Deploy Python applications

A Python web application runs on Sevalla as an application: Sevalla builds an image from your Git repository, then runs it as processes. The web process serves HTTP with a production server such as Gunicorn or Uvicorn, background workers run task queues such as Celery, and jobs run migrations before each deployment.

Framework guides

Django

Deploy Django, then add object storage, caching, async views, Celery, health checks and multitenancy.

FastAPI

Deploy FastAPI with SQLModel and Alembic, then add object storage, caching, Celery and health checks.

Flask

Deploy Flask with an application factory, then add caching, Celery and health checks.

Moving from Heroku? See Migrate from Heroku.

How Python applications run on Sevalla

Part	On Sevalla
Build	Nixpacks 1.41 by default. It detects Python from `requirements.txt`, `pyproject.toml`, `Pipfile` or `main.py`, and installs the dependencies into a virtual environment at `/opt/venv`, which is on the `PATH`.
Package managers	pip with `requirements.txt`, Poetry with `poetry.lock`, PDM with `pdm.lock`, uv with `uv.lock`, Pipenv with `Pipfile`
Python version	Set in `.python-version` (for example `3.13`), `runtime.txt` or the `NIXPACKS_PYTHON_VERSION` environment variable. Nixpacks 1.41 supports versions up to 3.13. Pin the version: Django 6.1, for example, needs 3.12 or later.
Web server	A production server such as Gunicorn (WSGI) or Uvicorn (ASGI), listening on `0.0.0.0` and the port in the `PORT` environment variable. Sevalla sets `PORT` to the web process’s port, `8080` by default.
Start command	`[start]` in `nixpacks.toml`, or the Custom start command of a process on the Processes tab. Without either, Nixpacks runs `python manage.py migrate && gunicorn <project>.wsgi` for Django and `python main.py` when there’s a `main.py`.
Migrations	A job with the start policy Before deployment. If it fails, the deployment fails and the previous version keeps running.
Task queues	A background worker, for example `celery -A storefront worker`.
Scheduled tasks	A cron job, for example `python manage.py clearsessions` every night.
Databases	PostgreSQL, MySQL, MariaDB, Redis or Valkey on Sevalla, reached over an internal connection that adds the connection details as environment variables.
Files	The filesystem resets on every deployment. Keep uploads in object storage, or attach a disk.
Other build strategies	Railpack, Buildpacks and Dockerfile, on the application’s Settings tab

See Processes for every process type and its settings.

Connection variables

When you add an internal connection and turn on Add environment variables to the application, Sevalla adds these variables (see Environment variables an internal connection adds). You can rename them in the same sheet before you save, for example DB_URL to DATABASE_URL.

Database	Variables	URL format
PostgreSQL	`DB_HOST`, `DB_PORT`, `DB_DATABASE`, `DB_USERNAME`, `DB_PASSWORD`, `DB_URL`	`postgres://<user>:<password>@<host>:<port>/<database>`
MySQL, MariaDB	The same six variables	`mysql://<user>:<password>@<host>:<port>/<database>`
Redis	`REDIS_HOST`, `REDIS_PORT`, `REDIS_PASSWORD`, `REDIS_URL`	`redis://:<password>@<host>:<port>/0`
Valkey	The same four variables	`valkey://:<password>@<host>:<port>/0`

Two schemes need care in Python:

SQLAlchemy (and so SQLModel, Flask-SQLAlchemy-Lite and Alembic) doesn’t accept postgres://. Replace it with postgresql+psycopg:// in code. Django’s database URL parsers accept it as is.
redis-py, Celery and Django’s Redis cache accept redis://, rediss:// and unix:// only. With a Valkey database, replace valkey:// with redis://.

​Framework guides