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Flask

The Wodby Flask catalog stack runs a Python (Flask) app service with optional PostgreSQL, Valkey, Mailpit, OpenSMTPD, Gotenberg, and Cloud PostgreSQL services. The current services and defaults are documented in wodby/stack-flask.

Create the environment

Start from the Flask boilerplate, or connect your own compatible source repository. The app service is the only required service. The others are optional and not selected by default, so select the ones your application uses when you create the environment. The app service links to PostgreSQL for the database, Valkey for Redis, and Mailpit for mail. Change a link under Connections > Links on the app service.

To use a managed database instead of the PostgreSQL container, see Managed databases.

Build and start

  • Gunicorn serves the application on port 8080. Do not add a flask run command or an app.run() call for deployment.
  • GUNICORN_APP is app:app: the object app in the module or package app at the root of the repository. Set the variable on the app service if your application lives elsewhere, for example to call an application factory.
  • Flask and Gunicorn are not in the image. Add both to your dependencies.
  • Set the number of workers with GUNICORN_WORKERS. Other Gunicorn settings are GUNICORN_* variables on the app service. A Gunicorn configuration file in the repository is not loaded.
  • FLASK_DEBUG is true in environments of type dev only. Wodby sets no other FLASK_* variable and no secret key. If your application uses sessions, add its SECRET_KEY as a secret variable on the app service.
  • The service's Dockerfile installs requirements.txt when the file exists. A Dockerfile from your repository replaces it and must install the dependencies itself. See Application builds.
  • Files written inside the container are lost when it is replaced.

Connect the database, Valkey, and mail

Flask does not read these variables on its own: your application code must read them. A variable is present only while its link exists and the linked service is enabled. The mail link carries no credentials.

Link Variables
Database DB_HOST, DB_PORT, DB_NAME (also DB_DATABASE), DB_USERNAME, DB_PASSWORD, DB_DRIVER (also DB_CONNECTION)
Valkey REDIS_HOST, REDIS_PORT, REDIS_PASSWORD
Mail SMTP_HOST, SMTP_PORT

Valkey writes nothing to disk unless you add a data volume, and it can evict any key at its memory limit. For a job queue or sessions, set VALKEY_MAXMEMORY_POLICY to noeviction on the Valkey service and size VALKEY_MAXMEMORY to fit.

Gotenberg has no link. Its address is http://gotenberg:3000; put it in your own configuration. See the Gotenberg guide.

Mail

Mailpit captures every message and delivers none, so use it for development and testing. Its public domains are protected by basic auth by default. Find the password under Endpoints > Auths, see Endpoints. Mailpit accepts SMTP without authentication or TLS, so configure the application's mail transport without them.

For real delivery, enable OpenSMTPD, point the app service's mail link to it, and attach an SMTP provider. See the OpenSMTPD guide.

Data and backups

PostgreSQL stores data on a data volume of 20 GB. Its backups are gzipped SQL dumps of the environment's database. An import replaces the contents of the data volume. See Application backups and Application imports.

Development workspace

In a development workspace:

  • Gunicorn reloads when you save a Python file.
  • Run workspace preparation again after changing dependencies.