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

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when a Cloud Function triggered by Pub/Sub fails?

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

What is the behavior of the system when the function fails to process a message?

A The message is immediately deleted from the Pub/Sub subscription and lost.

B The message is retried automatically until the function succeeds or the message expires.

C The message is sent to a dead-letter topic immediately after the first failure.

D The function stops processing any further messages until the error is fixed.

💡 Hint

Think about how Pub/Sub handles message delivery guarantees.

Pub/Sub retries delivering messages to the Cloud Function until the message is acknowledged or expires. This ensures at-least-once delivery.

❓ Configuration

intermediate

Which IAM role is required for a Cloud Function to subscribe to a Pub/Sub topic?

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

Which IAM role must be granted to the Cloud Function's service account to allow it to receive messages?

A roles/pubsub.publisher

B roles/pubsub.subscriber

C roles/cloudfunctions.invoker

D roles/pubsub.viewer

💡 Hint

Consider the permissions needed to pull messages from a subscription.

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

❓ Architecture

advanced

Designing a scalable Cloud Function triggered by Pub/Sub for high message volume

You expect a very high volume of messages published to a Pub/Sub topic. You want your Cloud Function to process these messages efficiently without losing any.

Which design approach best supports scalability and reliability?

A Use a single Cloud Function triggered by the Pub/Sub topic with default settings.

B Configure the Cloud Function with a higher max instances limit and enable concurrency if supported.

C Deploy multiple Cloud Functions each subscribed to the same topic to share the load manually.

D Use a pull subscription and manually poll messages inside the Cloud Function.

💡 Hint

Think about how Cloud Functions scale automatically and how concurrency affects throughput.

Increasing max instances and enabling concurrency allows the Cloud Function to handle more messages in parallel, improving scalability and reliability.

❓ security

advanced

Securing Cloud Functions triggered by Pub/Sub to prevent unauthorized invocation

You want to ensure that only Pub/Sub can trigger your Cloud Function and no other service or user can invoke it directly.

Which configuration enforces this security requirement?

A Set the Cloud Function to allow unauthenticated invocations.

B Grant the Cloud Function's invoker role to the Pub/Sub service account only.

C Disable authentication on the Cloud Function endpoint.

D Use a firewall rule to block all incoming traffic except from Pub/Sub IPs.

💡 Hint

Consider how Cloud Functions control who can invoke them.

Granting the invoker role only to the Pub/Sub service account restricts invocation to Pub/Sub messages, preventing unauthorized access.

✅ Best Practice

expert

Handling message duplication in Cloud Functions triggered by Pub/Sub

Pub/Sub guarantees at-least-once delivery, which means your Cloud Function might receive the same message multiple times.

What is the best practice to handle potential duplicate message processing in your Cloud Function?

A Ignore duplicates because Pub/Sub ensures messages are unique.

B Implement idempotent processing by tracking message IDs and ignoring repeats.

C Delete messages manually from Pub/Sub after processing to avoid duplicates.

D Use a global lock in the Cloud Function to prevent concurrent executions.

💡 Hint

Think about how to safely handle repeated messages without side effects.

Idempotent processing ensures that processing the same message multiple times does not cause unintended effects. Tracking message IDs helps detect duplicates.