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Archetype for OpenAPI microservices based on Flask and Connexion

Project description

FOCA_logoDevelop Flask microservices quickly!

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FOCA (Flask-OpenAPI-Connexion-Archetype) is an opinionated archetype that enables fast development of OpenAPI-based HTTP API microservices in Flask, leveraging the excellent Connexion framework.

FOCA reduces the required boilerplate code to fire up your app to a bare minimum and allows you to focus on your application logic. It also avoids unnecessary code repetition and introduces cross-service consistency when developing multiple applications. Simply write a configuration file, pass it to FOCA and you're good to go!

Currently supported features:

  • Manage app configuration
  • Handle exceptions
  • Register OpenAPI 2.x/3.x specifications
  • Protect endpoints via JWT validation
  • Register MongoDB collections
  • Run asynchronous tasks via RabbitMQ & Celery
  • CORS support

Check the API docs for further details.

Table of Contents


(1) Install the FOCA package with pip:

pip install foca

(2) Create a configuration file.

(3) Import the FOCA class and pass your config file:

from foca import Foca

foca = Foca(config_file="path/to/my/app/config.yaml")
app = foca.create_app()  # returns a Connexion app instance

(4) Start your Flask app as usual.

Hint Check out the Petstore example application shipped with this repository to see FOCA in action!


Hint In order to get you started writing your own app configuration, you can copy the annotated template shipped with this repository and modify it.

In order to use FOCA functionalities, you must create a YAML configuration file that includes keyword sections reserved by FOCA. The following top-level sections are interpreted by FOCA (exhaustive; links are provided to the corresponding sections in this documentation, as well as to the corresponding models in the API docuementation):

Any values passed to reserved keywords are automatically validated, and a corresponding informative exception will be raised whenever a value does not adhere to the corresponding model as described in the API documentation. If you do not want to make use of a specific FOCA functionality, simply omit the corresponding section.

Configuring OpenAPI specifications

The api section is used to specify any OpenAPI specifications consumed as part of your application. Essentially, FOCA adds a wrapper around Connexion, which validates requests/responses and can serve the specifications as well as a Swagger-based user interface to explore the API. FOCA supports multiple specification files (versions Swagger/OpenAPI 2.x, OpenAPI 3.x and mixed) and multiple fragments thereof, and it adds additional features that allow easy modification of specifications on the fly. In particular, links to routers and security definitions can be added to each specified endpoint.


    - path:
        - path/to/openapi/specs.yaml
        - path/to/openapi/additions.yaml
        x-openapi-router-controller: myapi.controllers
        x-bearerInfoFunc: app.validate_token
      disable_auth: False
        strict_validation: True
        validate_responses: True
          swagger_ui: True
          serve_spec: True
    - path:
        - path/to/openapi/other_specs.yaml

In this example, the configuration file lists two separate specifications. The first is a composite one that FOCA will compile from two files, path/to/openapi/specs.yaml and path/to/openapi/additions.yaml. It comes with a range of different explicitly specified parameters to further customize the specification itself (classes/functions implementing controllers and token validation are linked to each endpoint via add_operation_fields; x-openapi-router-controller and x-bearerInfoFunc can be used to link controller functions/classes and authorization validation functions to endpoints, respectively. Furthermore, a flag to disable the need for passing authorization tokens and several Connexion options are explicitly set for this specification. In contrast, only the path to a single file is specified for the second specification, implying default values for all other options.

Further support for validating authorization can also be added to specifications via the add_security_fields parameter under specs (not shown here). Cf. the API model for this and other options, as well as further details.

Configuring MongoDB

FOCA can register one or more MongoDB databases and/or collections for you. To use that functionality, simply include the top-level db keyword section in your configuration file and tune its behavior through the available parameters.


  host: mongodb
  port: 27017
            - keys:
                id: 1
                'unique': True
            - keys:
                other_id: 1
            - keys:
                third_id: 1

In this example, two databases (myDb and myOtherDb) are configured, the former with two and the latter with one collection (myCollection, mySecondCollection and myThirdCollection, respectively). FOCA will automatically register and initialize these databases and collections for you and add convenient clients to the app instance (accessible as children of current_app.config.foca in an application context). The collections would be indexed by keys id, other_id and third_id, respectively. Out of these, only id will be required to be unique.

