Google Cloud Messaging Essentials

Introduction

In this lesson, we will explore the core concepts and operations of Google Cloud Pub/Sub, a messaging service that enables reliable, scalable, and asynchronous communication between different parts of your applications. Cloud Pub/Sub is designed around the concepts of topics and subscriptions, allowing you to publish messages to a topic and have them delivered to one or more subscribers . We will cover how to publish messages, configure subscriptions, and manage message delivery and acknowledgment. By the end of this lesson, you will understand how to use this messaging service effectively to build robust and decoupled systems.

Publishing Messages to Topics

To send information through Google Cloud Pub/Sub, you publish messages to a topic. Publishing a message to a Cloud Pub/Sub topic: Pythonfrom google.cloud import pubsub_v1 publisher = pubsub_v1.PublisherClient() topic_path = publisher.topic_path('your-project-id', 'your-topic-name') future = publisher.publish(topic_path, b'Hello world!') print(f'Message published: {future.result()}') Output: textMessage published: 123456789012345678 You can also include custom attributes with your message: Pythonfuture = publisher.publish( topic_path, b'Hello with attributes!', author='John Doe', weeks_on_job='10' ) print(f'Message published: {future.result()}') Output: textMessage published: 123456789012345679

Sending Multiple Messages at a Time

When you need to send multiple messages efficiently, Cloud Pub/Sub supports batch publishing. This allows you to publish several messages in a single request, reducing network overhead and improving throughput. Batch publishing messages to a Cloud Pub/Sub topic: Pythonfrom google.cloud import pubsub_v1 publisher = pubsub_v1.PublisherClient() topic_path = publisher.topic_path('your-project-id', 'your-topic-name') messages = [ (b'This is the content of message 1', {'author': 'Jane Doe'}), (b'This is the content of message 2', {'author': 'John Smith'}), # Add more messages as needed ] futures = [] for data, attrs in messages: future = publisher.publish(topic_path, data, **attrs) futures.append(future) for future in futures: print(f'Message published: {future.result()}') Output: textMessage published: 123456789012345680 Message published: 123456789012345681 Batching is handled automatically by the client library, but you can also configure batching settings for more control if needed.

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Message Delivery and Retrieval

In Cloud Pub/Sub, messages published to a topic are delivered to all subscriptions attached to that topic. There are two main types of subscriptions: pull and push. With pull subscriptions, your application explicitly requests messages from the subscription. With push subscriptions, messages are automatically sent to a specified endpoint.

Pulling messages from a Cloud Pub/Sub subscription:

Python

from google.cloud import pubsub_v1

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path('your-project-id', 'your-subscription-name')

response = subscriber.pull(
    request={
        "subscription": subscription_path,
        "max_messages": 10,
    }
)

for received_message in response.received_messages:
    print(f"Received: {received_message.message.data}")
    print(f"Message ID: {received_message.message.message_id}")
    print(f"Publish time: {received_message.message.publish_time}")
    if received_message.message.attributes:
        print(f"Attributes: {dict(received_message.message.attributes)}")
    # Acknowledge the message after processing
    subscriber.acknowledge(
        request={
            "subscription": subscription_path,
            "ack_ids": [received_message.ack_id],
        }
    )

from google.cloud import pubsub_v1

subscriber = pubsub_v1.SubscriberClient()
subscription_path = subscriber.subscription_path('your-project-id', 'your-subscription-name')

response = subscriber.pull(
    request={
        "subscription": subscription_path,
        "max_messages": 10,
    }
)

for received_message in response.received_messages:
    print(f"Received: {received_message.message.data}")
    print(f"Message ID: {received_message.message.message_id}")
    print(f"Publish time: {received_message.message.publish_time}")
    if received_message.message.attributes:
        print(f"Attributes: {dict(received_message.message.attributes)}")
    # Acknowledge the message after processing
    subscriber.acknowledge(
        request={
            "subscription": subscription_path,
            "ack_ids": [received_message.ack_id],
        }
    )

Output:

text

Received: b'Hello world!'
Message ID: 123456789012345678
Publish time: 2024-01-15 10:30:45.123456+00:00
Received: b'Hello with attributes!'
Message ID: 123456789012345679
Publish time: 2024-01-15 10:30:45.234567+00:00
Attributes: {'author': 'John Doe', 'weeks_on_job': '10'}

Received: b'Hello world!'
Message ID: 123456789012345678
Publish time: 2024-01-15 10:30:45.123456+00:00
Received: b'Hello with attributes!'
Message ID: 123456789012345679
Publish time: 2024-01-15 10:30:45.234567+00:00
Attributes: {'author': 'John Doe', 'weeks_on_job': '10'}

With pull subscriptions, you control when and how many messages you retrieve, and you must acknowledge each message after processing.

Introduction

Publishing Messages to Topics

Sending Multiple Messages at a Time

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Message Delivery and Retrieval

Acknowledging and Deleting Messages

Summary