Pub/Sub vs Cloud Tasks in GCP - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Pub/Sub Message Delivery

Which statement best describes how Google Cloud Pub/Sub handles message delivery?

A Pub/Sub guarantees exactly-once delivery of messages to subscribers.

B Pub/Sub guarantees at-least-once delivery, so messages may be delivered more than once.

C Pub/Sub delivers messages only once and drops duplicates automatically.

D Pub/Sub does not retry message delivery if a subscriber fails to acknowledge.

💡 Hint

Think about how Pub/Sub ensures messages are not lost but might be repeated.

Pub/Sub guarantees at-least-once delivery, meaning messages can be delivered multiple times if acknowledgments are not received.

❓ Architecture

intermediate

Choosing Between Pub/Sub and Cloud Tasks for Task Execution

You need to design a system that processes user requests with guaranteed execution and ordered processing. Which service is more suitable?

A Use Pub/Sub because it guarantees ordered message processing and exactly-once delivery.

B Use Cloud Tasks because it supports task scheduling, retries, and ordered execution.

C Use Pub/Sub because it supports task scheduling and delayed execution natively.

D Use Cloud Tasks because it only supports fire-and-forget messaging without retries.

💡 Hint

Consider which service supports task ordering and retries explicitly.

Cloud Tasks supports scheduling, retries, and ordered execution, making it suitable for guaranteed task processing.

❓ service_behavior

advanced

Pub/Sub Subscription Acknowledgment Behavior

What happens if a Pub/Sub subscriber does not acknowledge a message within the ack deadline?

A The message is deleted and never redelivered.

B The message is redelivered to the same or another subscriber after the ack deadline expires.

C The message is moved to a dead-letter queue immediately.

D The subscriber is disconnected and must reconnect manually.

💡 Hint

Think about how Pub/Sub ensures message processing reliability.

If a message is not acknowledged in time, Pub/Sub redelivers it to ensure processing.

❓ security

advanced

Securing Cloud Tasks Execution

Which method is recommended to securely authenticate HTTP targets when Cloud Tasks dispatches tasks?

A Use API keys embedded in the task payload.

B Use OAuth 2.0 tokens or OIDC tokens generated by Cloud Tasks for authentication.

C Use basic authentication with username and password in the URL.

D No authentication is needed because Cloud Tasks runs inside Google Cloud.

💡 Hint

Consider secure token-based authentication methods supported by Cloud Tasks.

Cloud Tasks supports OAuth 2.0 and OIDC tokens to authenticate HTTP targets securely.

✅ Best Practice

expert

Handling High Throughput with Pub/Sub and Cloud Tasks

You have a system that must handle millions of user events per day with low latency and guaranteed processing. Which architecture best balances scalability and reliability?

A Use Pub/Sub to ingest events and Cloud Tasks to process critical tasks with retries and ordering.

B Use only Cloud Tasks for all events to ensure ordering and retries at scale.

C Use Pub/Sub with no retries and process events directly without task queues.

D Use Cloud Tasks to ingest events and Pub/Sub to process tasks asynchronously.

💡 Hint

Think about combining services to leverage their strengths for scale and reliability.

Pub/Sub handles high throughput event ingestion well, while Cloud Tasks manages critical task processing with retries and ordering.

Practice

1. Which Google Cloud service is best suited for sending messages to multiple subscribers quickly and asynchronously?

easy

A. Cloud Functions

B. Cloud Tasks

C. Pub/Sub

D. Cloud Run

Solution

1. Step 1: Understand Pub/Sub's purpose

   Pub/Sub is designed to send messages to many subscribers quickly and asynchronously, enabling event-driven architectures.

2. Step 2: Compare with Cloud Tasks

   Cloud Tasks manages individual work items with control over retries and timing, not broad message delivery.

3. Final Answer:

   Pub/Sub -> Option C

4. Quick Check:

   Event broadcasting = Pub/Sub [OK]

Hint: Pub/Sub = many subscribers fast; Cloud Tasks = controlled retries [OK]

Common Mistakes:

• Confusing Cloud Tasks as a message broadcaster
• Thinking Pub/Sub controls task retries
• Mixing Cloud Functions with messaging services

2. Which of the following is the correct way to create a Cloud Task with a scheduled delay in Google Cloud?

easy

A. Use Pub/Sub with a delay attribute

B. Use Cloud Tasks client and set scheduleTime to future timestamp

C. Send a message to Pub/Sub and rely on subscriber delay

D. Create a Cloud Function with a timer trigger instead

Solution

1. Step 1: Identify scheduling method in Cloud Tasks

   Cloud Tasks allows setting a scheduleTime property to delay task execution until a future timestamp.