Cf. the API model for further options and details.

Configuring exceptions

FOCA provides a convenient, configurable exception handler and a simple way of adding new exceptions to be used with that handler. To use it, specify a top-level exceptions section in the app configuration file.


  required_members: [['msg'], ['status']]
  status_member: ['status']
  exceptions: my_app.exceptions.exceptions
  logging: one_line

This example configuration would attach the exceptions defined in the my_app.exceptions.exceptions dictionary to the exception handler. The exception handler ensures that every exception in that dictionary defines at least members msg and status. Out of these, status will be used to inform the status code for the error response. Exceptions processed via FOCA's exception handler will be automatically logged, if requested. In this case, the handler is configured to log all errors verbosely (including any traceback information, if applicable) on a single line (other rendering options are also supported).

You may further configure optional members, a list of public members (to be included in error responses) and private members (only visible in logs). Cf. the API model for further options and details.

Configuring asynchronous tasks

FOCA offers limited support for running asynchronous tasks via the RabbitMQ broker and Celery. To make use of it, include the jobs top-level section in the app configuration file.


  host: rabbitmq
  port: 5672
  backend: 'rpc://'
    - my_app.tasks.my_task_1
    - my_app.tasks.my_task_2

This config attaches the rabbitmq broker host running on port 5672 to FOCA and registers the tasks found in modules my_task_1 and my_task_2.

Cf. the API model for further details.

The foca.Foca class provides a method .create_celery_app() that you can use in your Celery worker entry point to crate a Celery app, like so:

from foca import Foca

foca = Foca(config="my_app/config.yaml")
my_celery_app = foca.create_celery_app()

Configuring logging

FOCA allows you to specify a YAML-based logging configuration to control your application's logging behavior in an effort to provide a single configuration file for every application. To use it, simply add a log top-level section in your app configuration file.


  version: 1
  disable_existing_loggers: False
      class: logging.Formatter
      style: "{"
      format: "[{asctime}: {levelname:<8}] {message} [{name}]"
      class: logging.StreamHandler
      level: 20
      formatter: standard
      stream: ext://sys.stderr
    level: 10
    handlers: [console]

The logging configuration is simply passed on to Python's `logging' package, and so it has to conform with that [package's requirements][res-python-logging]. See [here][res-python-logging-how-to] for more info.

Configuring security

FOCA offers some convenience functionalities for securing your app. Specifically, it allows you to configure the validation of JSON Web Token (JWT)-based authorization, a Casbin-based access control model, and the use of cross-origin resource sharing (CORS). To make use of them, include the security top-level section in your app configuration, as well as the desired sublevel section(s):

      - RS256
    allow_expired: False
      - userinfo
      - public_key
    validation_checks: any
    api_specs: 'path/to/your/access/control/specs'
    api_controllers: 'path/to/your/access/control/spec/controllers'
    api_route: '/route/to/access_control_api'
    db_name: access_control_db_name
    collection_name: access_control_collection_name
    model: access_control_model_definition
    enabled: True

In this example, the validation of JWT Bearer tokens would make use of the RS256 algorithm, would not allow expired tokens and would grant access to a protected endpoint if any of the two listed validation methods (via the identity provider's /userinfo endpoint or its JSON Web Key (JWK) public key. Furthermore, the application created with this config would provide an access control model model. Corresponding permissions could be accessed and altered by a user with admin permissions via the dedicated endpoints defined in the api_specs, operationalized by the controllers in api_controllers and hosted at api_route. Permissions will be stored in collection collection_name of a dedicated MongoDB database db_name. Finally, CORS would be enabled for this application.

Cf. the API model for further options and details.

Note: A detailed explaination of the access control implementation can be found here.

