Publishing messages in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Message Ordering in Pub/Sub

You have a Google Cloud Pub/Sub topic with message ordering enabled. What happens if you publish messages with the same ordering key but the subscriber acknowledges messages out of order?

A Messages with the same ordering key are delivered in the order they were published, regardless of acknowledgment order.

B Messages are delivered in any order, and acknowledgment order does not affect delivery.

C Messages with the same ordering key are redelivered until acknowledged in the correct order, blocking later messages.

D Messages with the same ordering key are dropped if acknowledged out of order.

💡 Hint

Think about how Pub/Sub ensures message order with ordering keys and what happens if acknowledgments are delayed or out of order.

Pub/Sub with ordering keys ensures messages are delivered in order. If a message is not acknowledged, subsequent messages with the same key are not delivered until the earlier message is acknowledged, causing redelivery attempts.

❓ Architecture

intermediate

Designing a Scalable Pub/Sub Publisher

You want to design a system that publishes millions of messages per second to a Google Cloud Pub/Sub topic. Which approach best ensures scalability and reliability?

A Use multiple publisher client instances with asynchronous publishing and batching enabled.

B Use a single publisher client instance with synchronous publishing calls to ensure message order.

C Publish messages directly from client devices without batching or retries.

D Use a single publisher client instance with manual retries and no batching.

💡 Hint

Consider how batching and asynchronous publishing affect throughput and reliability.

Multiple publisher clients with asynchronous publishing and batching improve throughput and reliability by sending messages in batches and retrying failures automatically.

❓ security

advanced

Securing Pub/Sub Message Publishing

You want to restrict who can publish messages to a Pub/Sub topic in your project. Which IAM role should you assign to the publisher service account to allow publishing but prevent subscription management?

A roles/pubsub.editor

B roles/pubsub.admin

C roles/pubsub.subscriber

D roles/pubsub.publisher

💡 Hint

Think about the principle of least privilege and which role allows only publishing.

The roles/pubsub.publisher role allows publishing messages to topics but does not grant permissions to manage subscriptions or topics.

✅ Best Practice

advanced

Handling Message Duplication in Pub/Sub

Google Cloud Pub/Sub may deliver messages more than once. What is the best practice to handle this duplication in your subscriber application?

A Implement idempotent message processing using unique message IDs.

B Ignore duplicates because Pub/Sub guarantees exactly-once delivery.

C Acknowledge messages immediately without processing to avoid duplicates.

D Use message filtering to prevent duplicates from being delivered.

💡 Hint

Consider how to safely process messages that might arrive multiple times.

Pub/Sub guarantees at-least-once delivery, so duplicates can occur. Implementing idempotent processing using unique message IDs ensures safe handling of duplicates.

🧠 Conceptual

expert

Pub/Sub Message Ordering with Multiple Ordering Keys

You publish messages with multiple different ordering keys to a single Pub/Sub topic. How does Pub/Sub guarantee message ordering in this scenario?

A Pub/Sub does not guarantee any ordering when multiple ordering keys are used.

B Messages are ordered only within each ordering key; messages with different keys can be delivered out of order relative to each other.

C Messages with different ordering keys are delivered in the order they were published across all keys.

D Messages with different ordering keys are merged and delivered in alphabetical order of the keys.

💡 Hint

Think about how ordering keys isolate message order guarantees.

Pub/Sub guarantees ordering only within each ordering key. Messages with different keys can be delivered in any order relative to each other.