Dead letter topics in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Purpose of Dead Letter Topics in Pub/Sub

What is the main purpose of a dead letter topic in Google Cloud Pub/Sub?

A To store messages that failed to be delivered after multiple attempts for later analysis or reprocessing.

B To route all incoming messages to multiple subscribers simultaneously.

C To automatically delete messages that are successfully processed to save storage space.

D To encrypt messages before they are published to the main topic.

💡 Hint

Think about what happens to messages that cannot be processed properly.

Dead letter topics hold messages that could not be delivered or processed after retries, allowing developers to inspect and handle them separately.

❓ Configuration

intermediate

Configuring Dead Letter Topic in Pub/Sub Subscription

Which configuration snippet correctly sets a dead letter topic for a Pub/Sub subscription using gcloud CLI?

A gcloud pubsub subscriptions create my-sub --topic=my-topic --dead-letter-topic=my-dead-letter-topic --max-delivery-attempts=5

B gcloud pubsub subscriptions create my-sub --topic=my-topic --dead-letter-topic=my-topic --max-delivery-attempts=5

C gcloud pubsub subscriptions create my-sub --topic=my-topic --dead-letter-topic=my-dead-letter-topic

D gcloud pubsub subscriptions create my-sub --topic=my-topic --max-delivery-attempts=5

💡 Hint

Remember to specify both the dead letter topic and max delivery attempts.

Option A correctly sets the dead letter topic and the maximum delivery attempts, which are required for dead letter handling.

❓ Architecture

advanced

Designing a Reliable Message Processing System with Dead Letter Topics

You want to design a Pub/Sub system that processes messages reliably and handles failures gracefully. Which architecture best uses dead letter topics?

A Use multiple subscriptions on the main topic without dead letter topics, relying on automatic retries only.

B Use a main topic with a subscription that has a dead letter topic configured. Failed messages go to the dead letter topic for separate processing and alerting.

C Send all messages directly to a dead letter topic and process them immediately.

D Use a single subscription without dead letter topics and discard messages after one failed attempt.

💡 Hint

Consider how to separate failed messages for special handling.

Option B uses dead letter topics to isolate failed messages, allowing for retries and separate failure handling, improving reliability.

❓ security

advanced

Permissions Required for Dead Letter Topics

Which IAM role must a Pub/Sub subscription have on the dead letter topic to successfully publish failed messages?

A roles/pubsub.editor

B roles/pubsub.subscriber

C roles/pubsub.publisher

D roles/pubsub.viewer

💡 Hint

Think about what action the subscription performs on the dead letter topic.

The Pub/Sub service account must have the roles/pubsub.publisher role on the dead letter topic to publish failed messages there.

❓ service_behavior

expert

Behavior of Message Delivery with Dead Letter Topics

Consider a Pub/Sub subscription with a dead letter topic configured and max delivery attempts set to 3. What happens when a message fails processing 3 times?

A The message is sent to the dead letter topic only after the 4th failed attempt.

B The message is retried indefinitely until acknowledged, ignoring the max delivery attempts.

C The message is deleted silently after the 3rd failed attempt without being sent to the dead letter topic.

D The message is sent to the dead letter topic after the 3rd failed attempt and is not redelivered to the subscription.

💡 Hint

Recall how max delivery attempts relate to dead letter topic delivery.

After the configured max delivery attempts (3), the message is moved to the dead letter topic and no longer retried on the original subscription.