What is the purpose of adding a subscription to a topic in Cloud Pub/Sub?
The purpose of adding a subscription to a topic in Cloud Pub/Sub is to enable the delivery of messages published to the topic to interested subscribers. Cloud Pub/Sub is a messaging service provided by Google Cloud Platform (GCP) that allows decoupled and asynchronous communication between applications. It provides reliable, scalable, and durable messaging capabilities that can be used to build distributed systems, event-driven architectures, and real-time data processing pipelines.
When a subscription is added to a topic in Cloud Pub/Sub, it establishes a communication channel between the topic and the subscriber. The subscriber can be any application or service that wants to receive messages published to the topic. This decoupled architecture enables loose coupling between publishers and subscribers, allowing them to evolve independently without direct dependencies on each other.
Subscriptions in Cloud Pub/Sub can be configured with different delivery options, such as push or pull. With a push subscription, Cloud Pub/Sub actively sends messages to a pre-configured endpoint, typically an HTTP/HTTPS endpoint, specified by the subscriber. This allows the subscriber to receive messages in near real-time. On the other hand, with a pull subscription, the subscriber actively polls the Cloud Pub/Sub service to retrieve messages at its own pace. This mode is suitable for subscribers that can handle intermittent or batch processing of messages.
Adding a subscription to a topic in Cloud Pub/Sub provides several benefits. Firstly, it enables the decoupling of publishers and subscribers, allowing them to scale independently and evolve without impacting each other. For example, if a new subscriber needs to be added to receive messages from a topic, it can simply create a new subscription without requiring any changes to the existing publishers.
Secondly, Cloud Pub/Sub ensures reliable and durable message delivery. It guarantees at-least-once delivery semantics, meaning that messages published to a topic will be delivered to subscribers at least once. It also provides message ordering within a topic, ensuring that messages are delivered to subscribers in the order they were published. This is particularly useful in scenarios where message ordering is critical, such as event sourcing or processing time-series data.
Thirdly, Cloud Pub/Sub is highly scalable and can handle large volumes of messages with low latency. It can handle millions of messages per second, making it suitable for high-throughput applications. The underlying infrastructure of Cloud Pub/Sub is designed to be globally distributed, ensuring low latency message delivery across different regions.
Adding a subscription to a topic in Cloud Pub/Sub enables the delivery of messages published to the topic to interested subscribers. It provides decoupled and asynchronous communication, reliable and durable message delivery, and scalability for handling large volumes of messages.
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