Publishing messages in GCP - Step-by-Step Execution

Process Flow - Publishing messages

Create Topic

↓

Prepare Message

↓

Publish Message to Topic

↓

Message Stored in Topic

↓

Subscribers Receive Message

This flow shows how a message is created, published to a topic, stored, and then delivered to subscribers.

Execution Sample

GCP

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'My message data')
print(future.result())

This code publishes a message to a Google Cloud Pub/Sub topic and waits for confirmation.

Process Table

Step	Action	Input	Result	State Change
1	Create Topic Path	project='my-project', topic='my-topic'	topic_path='projects/my-project/topics/my-topic'	Topic path ready for publishing
2	Prepare Message	Message data='My message data'	Message bytes ready	Message encoded as bytes
3	Publish Message	topic_path, message bytes	Future object returned	Message sent to Pub/Sub service
4	Wait for Result	Future object	Message ID received	Message stored in topic, ready for delivery
5	Message Delivery	Subscribers listening	Subscribers receive message	Message delivered to subscribers

💡 Message published and confirmed with message ID; ready for subscribers.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
publisher	None	PublisherClient instance	PublisherClient instance	PublisherClient instance	PublisherClient instance	PublisherClient instance
topic_path	None	'projects/my-project/topics/my-topic'	'projects/my-project/topics/my-topic'	'projects/my-project/topics/my-topic'	'projects/my-project/topics/my-topic'	'projects/my-project/topics/my-topic'
message_data	None	None	b'My message data'	b'My message data'	b'My message data'	b'My message data'
future	None	None	None	Future object	Future object	Message ID string

Key Moments - 3 Insights

Why do we convert the message to bytes before publishing?

Pub/Sub requires messages as bytes to ensure consistent data format; see execution_table step 2 where message is encoded.

What does the Future object represent after publishing?

The Future object represents the asynchronous result of publishing; it confirms message acceptance when resolved, as shown in step 4.

Does publishing guarantee immediate delivery to subscribers?

Publishing confirms message storage in the topic (step 4), but delivery to subscribers happens asynchronously afterward (step 5).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'topic_path' after step 1?

A 'projects/my-project/topics/my-topic'

B 'my-topic'

C None

D 'my-project'

💡 Hint

Check the 'topic_path' variable in variable_tracker after step 1.

At which step does the message get encoded into bytes?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' and 'Result' columns in execution_table for message preparation.

If the Future object fails to resolve, what happens to the message?

A Message is confirmed published

B Message is lost or not stored

C Message is delivered immediately

D Message is duplicated

💡 Hint

Refer to step 4 in execution_table about waiting for the Future result.

Concept Snapshot

Publishing messages in GCP Pub/Sub:
- Create a topic path with project and topic names
- Prepare message data as bytes
- Publish message asynchronously
- Wait for confirmation via Future
- Message stored and delivered to subscribers asynchronously

Full Transcript

Publishing messages in Google Cloud Pub/Sub involves creating a topic path, preparing the message as bytes, publishing it asynchronously, and waiting for confirmation. Once confirmed, the message is stored in the topic and delivered to subscribers. The Future object returned by the publish method confirms successful storage. Messages must be bytes to ensure consistent format. Delivery to subscribers happens after publishing confirmation.