ucam-faas 0.1.2

Opinionated FaaS support framework extending Google's functions-framework

UCam FaaS Library

This project contains a support library and base Docker image to be used to create Function as a Service (FaaS) applications intended to be deployed to a GCP cloud run environment.

It is highly opinionated and non-configurable by design.

Usage

Install the library via pip:

pip install ucam-faas

Install the library with testing support:

pip install ucam-faas[testing]

The library provides a decorator to create a runnable application from a single function. The function must accept a dictionary as an argument, and return either a string or a dictionary as a response:

# main.py
from ucam_faas import event_handler


@event_handler
def say_hello(event):
    return "hello!"

This can then be run as a FaaS app using:

ucam-faas --debug --target say_hello

Testing FaaS Functions

To unit test FaaS functions there are two available approaches. Firstly, the unwrapped version of the function can be directly accessed. This is recommended as the primary way to test FaaS functions and requires no additional configuration:

# test_my_event_handler.py
from main import say_hello

def test_say_hello():
    assert say_hello.__wrapped__({"event_key": "event_value"}) == "hello!"

The original function version is made available through the __wrapped__ variable.

Alternatively, if required, a support testing client can be used to instantiate a version of the web application running the function. To do this the extra "testing" must also be installed:

pip install ucam-faas[testing]

Then tests can register the provided pytest fixture and use it in tests:

# test_my_event_handler.py
pytest_plugins = ["ucam_faas.testing"]

def test_say_hello(event_app_client):
    # Provide the target function for the test webapp
    eac = event_app_client("say_hello")
    response = eac.get("/")
    assert response.status_code == 200

Note that with this approach it is not necessary to import the function under test, it is discovered and imported during the test webapp setup.

Example

An example application and example tests can be found in this repository in the example directory.

Note that the example dockerfile uses a relative file FROM - this means it must be built in the context of its parent directory:

docker build -f example/Dockerfile .

Local Development

Install poetry via:

pipx install poetry
pipx inject poetry poethepoet[poetry_plugin]

Install dependencies via:

poetry install

Build the library via:

poetry build

Run the example application via:

poetry poe example

Run the tests via:

poetry poe tox

Note that the tests are found under the example directory, there are currently no tests in the root library as the code is predominantly configuration and setup, and example testing has been deemed sufficient.

Dependencies

IMPORTANT: if you add a new dependency to the application as described below you will need to run docker compose build or add --build to the docker compose run and/or docker compose up command at least once for changes to take effect when running code inside containers. The poe tasks have already got --build appended to the command line.

To add a new dependency for the application itself:

poetry add {dependency}

To add a new development-time dependency used only when the application is running locally in development or in testing:

poetry add -G dev {dependency}

To remove a dependency which is no longer needed:

poetry remove {dependency}

CI configuration

The project is configured with Gitlab AutoDevOps via Gitlab CI using the .gitlab-ci.yml file.