Cloud Computing, Google Cloud (GCP)

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Scalable Event-Driven Architecture with GCP Pub/Sub

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In today’s fast-paced world, data is generated at an unprecedented rate, and businesses increasingly rely on real-time data processing and event-driven architectures to stay competitive.

Google Cloud Pub/Sub (GCP Pub/Sub) is a robust and scalable messaging service that facilitates real-time data exchange between applications.

In this blog post, we’ll deeply dive into GCP Pub/Sub, exploring its architecture, key components, and the many benefits it offers for businesses.

Introduction to Pub/Sub

Event-driven architecture is becoming increasingly popular as organizations seek to build scalable, responsive, and loosely coupled systems. GCP Pub/Sub is a fundamental component in event-driven architecture. It provides a way for services to communicate asynchronously by exchanging events or messages.

Pub/Sub is a publish/subscribe service: a messaging service where the senders of messages are decoupled from the receivers of messages. Google Cloud Pub/Sub is a fully managed, real-time messaging service that allows you to build applications capable of handling data streams and events. It is designed to provide secure and scalable communication between independently decoupled applications.

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Key Components of Pub/Sub

The Pub/Sub service comprises several key components facilitating asynchronous messaging between different system parts. Here, we’ll explain these key components in detail:

  • Message: At the heart of the Pub/Sub service are messages. A message is the fundamental unit of data that is sent from a publisher to one or more subscribers. It contains the information or payload that needs to be communicated between different parts of an application.
  • Topic: Topics are channels or named entities within the Pub/Sub service. They serve as a way to categorize and organize messages. Publishers send messages to specific topics, and subscribers can subscribe to one or more topics to receive messages of interest. Topics act as the communication channels through which messages flow.
  • Subscription: A subscription represents an interest or connection between a subscriber and a specific topic. When a subscriber wants to receive messages from a particular topic, it creates a subscription to that topic. Subscriptions act as the binding between subscribers and the topics they are interested in. Each subscription retains a copy of the messages sent to the associated topic, allowing multiple subscribers to receive the same messages without interfering with each other.
  • Publisher (Producer): Publishers are the entities responsible for creating messages and sending them to the Pub/Sub service. They publish messages on specific topics. Publishers can be applications, services, sensors, or any source that generates data. They are decoupled from subscribers, meaning they don’t need to know the identity of subscribers or how the messages will be consumed.
  • Subscriber (Consumer): Subscribers are the consumers of messages within the Pub/Sub service. They are applications, services, or devices that want to receive and process messages. Subscribers subscribe to specific topics to indicate their interest in certain messages. Once subscribed, they will receive messages from those topics. Subscribers can be designed to process messages in various ways, depending on the application’s requirements.

Architecture Diagram


Pub/Sub is divided into two primary parts:

  • Control Plane: Responsible for managing the assignment of publishers and subscribers to servers on the data plane.
  • Data Plane: Handles the movement of messages between publishers and subscribers.

The servers are called “routers” in the control plane, while the data plane employs “forwarders”.

Control Plane

The Pub/Sub control plane plays a crucial role in distributing clients to forwarders, aiming to ensure scalability, availability, and low latency for all clients. Each forwarder is equipped to serve clients for any topic or subscription. When a client establishes a connection with Pub/Sub, the router determines the appropriate data centers for the client to connect to based on the shortest network distance, which measures the latency between two points.

The router distributes the overall load evenly across the available forwarders within a specific data center. In doing so, the router must balance two essential goals: (a) maintaining load uniformity and (b) ensuring assignment stability.

The router employs a variation of consistent hashing developed by Google Research to achieve this balance. It furnishes the client with an ordered list of forwarders to which the client can consider connecting. This ordered list may change based on forwarder availability and the load pattern generated by the client.

Upon receiving this list of forwarders, the client connects to one or more. The client typically prefers the forwarders recommended by the router, but it also considers any failures that may have occurred. For example, if multiple attempts to connect to the nearest forwarders have failed, the client might try forwarders in a different data center. To shield Pub/Sub clients from these implementation intricacies, a service proxy stands between the clients and forwarders, handling connection optimization on behalf of clients.

Data Plane

The data plane’s primary function is to receive messages from publishers and transmit them to clients. Let’s delve into the message flow:

  • A publisher dispatches a message.
  • The message is written to storage.
  • Pub/Sub dispatches an acknowledgment to the publisher, confirming receipt of the message and guaranteeing its delivery to all associated subscriptions.
  • Concurrently with storing the message, Pub/Sub delivers it to subscribers.
  • Upon processing the message, subscribers convey an acknowledgment to Pub/Sub.
  • Once at least one subscriber for each subscription has acknowledged the message, Pub/Sub proceeds to remove the message from storage.


  • Scalability: GCP Pub/Sub is designed to handle massive workloads. It automatically scales to accommodate high message volumes, ensuring your applications can handle increased data traffic without manual intervention.
  • Reliability: Google Cloud Pub/Sub guarantees at least one message delivery, meaning your messages won’t be lost, even in network disruptions or service failures. Reliability is vital for applications with critical missions.
  • Durability: Messages sent to Pub/Sub are stored in a highly durable manner. They are replicated across multiple data centers, ensuring your data is safe and available, even during hardware failures or other disasters.
  • Global Reach: Pub/Sub is available in multiple regions, allowing you to deploy your applications closer to your users for reduced latency and better performance. It provides a global distribution of messages to ensure seamless communication.
  • Real-time Data Processing: GCP Pub/Sub is essential for building real-time data pipelines. It facilitates the creation of event-driven architectures, enabling you to respond to events and data changes in real time, which is crucial for applications like fraud detection and analytics.
  • Elasticity and Cost Efficiency: With automatic scaling, you only pay for the resources you use. This elasticity reduces operational costs and ensures you can efficiently handle both peaks and valleys in your data traffic.
  • Integration with Other GCP Services: GCP Pub/Sub seamlessly integrates with other Google Cloud services, such as Cloud Functions, Dataflow, and BigQuery. This makes it a powerful component for building complex data processing pipelines in the Google Cloud ecosystem.
  • Security: GCP Pub/Sub offers strong security features, including Identity and Access Management (IAM) controls, encryption at rest and in transit, and audit logging. You can rest assured that your data remains protected.


In the era of data-driven decision-making, Google Cloud Pub/Sub emerges as a robust messaging service that empowers businesses to build scalable, reliable, and real-time applications. Its architecture, combined with its numerous benefits, makes it a valuable tool for organizations looking to stay ahead in the competitive landscape. By leveraging GCP Pub/Sub, you can establish a solid foundation for creating event-driven, responsive, and data-intensive applications that meet the needs of today’s dynamic world.

Drop a query if you have any questions regarding Google Cloud Pub/Sub and we will get back to you quickly.

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1. What are some best practices for using Google Cloud Pub/Sub?

ANS: – Best practices include setting up monitoring and alerting, handling dead-letter messages, securing access to topics and subscriptions, and using the appropriate Acknowledgment mode.

2. Is Google Cloud Pub/Sub suitable for small businesses, or is it mainly for enterprises?

ANS: – Pub/Sub is suitable for businesses of all sizes. It can scale to meet the needs of both small startups and large enterprises.

WRITTEN BY Rajeshwari B Mathapati

Rajeshwari B Mathapati is working as a Research Associate (WAR and Media Services) at CloudThat. She is Google Cloud Associate certified. She is interested in learning new technologies and writing technical blogs.



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