Set up a 12-Factor app rock

The following how-to guide provides instructions on initializing and configuring rocks for 12-factor apps.

Initialize a 12-factor app rock

Use rockcraft init and specify the relevant profile:

rockcraft init --profile <profile>

Rockcraft automatically creates a rockcraft.yaml project file for the rock in your current directory. You will need to check the project file to verify that the rock’s name and description are correct.

DjangoExpressFastAPIFlaskGo

rockcraft init --profile django-framework

For more information, see: init

Include extra files in the OCI image

The following files are included in the image by default from the root of the project:

• app (does not apply to the go-framework)

• app.py (does not apply to the go-framework)

• migrate

• migrate.sh

• migrate.py (does not apply to the go-framework)

• static

• templates

To change this list, add the following snippet to the project file:

FlaskDjangoFastAPIGo

rockcraft.yaml

  parts:
    flask-framework/install-app:
      prime:
        - flask/app/.env
        - flask/app/app.py
        - flask/app/webapp
        - flask/app/templates
        - flask/app/static

Note the flask/app/ prefix that is required followed by the relative path to the project root.

Include additional debs in the OCI image

If your app requires debs – for example, to connect to a database – add the following snippet to the project file:

FlaskDjangoFastAPIGo

rockcraft.yaml

  parts:
    flask-framework/dependencies:
      stage-packages:
        # list required packages or slices for your flask application below.
        - libpq-dev

Override commands

The services key follows the Pebble layer specification and defines the entrypoint to your app. You can override the default service commands in rockcraft.yaml.

To override a service’s command, check the default service entrypoint generated by the extension by running rockcraft expand-extensions. Then, adapt the command to your needs and declare it in your project file. For example:

FlaskDjangoFastAPIGoExpressSpring Boot

Output of rockcraft expand-extensions

# ...

services:
  flask:
    override: replace
    command: /bin/python3 -m gunicorn -c /flask/gunicorn.conf.py app:app -k [ sync ]
    startup: enabled
    after:
      - statsd-exporter
    user: _daemon_

To limit the maximum number of pending connections in Gunicorn to 1024, add the following lines to your project file.

rockcraft.yaml

services:
  flask:
    command: /bin/python3 -m gunicorn -c /flask/gunicorn.conf.py app:app --backlog 1024 -k [ sync ]