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Generative AI > Google Gemini API > ADK with Pub/Sub for Event-Driven Agents

ADK with Pub/Sub for Event-Driven Agents

Author: Venkata Sudhakar

Google Cloud Pub/Sub enables asynchronous messaging between services. ADK agents can subscribe to Pub/Sub topics and trigger actions when messages arrive - without polling. ShopMax India uses this pattern to trigger inventory reorder agents when stock levels drop below threshold.

The integration works by deploying an ADK agent as a Cloud Run service that exposes an HTTP endpoint. A Pub/Sub push subscription delivers messages to that endpoint. The agent processes the payload and responds.

The below example shows how ShopMax India builds a Pub/Sub triggered reorder agent that processes stock alert messages.

The Cloud Run HTTP handler that receives Pub/Sub push messages,

from flask import Flask, request, jsonify
from google.adk.runners import Runner
from google.adk.sessions import InMemorySessionService
import base64, json

app = Flask(__name__)
session_service = InMemorySessionService()

@app.route("/pubsub-handler", methods=["POST"])
def handle_pubsub():
    # Decode Pub/Sub message
    envelope = request.get_json()
    raw = base64.b64decode(envelope["message"]["data"]).decode("utf-8")
    alert = json.loads(raw)

product_id = alert["product_id"]
    current_stock = alert["current_stock"]

# Build prompt for the agent
    prompt = f"Stock alert: {product_id} has only {current_stock} units left. Place a reorder of 100 units."

runner = Runner(agent=agent, session_service=session_service, app_name="shopmax")
    session = session_service.create_session(app_name="shopmax", user_id="system")

from google.adk.types import Content, Part
    result = runner.run(session_id=session.id, user_id="system",
                        new_message=Content(parts=[Part(text=prompt)]))
    for event in result:
        if event.is_final_response():
            return jsonify({"result": event.content.parts[0].text}), 200

return jsonify({"result": "processed"}), 200

if __name__ == "__main__":
    app.run(port=8080)

It gives the following output when a Pub/Sub message arrives,

Pub/Sub message received for: LAPTOP-DELL-XPS-15
Current stock: 3 units
Agent response: Reorder placed - 100 units of LAPTOP-DELL-XPS-15
Supplier: ShopMax Wholesale Delhi
Expected delivery: 3-5 business days

To set up the Pub/Sub subscription, create a push subscription pointing to your Cloud Run endpoint. Messages published to the stock-alerts topic are automatically forwarded to your agent for processing without any polling loop.

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