Topics and subscriptions in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Message Delivery Behavior in Pub/Sub

In Google Cloud Pub/Sub, what happens if a subscriber does not acknowledge a message within the acknowledgement deadline?

A The message is redelivered to the subscriber or another subscriber.

B The message is moved to a dead-letter topic immediately.

C The message is deleted and not delivered again.

D The message is archived automatically without redelivery.

💡 Hint

Think about what happens when a message is not confirmed as received.

If a subscriber does not acknowledge a message within the acknowledgement deadline, Pub/Sub assumes the message was not processed and redelivers it to the same or another subscriber to ensure reliable delivery.

❓ Architecture

intermediate

Designing Pub/Sub for Multiple Subscribers

You want to send the same messages to multiple independent services using Pub/Sub. Which setup ensures each service receives all messages independently?

A Create one topic and multiple subscriptions, one per service.

B Create one subscription and use message filters to route messages.

C Create multiple topics, one per service, and one subscription per topic.

D Create one topic and one subscription shared by all services.

💡 Hint

Remember that each subscription receives its own copy of messages.

In Pub/Sub, each subscription receives a copy of every message published to the topic. To deliver messages independently to multiple services, create one subscription per service on the same topic.

❓ security

advanced

Restricting Publisher Access to a Pub/Sub Topic

You want to allow only a specific service account to publish messages to a Pub/Sub topic. Which IAM role and policy setup achieves this?

A Grant the 'roles/pubsub.subscriber' role to the service account on the topic resource.

B Grant the 'roles/pubsub.publisher' role to the service account on the topic resource.

C Grant the 'roles/pubsub.editor' role to the service account on the project.

D Grant the 'roles/owner' role to the service account on the subscription.

💡 Hint

Think about the role that allows publishing messages.

The 'roles/pubsub.publisher' role grants permission to publish messages to a topic. Assigning it to the service account on the topic resource restricts publishing to only that account.

❓ Configuration

advanced

Configuring Dead-Letter Topics for Pub/Sub Subscriptions

Which configuration is required to enable a dead-letter topic for a Pub/Sub subscription?

A Create a subscription on the dead-letter topic and link it to the original topic.

B Enable message retention on the topic and set a dead-letter policy on the subscription.

C Set the dead-letter topic in the subscription and specify the maximum delivery attempts.

D Assign the 'roles/pubsub.deadletterHandler' role to the subscription.

💡 Hint

Dead-letter topics require a policy on the subscription with delivery attempt limits.

To enable dead-lettering, you configure the subscription with a dead-letter topic and set the maximum number of delivery attempts before messages are sent to the dead-letter topic.

✅ Best Practice

expert

Optimizing Pub/Sub Subscription Acknowledgement Deadline

You have a subscriber processing messages that sometimes takes longer than the default acknowledgement deadline. What is the best practice to avoid message redelivery without losing messages?

A Disable acknowledgement to prevent message redelivery.

B Increase the acknowledgement deadline to the maximum allowed value permanently.

C Set the acknowledgement deadline to the minimum and rely on message redelivery.

D Use the subscriber client to extend the acknowledgement deadline dynamically while processing.

💡 Hint

Think about how to handle variable processing times safely.

Extending the acknowledgement deadline dynamically during message processing prevents premature redelivery while ensuring messages are acknowledged only after successful processing.