Why messaging matters in GCP - See It in Action

Why messaging matters

📖 Scenario: You are working on a cloud application that needs to send messages between different parts of the system reliably. Messaging helps different services talk to each other without losing information.

🎯 Goal: Build a simple Google Cloud Pub/Sub setup with a topic and a subscription to understand how messaging works in cloud infrastructure.

📋 What You'll Learn

Create a Pub/Sub topic named my-topic

Create a subscription named my-subscription to my-topic

Configure the subscription to use pull delivery type

Ensure the setup follows Google Cloud best practices for messaging

💡 Why This Matters

🌍 Real World

Messaging systems like Pub/Sub help cloud services communicate reliably without losing messages, even if parts of the system are busy or offline.

💼 Career

Understanding messaging is key for cloud architects and developers to build scalable, decoupled applications that handle data and events efficiently.

1

Create a Pub/Sub topic

Create a Pub/Sub topic named my-topic using the Google Cloud SDK command gcloud pubsub topics create my-topic.

GCP

# Run the command to create the topic
# Your code here

Hint

Use the gcloud pubsub topics create command followed by the topic name.

2

Create a subscription to the topic

Create a subscription named my-subscription to the topic my-topic using the command gcloud pubsub subscriptions create my-subscription --topic=my-topic --ack-deadline=10.

GCP

gcloud pubsub topics create my-topic
# Run the command to create the subscription
# Your code here

Hint

Use gcloud pubsub subscriptions create with the --topic flag to link the subscription.

3

Configure subscription for pull delivery

Ensure the subscription my-subscription is configured for pull delivery by adding the flag --message-retention-duration=600s to the subscription creation command.

GCP

gcloud pubsub topics create my-topic
# Update the subscription creation command to include message retention duration
# Your code here

Hint

Add --message-retention-duration=600s to keep messages for 10 minutes.

4

Verify the Pub/Sub setup

List the topics and subscriptions to verify that my-topic and my-subscription exist using gcloud pubsub topics list and gcloud pubsub subscriptions list.

GCP

gcloud pubsub topics create my-topic
gcloud pubsub subscriptions create my-subscription --topic=my-topic --ack-deadline=10 --message-retention-duration=600s
# Run commands to list topics and subscriptions
# Your code here

Hint

Use gcloud pubsub topics list and gcloud pubsub subscriptions list to check your setup.

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