Pub/Sub with Cloud Functions integration in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when a Cloud Function subscribed to a Pub/Sub topic throws an error?

You have a Cloud Function triggered by a Pub/Sub topic. The function processes messages but sometimes throws an error during execution.

What is the behavior of Pub/Sub and the Cloud Function when an error occurs?

A The message is acknowledged and removed from the subscription, so it is not retried.

B The message is not acknowledged and is retried until the function succeeds or the message expires.

C The message is sent to a dead-letter topic immediately without retries.

D The Cloud Function automatically scales down to zero and stops receiving messages.

💡 Hint

Think about how Pub/Sub handles message acknowledgment and retries.

When a Cloud Function triggered by Pub/Sub throws an error, the message is not acknowledged. Pub/Sub retries delivering the message until the function succeeds or the message expires based on the subscription's ack deadline and retention policy.

❓ Configuration

intermediate

Which IAM role must be granted to a Cloud Function to allow it to be triggered by a Pub/Sub topic?

You want to deploy a Cloud Function that triggers when messages are published to a specific Pub/Sub topic.

Which IAM role should you assign to the Cloud Function's service account to allow this trigger?

A roles/pubsub.publisher

B roles/pubsub.subscriber

C roles/cloudfunctions.invoker

D roles/pubsub.viewer

💡 Hint

Consider which role allows receiving messages from Pub/Sub.

The Cloud Function needs the 'roles/pubsub.subscriber' role to pull messages from the Pub/Sub subscription and be triggered properly.

❓ Architecture

advanced

How to design a reliable system to process Pub/Sub messages with Cloud Functions ensuring no message loss?

You need to build a system where Cloud Functions process Pub/Sub messages reliably without losing any messages, even if the function fails temporarily.

Which design choice best ensures message durability and processing reliability?

A Use a Pub/Sub topic with a subscription that has a dead-letter topic configured and Cloud Functions with retry enabled.

B Use a Pub/Sub topic with no dead-letter topic and disable retries on Cloud Functions to avoid duplicate processing.

C Use Cloud Storage to store messages and trigger Cloud Functions on file creation instead of Pub/Sub.

D Use a Pub/Sub topic with a push subscription directly calling the Cloud Function URL without retries.

💡 Hint

Think about how to handle failed messages and retries safely.

Configuring a dead-letter topic allows failed messages to be captured for later inspection. Enabling retries on Cloud Functions ensures messages are retried until successful processing, preventing message loss.

❓ security

advanced

Which practice improves security when integrating Pub/Sub with Cloud Functions?

You want to secure your Cloud Function triggered by Pub/Sub so that only authorized messages can invoke it.

Which practice best enhances security in this integration?

A Use a push subscription with an authentication token and verify it in the Cloud Function code.

B Use a pull subscription and grant the Cloud Function's service account the subscriber role only.

C Make the Cloud Function public and rely on Pub/Sub topic permissions to restrict access.

D Disable authentication on the Cloud Function to allow all Pub/Sub messages to trigger it.

💡 Hint

Consider how to authenticate messages sent to the Cloud Function.

Using a push subscription with an authentication token ensures that only Pub/Sub can invoke the Cloud Function. Verifying the token in the function code adds an extra security layer.

✅ Best Practice

expert

What is the best way to handle high-throughput Pub/Sub message processing with Cloud Functions to avoid cold starts and throttling?

Your system receives a high volume of Pub/Sub messages. You use Cloud Functions to process them, but you notice cold starts and throttling affecting performance.

Which approach best addresses these issues?

A Use Cloud Run with Pub/Sub push subscription for better scaling and control over concurrency.

B Increase the memory allocation of Cloud Functions to reduce cold start time.

C Use multiple Cloud Functions with different Pub/Sub topics to distribute load evenly.

D Disable retries on Cloud Functions to reduce duplicate invocations and throttling.

💡 Hint

Think about alternatives to Cloud Functions that handle scaling better.

Cloud Run provides better control over concurrency and scales smoothly for high-throughput workloads, reducing cold starts and throttling compared to Cloud Functions.