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Part-46: Trigger a Cloud Function based on Pubsub Subscriptions in GCP


This content originally appeared on DEV Community and was authored by Latchu@DevOps

☁ Cloud Functions – Cloud Pub/Sub Trigger

Google Cloud Functions integrates seamlessly with Cloud Pub/Sub to execute code whenever a message is published to a topic. This allows for event-driven architectures where functions react to data streams in real time. 🚀

✅ Step-01: Introduction

We’ll create:

  1. A Cloud Pub/Sub Topic
  2. A Cloud Function triggered by Pub/Sub Events

✅ Step-02: Create Cloud Pub/Sub Topic

Navigate to Cloud Pub/Sub → CREATE TOPIC

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Enter the following details:

  • Topic ID: mytopic1
  • Leave the rest of the settings as default

Click CREATE

Review your setup:

  • Check that the Topic was created
  • Verify the Subscription is attached

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✅ Step-03: Create Cloud Function with Pub/Sub Trigger

Configuration Tab

  • Service name: cf-demo2-events-pubsub
  • Region: us-central1
  • Trigger: Cloud Pub/Sub
  • Topic: mytopic1
  • More Options → Review defaults
  • Click NEXT

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Code Tab

  • Runtime: Node.js 20
  • Use the auto-populated sample code (below)
  • Click Save and DEPLOY

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const functions = require('@google-cloud/functions-framework');

// Register a CloudEvent callback with the Functions Framework that will
// be executed when the Pub/Sub trigger topic receives a message.
functions.cloudEvent('helloPubSub', cloudEvent => {
  // The Pub/Sub message is passed as the CloudEvent's data payload.
  const base64name = cloudEvent.data.message.data;

  const name = base64name
    ? Buffer.from(base64name, 'base64').toString()
    : 'World';

  console.log(`Hello, ${name}!`);
});

✅ Step-04: Review Cloud Function Logs

  • Navigate to: Cloud Function → cf-demo2-events-pubsub → Logs
  • You’ll see execution logs once messages are published.

✅ Step-05: Publish Messages to the Topic

Go to Cloud Pub/Sub → mytopic1 → MESSAGES → PUBLISH MESSAGE

Enter:

  • Number of Messages: 10
  • Message Body: My Pub/Message

Click PUBLISH

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✅ Step-06: Review Logs Again

  • Go to Cloud Function Logs
  • You should see: 
Hello, My Pub/Message!

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logged multiple times (once for each published message)


This content originally appeared on DEV Community and was authored by Latchu@DevOps