Google Pub/Sub Push Events Reach Cloud Run Service But Python Flask Handler Not Processing Gmail Notifications

I’m building a Python application to monitor Gmail messages in real-time and analyze them for security threats. My setup includes two separate Python files - one for processing existing emails and another for handling incoming live messages.

The Problem: My live message handler isn’t showing any activity when new emails arrive, even though my historical email processor works perfectly and retrieves all recent messages. Cloud Run logs confirm POST 200 responses when test emails are sent, and local testing with curl commands works fine. However, nothing appears in my local development environment logs.

My Setup:

  • Flask webhook deployed on Google Cloud Run
  • Unauthenticated access enabled during deployment
  • Pub/Sub subscription points to my Cloud Run endpoint
  • Application containerized with Docker
  • Flask configured for host=0.0.0.0, port=8080

Here’s my simplified webhook code:

from flask import Flask, request, jsonify
import base64
import logging
import json

server = Flask(__name__)
logging.basicConfig(level=logging.DEBUG)

@server.route('/notification-handler', methods=['POST'])
def process_gmail_notification():
    try:
        # Debug incoming request details
        logging.debug(f"Request headers: {dict(request.headers)}")
        logging.debug(f"Request payload: {request.data.decode('utf-8')}")

        # Process incoming JSON data
        payload = request.get_json(silent=True)
        if not isinstance(payload, dict):
            logging.error("Received invalid JSON structure.")
            return jsonify({"error": "Invalid JSON structure received."}), 400

        # Decode the notification content
        notification_content = payload.get("message", {}).get("data")
        if notification_content:
            decoded_content = base64.urlsafe_b64decode(notification_content)
            content_string = decoded_content.decode("utf-8")
            logging.info(f"Notification content: {content_string}")
        else:
            logging.warning("Missing notification content in request.")
            return jsonify({"error": "Missing notification content."}), 400

        return jsonify({"result": "Processed", "content": content_string}), 200

    except Exception as error:
        logging.error(f"Processing error: {error}")
        return jsonify({"error": str(error)}), 500

if __name__ == '__main__':
    server.run(host='0.0.0.0', port=8080, debug=True)

What could be causing this disconnect between Cloud Run receiving the notifications and my local development environment not seeing them?

I ran into something similar when I first started working with Cloud Run and Pub/Sub. The disconnect you’re experiencing happens because your Pub/Sub subscription is configured to send notifications directly to your Cloud Run service URL, not your local development server. These are two completely isolated environments. When you deployed to Cloud Run, that endpoint became the active receiver for all Gmail notifications. Your local Flask app running on your machine won’t receive any of these push notifications because Pub/Sub doesn’t know about your local environment. The POST 200 responses you’re seeing in Cloud Run logs are actually your deployed service processing the notifications successfully. To see what’s really happening with your Gmail notifications, check the Cloud Run logs in Google Cloud Console under your service’s Logs tab. You should find your logging.info and logging.debug output there. For local development and testing, consider creating a separate Pub/Sub subscription that points to an ngrok tunnel or use the pull method instead of push notifications.

The issue you’re experiencing is a fundamental misunderstanding of how cloud deployments work. When you deploy your Flask application to Cloud Run, that becomes the active endpoint receiving Pub/Sub notifications - not your local development environment. Your local machine and Cloud Run are completely separate instances.

To debug what’s actually happening with incoming Gmail notifications, you need to examine the Cloud Run service logs through Google Cloud Console, not your local terminal. Navigate to Cloud Run > Your Service > Logs tab to see the actual processing output. The 200 responses you’re seeing indicate the requests are reaching Cloud Run successfully.

If you want to test locally during development, you’ll need to either redirect your Pub/Sub subscription to point to your local machine using a tool like ngrok, or pull the Cloud Run logs to understand what’s happening in production. Your current setup is working correctly - you’re just looking in the wrong place for the output.

wait your confusing me here - cloud run is getting the POST 200s but your local dev environment isnt seeing anything? those are completly different environments. if you deployed to cloud run then the notifications go there, not your local machine running the same code. you need to check cloud run logs not local logs to see whats happening.