Cloud Pubsub | Google Iot | Googlecloud Tutorial

Introduction

Cloud Pub/Sub is a messaging service provided by Google Cloud that enables you to send and receive messages between independent applications. It is designed to provide reliable, many-to-many, asynchronous messaging between decoupled systems.

Setting Up Cloud Pub/Sub

To get started with Cloud Pub/Sub, you need a Google Cloud project. Follow these steps:

Step 1: Create a new project in the Google Cloud Console.

Step 2: Enable the Cloud Pub/Sub API for your project.

Step 3: Set up authentication by creating a service account and downloading the JSON key file.

Creating a Topic

A topic is a named resource to which messages are sent by publishers. To create a topic, use the following command:

gcloud pubsub topics create my-topic

Created topic [projects/YOUR_PROJECT_ID/topics/my-topic].

Publishing Messages

Publish messages to the topic using the following command:

gcloud pubsub topics publish my-topic --message "Hello, World!"

messageIds: 123456789012345

Creating a Subscription

A subscription is a named resource representing the stream of messages from a single, specific topic, to be delivered to the subscribing application. To create a subscription, use the following command:

gcloud pubsub subscriptions create my-subscription --topic my-topic

Created subscription [projects/YOUR_PROJECT_ID/subscriptions/my-subscription].

Receiving Messages

Receive messages from the subscription using the following command:

gcloud pubsub subscriptions pull my-subscription --auto-ack

┌──────────────────────┬───────────────┐
│ DATA │ MESSAGE_ID │
├──────────────────────┼───────────────┤
│ Hello, World! │ 1234567890123 │
└──────────────────────┴───────────────┘

Example Application

Here's a simple example of a Python application that publishes and receives messages using Cloud Pub/Sub:

Publisher (publish.py):

import os
from google.cloud import pubsub_v1

os.environ["GOOGLE_APPLICATION_CREDENTIALS"] = "path/to/your/service-account-file.json"

publisher = pubsub_v1.PublisherClient()
topic_path = publisher.topic_path('YOUR_PROJECT_ID', 'my-topic')

data = 'Hello, World!'
data = data.encode('utf-8')
future = publisher.publish(topic_path, data)
print(f'Published message ID: {future.result()}')

Subscriber (subscribe.py):

import os
from google.cloud import pubsub_v1

os.environ["GOOGLE_APPLICATION_CREDENTIALS"] = "path/to/your/service-account-file.json"

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path('YOUR_PROJECT_ID', 'my-subscription')

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

subscriber.subscribe(subscription_path, callback=callback)

print('Listening for messages on {}'.format(subscription_path))
while True:
    pass

Conclusion

Cloud Pub/Sub is a powerful tool for building scalable and reliable messaging systems. By following this tutorial, you should now have a good understanding of how to create topics and subscriptions, publish and receive messages, and implement a simple application using Cloud Pub/Sub.

Comprehensive Guide to Cloud Pub/Sub