Configuring the server

FOCA allows you to pass certain basic configuration options to your Flask application. To modify defaults, include the top-level server keyword section in your app configuration file:

  host: ''
  port: 8080
  debug: True
  environment: development
  use_reloader: False

This config would create an application server hosting a Flask development environment at, Flask's debugger switched on, and its reloader off.

Cf. the API model for further options and details.

Custom configuration

If you would like FOCA to validate your custom app configuration (e.g., parameters required for individual controllers, you can provide a path, in dot notation, to a pydantic BaseModel-derived model. FOCA then tries to instantiate the model class with any custom parameters listed under keyword section custom.

Suppose you have a model like the following defined in module my_app.custom_config:

from pydantic import BaseModel

class CustomConfig(BaseModel):
    my_param: int = 5

And you have, in your app configuration file my_app/config.yaml, the following section:

  my_param: 10

You can then have FOCA validate your custom configuration against the CustomConfig class by including it in the Foca() call like so:

from foca import Foca

foca = Foca(
my_app = foca.create_app()

We recommend that, when defining your pydantic model, that you supply default values wherever possible. In this way, the custom configuration parameters will always be available, even if not explicitly listed in the app configuration (like with the FOCA-specific parameters).

Note that there is tooling available to automatically generate pydantic models from different file formats like JSON Schema etc. See here for the [datamodel-code-generator][res-datamodel-code-generator] project.

Apart from the reserved keyword sections listed above, you are free to include any other sections and parameters in your app configuration file. FOCA will simply attach these to your application instance as described above and shown below. Note, however, that any such parameters need to be manually validated. The same is true if you include a custom section but do not provide a validation model class via the custom_config_model parameter when instantiating Foca.


my_custom_param: 'some_value'

  another_custom_param: 3
    - 1
    - 2
    - 3

Accessing configuration parameters

Once the application is created using foca(), one can easily access any configuration parameters from within the application context through `current_app.config.foca like so:

from flask import current_app

app_config = current_app.config.foca

db = app_config.db
api = app_config.api
server = app_config.server
exceptions = app_config.exceptions
security =
jobs =
log = app_config.log
app_specific_param = current_app.config['app_specific_param']

Outside of the application context, configuration parameters are available via app.config.foca in a similar way.

More examples

Apart from the annotated template, you can also check out the configuration file of the Petstore app for another example.

Hint Or why not explore apps that already use FOCA?


FOCA provides some functions that may be useful for several applications. Simply import them if you want to use them.

Database utilities

FOCA provides the following general-purpose MongoDB controllers:

  • Fetch latest object given the db collection:
from foca.utils.db import find_one_latest

latest_object = find_one_latest("your_db_collection_instance")
  • Fetch latest object identifier (id) given the db collection:
from foca.utils.db import find_id_latest

latest_object_id = find_id_latest("your_db_collection_instance")

Logging utilities

FOCA provides a decorator that can be used on any route to automatically log any requests and/or responses passing through that route:

from foca.utils.logging import log_traffic

@log_traffic(log_request=True, log_response=True, log_level=20)
def your_controller():

The above decorater will log both requests and responses with the specified logging level (20, or INFO).

Miscellaneous utilities

  • Generate a random object from a given character set:
import string

from foca.utils.misc import generate_id

obj_id = generate_id(charset=string.digits, length=6)

The above function processes and returns a random obj_id of length 6 consisting of only digits (string.digits).

Access Control utilities

FOCA provides a decorator that can be used on any route to automatically validate request on the basis of permission rules.

from import (

def your_controller():


This project is a community effort and lives off your contributions, be it in the form of bug reports, feature requests, discussions, or fixes and other code changes. Please refer to our organization's contributing guidelines if you are interested to contribute. Please mind the code of conduct for all interactions with the community.


The project adopts semantic versioning. Currently the service is in beta stage, so the API may change without further notice.


This project is covered by the Apache License 2.0 also shipped with this repository.


The project is a collaborative effort under the umbrella of ELIXIR Cloud & AAI. Follow the link to get in touch with us via chat or email. Please mention the name of this service for any inquiry, proposal, question etc.


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