Google Cloud Functions (GCF) runs Python code in response to HTTP requests and Google Cloud events. It integrates tightly with Firebase, Pub/Sub, and Cloud Storage.

Your First Function 

  # main.py
import functions_framework

@functions_framework.http
def hello_http(request):
    name = request.args.get('name', 'World')
    return f'Hello, {name}!'

Deploy 

  pip install functions-framework

# Local testing
functions-framework --target=hello_http --debug

# Deploy to GCP
gcloud functions deploy hello-http \
    --gen2 \
    --runtime=python312 \
    --region=us-central1 \
    --source=. \
    --entry-point=hello_http \
    --trigger-http \
    --allow-unauthenticated

JSON API Function 

  import functions_framework
import json

@functions_framework.http
def api_handler(request):
    if request.method == 'GET':
        return json.dumps([{'id': 1, 'name': 'Item'}]), 200, {'Content-Type': 'application/json'}

    if request.method == 'POST':
        data = request.get_json()
        return json.dumps({'id': 2, 'name': data['name']}), 201, {'Content-Type': 'application/json'}

    return json.dumps({'error': 'Method not allowed'}), 405

Background Event Triggers

Process Cloud Storage uploads:

  import functions_framework

@functions_framework.cloud_event
def process_upload(cloud_event):
    data = cloud_event.data
    bucket = data["bucket"]
    name = data["name"]
    print(f"Processing gs://{bucket}/{name}")
    # Download and process the file...

Deploy with a storage trigger:

  gcloud functions deploy process-upload \
    --gen2 \
    --runtime=python312 \
    --region=us-central1 \
    --source=. \
    --entry-point=process_upload \
    --trigger-event-filters="type=google.cloud.storage.object.v1.finalized" \
    --trigger-event-filters="bucket=my-bucket"

Pub/Sub Trigger 

  @functions_framework.cloud_event
def pubsub_handler(cloud_event):
    import base64
    message = base64.b64decode(cloud_event.data["message"]["data"]).decode()
    print(f"Received message: {message}")

Requirements

Create requirements.txt for dependencies:

  functions-framework==3.*
requests==2.31.0
google-cloud-storage==2.*

Cloud Functions automatically installs dependencies during deployment.

Firebase Integration

Cloud Functions integrate with Firebase for mobile/web backends:

  from firebase_functions import https_fn

@https_fn.on_request()
def hello_firebase(req: https_fn.Request) -> https_fn.Response:
    return https_fn.Response("Hello from Firebase!")

Deploy with Firebase CLI:

  firebase deploy --only functions

Best Practices

  1. Use Gen 2 functions for better performance and CloudEvent support
  2. Set memory and timeout appropriately in deployment config
  3. Use Secret Manager for sensitive configuration
  4. Enable Cloud Logging for debugging and monitoring
  5. Keep cold start times low — minimize dependencies

Google Cloud Functions excels when your stack is already on GCP or Firebase.