2. Step 2: Eliminate incorrect options

   Pub/Sub does not support scheduling messages; Cloud Functions timer triggers are separate services.

3. Final Answer:

   Use Cloud Tasks client and set scheduleTime to future timestamp -> Option B

4. Quick Check:

   Scheduled tasks = Cloud Tasks scheduleTime [OK]

Hint: Schedule tasks with Cloud Tasks scheduleTime, not Pub/Sub [OK]

Common Mistakes:

• Trying to delay Pub/Sub messages directly
• Confusing Cloud Functions timers with Cloud Tasks scheduling
• Assuming subscribers can delay message processing

3. Given the following scenario: A Cloud Task is created with maxAttempts set to 3 and a retry delay of 10 seconds. If the task fails twice, what happens next?

medium

A. The task is retried after 10 seconds delay for the third attempt

B. The task is retried immediately without delay

C. The task is discarded after the second failure

D. Pub/Sub resends the message automatically

Solution

1. Step 1: Understand Cloud Tasks retry policy

   Cloud Tasks retries failed tasks up to maxAttempts, applying the configured retry delay between attempts.

2. Step 2: Apply to given scenario

   After two failures, the third attempt will be retried after the 10 seconds delay before final failure or success.

3. Final Answer:

   The task is retried after 10 seconds delay for the third attempt -> Option A

4. Quick Check:

   Retries respect delay and maxAttempts in Cloud Tasks [OK]

Hint: Cloud Tasks retries wait delay before next try, up to maxAttempts [OK]

Common Mistakes:

• Assuming immediate retry without delay
• Thinking task is discarded too early
• Confusing Pub/Sub automatic retries with Cloud Tasks

4. You have a Cloud Task that never executes and keeps retrying indefinitely. What is the most likely cause?

medium

A. The Cloud Task queue is paused

B. Pub/Sub subscription is missing

C. The task's maxAttempts is set to 0 or unlimited

D. The task's scheduleTime is in the past

Solution

1. Step 1: Analyze retry behavior

   If a task retries indefinitely, it means it keeps failing but is still being retried.

2. Step 2: Check queue state

   If the Cloud Task queue is paused, tasks will not execute but may keep retrying or remain pending.

3. Step 3: Eliminate other options

   Pub/Sub subscription missing is unrelated to Cloud Tasks; maxAttempts 0 means no retries; scheduleTime in past triggers immediate execution.

4. Final Answer:

   The Cloud Task queue is paused -> Option A

5. Quick Check:

   Paused queue blocks task execution causing retries [OK]

Hint: Paused queue stops tasks but retries may appear stuck [OK]

Common Mistakes:

• Confusing Pub/Sub with Cloud Tasks
• Assuming maxAttempts 0 means infinite retries
• Thinking scheduleTime in past delays execution

5. You need to design a system that processes user signup events by notifying multiple services quickly, but also schedules follow-up tasks with guaranteed retries and delays. Which combination of services should you use?

hard

A. Use only Cloud Tasks for both notifications and follow-ups

B. Use only Pub/Sub with delayed message delivery

C. Use Cloud Functions triggered by HTTP for all processing

D. Use Pub/Sub for notifications and Cloud Tasks for follow-up tasks

Solution

1. Step 1: Identify service for quick multi-subscriber notifications

   Pub/Sub is ideal for sending events quickly to multiple subscribers asynchronously.

2. Step 2: Identify service for scheduled, reliable task execution

   Cloud Tasks provides control over retries, delays, and guaranteed execution for follow-up work.

3. Step 3: Combine services for best fit

   Use Pub/Sub to notify many services fast, and Cloud Tasks to manage follow-up tasks with retries and delays.

4. Final Answer:

   Use Pub/Sub for notifications and Cloud Tasks for follow-up tasks -> Option D

5. Quick Check:

   Pub/Sub for events + Cloud Tasks for reliable tasks [OK]

Hint: Combine Pub/Sub for events and Cloud Tasks for retries/delays [OK]

Common Mistakes:

• Trying to use Pub/Sub for delayed retries
• Using Cloud Tasks for broad event broadcasting
• Ignoring retry guarantees needed for follow-ups