Pub/Sub with Cloud Functions integration in GCP - Step-by-Step Execution

Process Flow - Pub/Sub with Cloud Functions integration

Message Published to Topic

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Pub/Sub Topic Receives Message

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Cloud Function Triggered by Topic

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Cloud Function Executes Code

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Process Message & Perform Action

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Function Completes Execution

A message is sent to a Pub/Sub topic, which triggers a Cloud Function subscribed to that topic. The function runs code to process the message.

Execution Sample

GCP

def pubsub_trigger(event, context):
    message = event['data']
    print(f"Received message: {message}")

This Cloud Function runs when a Pub/Sub message arrives, printing the message content.

Process Table

Step	Event Received	Message Data	Function Action	Output
1	Message published to topic	Hello, Cloud!	Trigger function	Function starts
2	Function triggered	Hello, Cloud!	Decode message	Message decoded
3	Function running	Hello, Cloud!	Print message	Output: Received message: Hello, Cloud!
4	Function completes	Hello, Cloud!	End execution	Function ends

💡 Function completes after processing the Pub/Sub message

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
event['data']	None	Hello, Cloud!	Hello, Cloud!	Hello, Cloud!
message	None	Hello, Cloud!	Hello, Cloud!	Hello, Cloud!

Key Moments - 2 Insights

Why does the function trigger automatically when a message is published?

Because the Cloud Function is configured to listen to the Pub/Sub topic, so any new message triggers it automatically as shown in execution_table step 1 and 2.

What is the format of the message received inside the function?

The message is base64-encoded in the event data, so the function decodes it before use, as seen in execution_table step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the function output at step 3?

A Function starts

B Message decoded

C Output: Received message: Hello, Cloud!

D Function ends

💡 Hint

Check the 'Output' column at step 3 in the execution_table

At which step does the function decode the message data?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Function Action' column in execution_table for decoding

If the message data was empty, what would change in the variable_tracker?

A message variable would be None or empty after step 2

B message variable would still be 'Hello, Cloud!'

C event['data'] would have a value

D No change in variables

💡 Hint

Refer to variable_tracker rows for 'message' and 'event["data"]' values

Concept Snapshot

Pub/Sub sends messages to topics.
Cloud Functions can subscribe to these topics.
When a message arrives, the function triggers automatically.
The function receives event data with the message.
Decode and process the message inside the function.
Function completes after processing.

Full Transcript

In this concept, a message is published to a Pub/Sub topic. This triggers a Cloud Function that is subscribed to that topic. The function receives the event containing the message data, decodes it, and processes it. The execution table shows each step: message publishing, function triggering, decoding, printing the message, and function completion. Variables like 'message' hold the decoded data throughout execution. Key points include automatic triggering by Pub/Sub and decoding the base64 message data. The visual quiz tests understanding of these steps and variable changes.