Flask project

• Every backend project is also a python project. Make sure you read everything about python project (TODO: link) since everything applies also for backend projects.

• Backend projects has a create_app method in src/<project>/__init__.py module. create_app method accepts one argument config, which is later passed to backend_common.create_app. create_app method returns an flask application object which is created using backend_common.create_app helper method, eg:

  import backend_common
  
  def create_app(config=None):
      bac
  

• Deployment will look for an app object in <project>.flask module and for this reason you need to create flask.py module, which uses create_app from previous section, eg:

  import <project>
  
  app = <project>.create_app()
  

• Flask applications are configured using settings.py file.

  src/<project>/settings.py - configuration for Flask application

• <service>/__init__.py - this is where app (aka Flask app) should be present

• <service>/api.py|api.yml - connexion stuff (needs api extra)

• testing backend applications

Extensions

Backend extensions are simple glue code of a recognized flask pattern (TODO: link) that describes how to extend flask application.

The purpose of extensions is to

Extentions are always loaded in order which is defined in EXTENTIONS variable in lib/backend_common/backend_common/__init__.py.

Current extensions are:

• api: Provides a well defined way how to create JSON API backend servies by integrating connexion python package.

  app.api.register is a helper method to let you register Swagger/OpenAPI specifications. eg:

  def create_app(config=None):
      app = backend_common.create_app(...)
      app.api.register(os.path.join(os.path.dirname(__file__), 'api.yml'))
      return app
  

• auth

• auth0

• cache

• cors

• db

• log

• pulse

• security

• templates

Create new extension

• Create a python in lib/backend_common/backend_common/<extension_name>.py

• If extra dependencies are needed create an extra with extension name in lib/backend_common/setup.py. Look for EXTRAS variable.

• Extention needs to implement init_app method which accepts one argument app (flask application object). The init_app method must return an extension object, which can be then accessed in any backend application via app.<extension_name>.

  Example for cache extension:

  import flask_cache
  
  cache = flask_cache.Cache()
  
  def init_app(app):
      # read cache configuration from flask configuration and provide sane
      # defaults
      cache_config = app.config.get(
          'CACHE',
          {'CACHE_TYPE': 'simple'},
      )
      cache.init_app(app, config=cache_config)
      return cache
  

• Add the extension name of the file (without the .py) extension to the EXTENTIONS list in lib/backend_common/backend_common/__init__.py