to let you test that the domains work as expected, for example with api.localhost.tiangolo.com and dashboard.localhost.tiangolo.com.

Docker Compose files and env vars

There is a main compose.yml file with all the configurations that apply to the whole stack, it is used automatically by docker compose.

And there’s also a compose.override.yml with overrides for development, for example to mount the source code as a volume. It is used automatically by docker compose to apply overrides on top of compose.yml.

These Docker Compose files use the .env file containing configurations to be injected as environment variables in the containers.

They also use some additional configurations taken from environment variables set in the scripts before calling the docker compose command.

After changing variables, make sure you restart the stack:

docker compose watch

The .env file

The .env file is the one that contains all your configurations, generated keys and passwords, etc.

Depending on your workflow, you could want to exclude it from Git, for example if your project is public. In that case, you would have to make sure to set up a way for your CI tools to obtain it while building or deploying your project.

One way to do it could be to add each environment variable to your CI/CD system, and updating the compose.yml file to read that specific env var instead of reading the .env file.

Pre-commits and code linting

we are using a tool called prek (modern alternative to Pre-commit) for code linting and formatting.

When you install it, it runs right before making a commit in git. This way it ensures that the code is consistent and formatted even before it is committed.

You can find a file .pre-commit-config.yaml with configurations at the root of the project.

Install prek to run automatically

prek is already part of the dependencies of the project.

After having the prek tool installed and available, you need to “install” it in the local repository, so that it runs automatically before each commit.

Using uv, you could do it with (make sure you are inside backend folder):

❯ uv run prek install -f
prek installed at `../.git/hooks/pre-commit`

The -f flag forces the installation, in case there was already a pre-commit hook previously installed.

Now whenever you try to commit, e.g. with:

git commit

…prek will run and check and format the code you are about to commit, and will ask you to add that code (stage it) with git again before committing.

Then you can git add the modified/fixed files again and now you can commit.

Running prek hooks manually

you can also run prek manually on all the files, you can do it using uv with:

❯ uv run prek run --all-files
check for added large files..............................................Passed
check toml...............................................................Passed
check yaml...............................................................Passed
fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed
ruff.....................................................................Passed
ruff-format..............................................................Passed
biome check..............................................................Passed