Topics and subscriptions in GCP - Interactive Code Practice

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'

Amy-subscription

Bmy-topic

Csubscription-1

Dtopic-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a subscription name instead of a topic name

Using a different topic name

The command gcloud pubsub topics create my-topic creates a new Pub/Sub topic named 'my-topic'.

2fill in blank

medium

Complete the code to create a subscription named 'my-subscription' for the topic 'my-topic'.

GCP

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

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

Amy-subscription

Bmy-topic

Ctopic-1

Dsubscription-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the topic name instead of subscription name

Using a different subscription name

The command gcloud pubsub subscriptions create my-subscription --topic=my-topic creates a subscription named 'my-subscription' for the topic 'my-topic'.

3fill in blank

hard

Fix the error in the command 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'

B"Hello"

CHello

Dhello

Attempts:

3 left

💡 Hint

Common Mistakes

Including quotes around the message

Using lowercase message when case matters

The message should be passed without quotes in the command line. So --message=Hello is correct.

4fill in blank

hard

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

GCP

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

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

Amy-subscription

B5

Cmy-topic

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using topic name instead of subscription

Using a non-numeric value for limit

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

5fill in blank

hard

Fill all three blanks to create a push subscription named 'push-sub' for topic 'my-topic' with endpoint 'https://example.com/push'.

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-subscription

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing subscription and topic names

Using incorrect URL format

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

Practice

1. What is the main role of a topic in Google Cloud Pub/Sub?

easy

A. To authenticate users

B. To receive messages from subscribers

C. To store messages permanently

D. To send messages to subscribers

Solution

1. Step 1: Understand the role of a topic

   A topic is where messages are sent or published by a publisher.

2. Step 2: Differentiate topic from subscription

   Subscriptions receive messages from topics, not the other way around.

3. Final Answer:

   To send messages to subscribers -> Option D

4. Quick Check:

   Topic = message sender [OK]

Hint: Topics send; subscriptions receive messages [OK]

Common Mistakes:

• Confusing topic as receiver instead of sender
• Thinking topics store messages permanently
• Mixing roles of topic and subscription

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

easy

A. gcloud pubsub subscriptions create my-sub --topic=my-topic

B. gcloud pubsub topics create my-sub --subscription=my-topic

C. gcloud pubsub subscriptions create my-topic --topic=my-sub

D. gcloud pubsub topics create my-topic --subscription=my-sub

Solution

1. Step 1: Identify correct command syntax

   The command to create a subscription uses subscriptions create with the subscription name and --topic flag for the topic.

2. Step 2: Verify gcloud pubsub subscriptions create my-sub --topic=my-topic matches syntax

   gcloud pubsub subscriptions create my-sub --topic=my-topic correctly uses gcloud pubsub subscriptions create my-sub --topic=my-topic.

3. Final Answer:

   gcloud pubsub subscriptions create my-sub --topic=my-topic -> Option A

4. Quick Check:

   Subscriptions create with --topic flag [OK]

Hint: Subscriptions created with 'subscriptions create' and --topic [OK]

Common Mistakes:

• Using topics create instead of subscriptions create
• Swapping topic and subscription names
• Using --subscription flag instead of --topic

3. Given the following code snippet, what will be printed if the subscription receives a message?

from google.cloud import pubsub_v1

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path('my-project', 'my-sub')

def callback(message):
    print(f'Received: {message.data.decode()}')
    message.ack()

streaming_pull_future = subscriber.subscribe(subscription_path, callback=callback)
print('Listening for messages...')

medium

A. Only Listening for messages...

B. Only Received:

C. Listening for messages... followed by Received:

D. Error because callback is not called

Solution

1. Step 1: Understand code flow

   The code subscribes to a topic and sets a callback to print received messages and acknowledge them.

2. Step 2: Identify output behavior

   It prints 'Listening for messages...' immediately, then prints 'Received: ...' when a message arrives.

3. Final Answer:

   Listening for messages... followed by Received: <message content> -> Option C

4. Quick Check:

   Subscribe prints listening then message received [OK]

Hint: Callback prints message after initial listening print [OK]

Common Mistakes:

• Assuming callback runs before print
• Thinking no output until message arrives
• Ignoring message acknowledgment

4. You created a subscription but messages are not being received. Which of the following is the most likely cause?

medium

A. The subscription is not attached to the correct topic

B. The topic does not exist

C. The subscription name is too long

D. The messages are too large

Solution

1. Step 1: Check subscription-topic link

   If subscription is not linked to the right topic, it won't receive messages.

2. Step 2: Evaluate other options

   Topic existence is important but usually creation fails if topic missing; name length or message size usually cause errors, not silent no messages.

3. Final Answer:

   The subscription is not attached to the correct topic -> Option A

4. Quick Check:

   Subscription-topic mismatch blocks messages [OK]

Hint: Check subscription's topic link first if no messages [OK]

Common Mistakes:

• Ignoring subscription-topic association
• Assuming message size silently blocks delivery
• Thinking subscription name length causes no messages

5. You want to ensure that messages published to a topic are delivered to multiple independent services. Which setup should you use?

hard

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

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

C. Create one subscription and multiple topics linked to it

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

Solution

1. Step 1: Understand message fan-out

   One topic can send messages to many subscriptions, allowing multiple services to receive independently.

2. Step 2: Evaluate options

   Create one topic and multiple subscriptions, one per service uses one topic with multiple subscriptions, which is the recommended pattern for multiple independent consumers.

3. Final Answer:

   Create one topic and multiple subscriptions, one per service -> Option B

4. Quick Check:

   One topic, many subscriptions for multiple services [OK]

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

Common Mistakes:

• Creating multiple topics unnecessarily
• Using one subscription shared by all services
• Linking subscriptions to multiple topics