Pub/Sub with Cloud Functions integration in GCP - Mini Project: Build & Apply

Pub/Sub with Cloud Functions integration

📖 Scenario: You are building a simple notification system on Google Cloud Platform. When a message is published to a Pub/Sub topic, a Cloud Function should automatically trigger and process the message.

🎯 Goal: Create a Pub/Sub topic, configure a Cloud Function that triggers on messages published to this topic, and set the function to log the message data.

📋 What You'll Learn

Create a Pub/Sub topic named notifications-topic.

Create a Cloud Function named processNotification triggered by notifications-topic.

The Cloud Function should log the message data received from Pub/Sub.

💡 Why This Matters

🌍 Real World

Pub/Sub with Cloud Functions is commonly used to build event-driven systems where messages trigger automated processing, such as notifications, data pipelines, or alerts.

💼 Career

Understanding how to integrate Pub/Sub with Cloud Functions is essential for cloud developers and engineers working on scalable, serverless architectures on Google Cloud Platform.

1

Create the Pub/Sub topic

Create a Pub/Sub topic named notifications-topic using the gcloud command-line tool.

GCP

# Use the gcloud command to create the Pub/Sub topic
# Your code here

Hint

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

2

Create the Cloud Function configuration

Create a Cloud Function named processNotification that triggers on the Pub/Sub topic notifications-topic. Use the runtime python39 and specify the entry point as process_notification.

GCP

gcloud pubsub topics create notifications-topic
# Use the gcloud command to deploy the Cloud Function with the correct trigger and runtime
# Your code here

Hint

Use gcloud functions deploy with the --trigger-topic flag and specify the runtime and entry point.

3

Write the Cloud Function code

Write the Python function process_notification that takes event and context parameters and logs the Pub/Sub message data decoded as UTF-8.

GCP

gcloud pubsub topics create notifications-topic
gcloud functions deploy processNotification --runtime python39 --trigger-topic notifications-topic --entry-point process_notification --quiet

def process_notification(event, context):
    # Your code here

Hint

Use base64.b64decode to decode the message data and print to log it.

4

Finalize Cloud Function deployment

Update the Cloud Function deployment to include the source code file named main.py containing the process_notification function.

GCP

gcloud pubsub topics create notifications-topic
gcloud functions deploy processNotification --runtime python39 --trigger-topic notifications-topic --entry-point process_notification --quiet

def process_notification(event, context):
    import base64
    message = base64.b64decode(event['data']).decode('utf-8')
    print(f"Received message: {message}")

# Redeploy the function specifying the source file
# Your code here

Hint

Use the --source . flag to specify the current directory containing main.py.

Practice

1.

What is the main role of Google Cloud Pub/Sub when integrated with Cloud Functions?

easy

A. To send messages that trigger Cloud Functions automatically

B. To store large files for Cloud Functions to process

C. To provide a user interface for Cloud Functions

D. To manage user authentication for Cloud Functions

Solution

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

   Pub/Sub is designed to send messages between parts of an app, acting as a messenger.

2. Step 2: Connect Pub/Sub with Cloud Functions

   Cloud Functions run code automatically when they receive messages from Pub/Sub.

3. Final Answer:

   To send messages that trigger Cloud Functions automatically -> Option A

4. Quick Check:

   Pub/Sub triggers Cloud Functions [OK]

Hint: Pub/Sub sends messages; Cloud Functions react to them [OK]

Common Mistakes:

• Thinking Pub/Sub stores files
• Confusing Pub/Sub with UI or authentication
• Assuming Cloud Functions manage user login

2.

Which of the following is the correct way to specify a Pub/Sub trigger in a Cloud Function deployment command?

gcloud functions deploy myFunction --trigger-?

easy

A. --trigger-http my-topic

B. --trigger-bucket my-topic

C. --trigger-topic my-topic

D. --trigger-event my-topic

Solution

1. Step 1: Identify the trigger type for Pub/Sub

   Pub/Sub triggers require specifying the topic name with --trigger-topic.

2. Step 2: Match the correct flag

   --trigger-topic is the correct flag; others relate to storage or HTTP triggers.

3. Final Answer:

   --trigger-topic my-topic -> Option C

4. Quick Check:

   Pub/Sub trigger uses --trigger-topic [OK]

Hint: Pub/Sub triggers use --trigger-topic flag [OK]

Common Mistakes:

• Using --trigger-bucket which is for Cloud Storage
• Using --trigger-http which is for HTTP triggers
• Confusing event triggers with topic triggers

3.

Given this Cloud Function code triggered by Pub/Sub messages, what will be logged when a message with data "Hello" is published?

def hello_pubsub(event, context):
    import base64
    message = base64.b64decode(event['data']).decode('utf-8')
    print(f"Received message: {message}")

medium

A. Received message: event['data']

B. Received message: Hello

C. Received message: b'Hello'

D. Error: 'data' key missing

Solution

1. Step 1: Decode the Pub/Sub message data

   The message data is base64 encoded; decoding it gives the original string "Hello".

2. Step 2: Print the decoded message

   The print statement outputs "Received message: Hello" exactly.

3. Final Answer:

   Received message: Hello -> Option B

4. Quick Check:

   Base64 decode then print = Received message: Hello [OK]

Hint: Decode base64 data to get original message [OK]

Common Mistakes:

• Printing raw base64 bytes instead of decoded string
• Using event['data'] directly without decoding
• Assuming 'data' key is missing

4.

What is the likely cause if a Cloud Function triggered by Pub/Sub never runs after publishing messages?

medium

A. The Cloud Function is not subscribed to the correct Pub/Sub topic

B. The Cloud Function code has a syntax error

C. The Pub/Sub topic does not exist

D. The Cloud Function has too much memory allocated

Solution

1. Step 1: Check the Cloud Function trigger configuration

   If the function is not subscribed to the right topic, it won't receive messages.

2. Step 2: Rule out other causes

   Syntax errors cause deployment failure, not silent no-run; topic existence is needed but usually checked; memory size doesn't stop triggers.

3. Final Answer:

   The Cloud Function is not subscribed to the correct Pub/Sub topic -> Option A

4. Quick Check:

   Wrong topic subscription = no trigger [OK]

Hint: Check topic subscription if function never runs [OK]

Common Mistakes:

• Assuming syntax error causes silent no-run
• Ignoring topic existence or permissions
• Blaming memory size for trigger issues

5.

You want to build a system where multiple Cloud Functions react independently to the same Pub/Sub messages. What is the best way to set this up?

hard

A. Publish messages multiple times to different topics

B. Create multiple Pub/Sub topics, each with one Cloud Function subscription

C. Use one Cloud Function that calls other functions internally

D. Create one Pub/Sub topic and multiple subscriptions, each triggering a different Cloud Function

Solution

1. Step 1: Understand Pub/Sub fan-out pattern

   One topic can have multiple subscriptions; each subscription can trigger a different Cloud Function independently.

2. Step 2: Compare options

   Multiple topics add complexity; one function calling others is indirect; publishing multiple times is inefficient.

3. Final Answer:

   Create one Pub/Sub topic and multiple subscriptions, each triggering a different Cloud Function -> Option D

4. Quick Check:

   One topic, many subscriptions = multiple triggers [OK]

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

Common Mistakes:

• Creating many topics unnecessarily
• Using one function to call others instead of triggers
• Publishing duplicate messages to multiple topics