Emulating your Python Google Cloud function locally (Python 3)

README.md

Emulating your own Python Google Cloud Function (Python >=3.6)

Python Google Cloud Functions have been introduced publically in Q3-Q4 2018. Deploying them takes time (2-10 minutes with gcloud functions deploy. Actually, a Python cloud function equates to a Flask handler. Thus, you can test them cloud function first on your own computer. This spares you from long deployments, difficult step-by-step debugging and bad GCP weather.

Here is how:

1. keep the traditional Python Cloud Function requirements.txt and main.py untouched.
2. add emulator-requirements.txt (a super-set combining a flask module + the requirements.txt's contents)
3. add emulator.py
4. leave any Python virtual environment and make one out of emulator-requirements.txt

• Example: mkvirtualenv my_function_emulator -p /usr/bin/python3.6; workon my_function emulator
• then: pip install -r emulator-requirements.txt

1. run python emulator.py within that new virtual environment
2. keep the Flask server running, then test it by running sh local_curl_tests.sh
3. kill your Flask server (Ctrl+C in the emulator.py window)
4. deploy your Cloud Function using sh deploy.sh
5. test it using sh remote_curl_tests.sh
6. You are a super star!! Tap yourself on the shoulder : )

deploy.sh

#!/bin/sh
gcloud beta functions deploy my_function --runtime python37 --trigger-http --region=europe-west1 --memory=128MB

emulator-requirements.txt

Flask==1.0.2

emulator.py

#!/usr/bin/env python3
"""
Cloud function emulator for running main.py locally.
"""
# Per
# https://github.com/GoogleCloudPlatform/cloud-functions-emulator/issues/268#issuecomment-422919983
from flask import Flask, request

from main import my_function


APP = Flask(__name__)


def wrapper():
    """ Runs the main app, without having it depend
    on flask too much (Cloud Function)."""
    return my_function(request)


wrapper.provide_automatic_options = False  # type: ignore
wrapper.methods = ['GET', 'POST', 'PUT', 'DELETE']  # type: ignore
APP.add_url_rule('/', 'index', wrapper)

if __name__ == '__main__':
    APP.run(debug=True, port=5000)

local_curl_tests.sh

#!/bin/sh

echo "Testing cloud function LOCALLY EMULATED"
MY_FUNCTION_URL=http://localhost:5000
set -x
curl -s $MY_FUNCTION_URL -X POST -H "Content-Type: application/json" -d '{"breakfast_mode": "in_bed"}'
set +x

main.py

import os

from flask import Request, Response

def my_function(request: Request) -> Response:
    """Responds to any HTTP request.
    Args:
        request (flask.Request): HTTP request object.
    Returns:
        The response text or any set of values that can be turned into a
        Response object using
        `make_response <http://flask.pocoo.org/docs/0.12/api/#flask.Flask.make_response>`. # noqa: E501
    """
    req = request.json

    return Response(f"Your said that breakfast is: {req['breakfast_mode']", 200)

remote_curl_tests.sh

#!/bin/sh

echo "Testing cloud function DEPLOYED REMOTELY"
MY_FUNCTION_URL=`gcloud beta functions describe my_function --region=europe-west1 --format=config | grep url | awk '{ print $3 }'`
set -x
curl -s $MY_FUNCTION_URL -X POST -H "Content-Type: application/json" -d '{"breakfast_mode": "in_bed"}'
set +x

requirements.txt

# Nothing
# Google cloud function provides Flask