Why messaging matters in GCP - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Pub/Sub topic named 'my-topic'.

GCP

gcloud pubsub topics create [1]

Drag options to blanks, or click blank then click option'

Adefault-topic

Btopic-1

Ctest-topic

Dmy-topic

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different topic name than 'my-topic'.

The command creates a Pub/Sub topic named 'my-topic'. This is the first step to enable messaging.

2fill in blank

medium

Complete the code to publish a message 'Hello' to the topic 'my-topic'.

GCP

gcloud pubsub topics publish my-topic --message=[1]

Drag options to blanks, or click blank then click option'

A"Hello World"

B"Message"

C"Hello"

D"Hi"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different message text.

Missing quotes around the message.

The message 'Hello' is published to the topic 'my-topic'. Quotes are needed around the message.

3fill in blank

hard

Fix the error in the command to subscribe to 'my-topic' with subscription name 'my-sub'.

GCP

gcloud pubsub subscriptions create [1] --topic=my-topic

Drag options to blanks, or click blank then click option'

Amy-sub

Bmy-subscription

Cmy-topic

Dsubscription-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the topic name as subscription name.

Using a different subscription name.

The subscription name should be 'my-sub' as specified. Using the topic name or other names causes errors.

4fill in blank

hard

Fill both blanks to pull messages from subscription 'my-sub' and acknowledge them.

GCP

gcloud pubsub subscriptions pull [1] --auto-ack --limit=[2]

Drag options to blanks, or click blank then click option'

Amy-sub

B5

C10

Dmy-topic

Attempts:

3 left

💡 Hint

Common Mistakes

Using topic name instead of subscription name.

Using a limit number too large or unrelated.

The command pulls 5 messages from subscription 'my-sub' and acknowledges them automatically.

5fill in blank

hard

Fill all three blanks to create a push subscription named 'push-sub' for topic 'my-topic' with endpoint URL.

GCP

gcloud pubsub subscriptions create [1] --topic=[2] --push-endpoint=[3]

Drag options to blanks, or click blank then click option'

Apush-sub

Bmy-topic

Chttps://example.com/push

Dmy-sub

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing subscription and topic names.

Using invalid or missing endpoint URL.

This command creates a push subscription named 'push-sub' for the topic 'my-topic' with the given HTTPS endpoint.

Practice

1. Why is messaging important in cloud systems like Google Cloud Pub/Sub?

easy

A. It stores large files permanently.

B. It speeds up the internet connection.

C. It replaces the need for databases.

D. It allows different parts of a system to communicate reliably.

Solution

1. Step 1: Understand messaging role in cloud systems

   Messaging enables components to send and receive information without direct connection, ensuring reliable communication.

2. Step 2: Identify the correct purpose of messaging

   Messaging is not about speeding internet, storing files, or replacing databases but about reliable communication.

3. Final Answer:

   It allows different parts of a system to communicate reliably. -> Option D

4. Quick Check:

   Messaging = Reliable communication [OK]

Hint: Messaging means reliable communication between system parts [OK]

Common Mistakes:

• Confusing messaging with file storage
• Thinking messaging speeds up internet
• Assuming messaging replaces databases

2. Which of the following is the correct way to create a Pub/Sub topic using gcloud CLI?

easy

A. gcloud pubsub topics create my-topic

B. gcloud create pubsub topic my-topic

C. gcloud pubsub create topic my-topic

D. gcloud topic pubsub create my-topic

Solution

1. Step 1: Recall gcloud Pub/Sub topic creation syntax

   The correct command is 'gcloud pubsub topics create [TOPIC_NAME]'.

2. Step 2: Match the command to options

   Only gcloud pubsub topics create my-topic matches the correct syntax exactly.

3. Final Answer:

   gcloud pubsub topics create my-topic -> Option A

4. Quick Check:

   Correct gcloud topic creation command = gcloud pubsub topics create my-topic [OK]

Hint: Remember: 'gcloud pubsub topics create' is the syntax [OK]

Common Mistakes:

• Mixing order of words in command
• Using 'create pubsub topic' instead of 'pubsub topics create'
• Omitting 'topics' keyword

3. Given this Pub/Sub setup code snippet, what will be the output if a message is published successfully?

from google.cloud import pubsub_v1
publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path('my-project', 'my-topic')
future = publisher.publish(topic_path, b'Hello World')
print(future.result())

medium

A. The message ID string confirming successful publish

B. An error message about missing credentials

C. None, because publish is asynchronous

D. The content of the message 'Hello World'

Solution

1. Step 1: Understand publish method behavior

   The publish method returns a future that resolves to a message ID string when successful.

2. Step 2: Analyze the print statement

   Calling future.result() waits for completion and returns the message ID, not the message content.

3. Final Answer:

   The message ID string confirming successful publish -> Option A

4. Quick Check:

   future.result() returns message ID [OK]

Hint: future.result() returns message ID, not message content [OK]

Common Mistakes:

• Thinking publish returns message content
• Assuming publish is fully synchronous without future
• Confusing error output with success

4. You wrote this code to subscribe to a Pub/Sub topic but get no messages:

from google.cloud import pubsub_v1
subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path('my-project', 'my-subscription')
def callback(message):
    print(f'Received: {message.data}')
    message.ack()
subscriber.subscribe(subscription_path, callback=callback)

What is the likely problem?

medium

A. The subscriber client is not initialized correctly.

B. The callback function is missing the message.ack() call.

C. The subscription does not exist or is not attached to the topic.

D. The topic name is incorrect in the subscription path.

Solution

1. Step 1: Check subscription existence and linkage

   If the subscription does not exist or is not linked to the topic, no messages will be received.

2. Step 2: Verify other code parts

   The callback acknowledges messages correctly, subscriber client is initialized properly, and subscription path uses correct subscription name.

3. Final Answer:

   The subscription does not exist or is not attached to the topic. -> Option C

4. Quick Check:

   Missing or unlinked subscription = no messages [OK]

Hint: Check subscription exists and links to topic first [OK]

Common Mistakes:

• Forgetting to create subscription before subscribing
• Assuming callback runs without subscription
• Mixing topic and subscription names

5. You want to build a system where multiple services process messages independently but reliably from the same stream of events. Which Pub/Sub feature best supports this?

hard

A. Use Cloud Storage instead of Pub/Sub for message sharing.

B. Create multiple subscriptions on the same topic for each service.

C. Publish messages to different topics for each service.

D. Use a single subscription and share it among all services.

Solution

1. Step 1: Understand message delivery to multiple consumers

   Pub/Sub allows multiple subscriptions on one topic, so each service can get all messages independently.

2. Step 2: Evaluate options for independent processing

   Sharing one subscription means messages are load balanced, not duplicated; publishing to different topics duplicates effort; Cloud Storage is not for messaging.

3. Final Answer:

   Create multiple subscriptions on the same topic for each service. -> Option B

4. Quick Check:

   Multiple subscriptions = independent reliable processing [OK]

Hint: Use multiple subscriptions on one topic for independent consumers [OK]

Common Mistakes:

• Using one subscription shared by all services
• Publishing to separate topics unnecessarily
• Confusing storage with messaging service