Python: FastAPI, Django, Flask

Python projects have no Dockerfile-free framework detection in the Fjordrun builder; they fall back to Nixpacks, which detects Python from requirements.txt, pyproject.toml (pip, Poetry, PDM, uv), Pipfile or setup.py and installs the dependencies. The build log shows Fjordrun builder: ... building with Nixpacks.

For full control, add a Dockerfile instead.

Two rules

1. Set a start command in Settings → Deploy (or add a Procfile with a web: line, which Nixpacks reads).
2. Listen on 0.0.0.0:$PORT. Fjordrun sets PORT (8080 by default for web services).

FastAPI

requirements.txt:

fastapi
uvicorn[standard]

Start command:

uvicorn main:app --host 0.0.0.0 --port $PORT

For several workers: gunicorn main:app -k uvicorn.workers.UvicornWorker -b 0.0.0.0:$PORT -w 2 (add gunicorn to the requirements).

Django

requirements.txt with django, gunicorn and your database driver (psycopg[binary] for PostgreSQL).

Start command (mysite is your project package):

python manage.py migrate && gunicorn mysite.wsgi --bind 0.0.0.0:$PORT

Settings to check:

import os
ALLOWED_HOSTS = os.environ.get("ALLOWED_HOSTS", "").split(",")
CSRF_TRUSTED_ORIGINS = [f"https://{h}" for h in ALLOWED_HOSTS if h]
SECRET_KEY = os.environ["SECRET_KEY"]
DEBUG = False

Variables:

ALLOWED_HOSTS=${{FJORDRUN_PUBLIC_DOMAIN}}
SECRET_KEY=${{secret(50)}}
DATABASE_URL=${{Postgres.DATABASE_URL}}

${{secret(50)}} is replaced once by a random 50-character value when you save it. To read DATABASE_URL, use dj-database-url or parse it yourself.

Static files: serve them with WhiteNoise and run collectstatic in the build, for example with the custom build command python manage.py collectstatic --noinput.

Flask

gunicorn app:app --bind 0.0.0.0:$PORT

(app:app is module:variable; add gunicorn to the requirements.) Do not use flask run in production.

Python version

Nixpacks reads .python-version or runtime.txt. Service variables are not available during Nixpacks builds, only at runtime; see Build variables.

Using a Dockerfile

FROM python:3.13-slim
WORKDIR /app
ENV PYTHONDONTWRITEBYTECODE=1 PYTHONUNBUFFERED=1
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
RUN useradd -m app && chown -R app /app
USER app
ENV PORT=8080
CMD ["sh", "-c", "uvicorn main:app --host 0.0.0.0 --port ${PORT}"]

Workers and cron jobs

A Celery or RQ worker is a second service from the same repository with kind worker and a start command such as celery -A mysite worker -l info. Scheduled jobs can be a cron service with a schedule and a start command such as python manage.py clearsessions.