Which service is used to get notified of changes to Google Cloud resources?

Cloud Pub/Sub is the correct choice for getting notified of changes to Google Cloud resources. This service facilitates the communication between various services and systems by sending messages between them, allowing applications to react to events as they occur. In scenarios where a resource change occurs, such as an update or deletion, Cloud Pub/Sub can publish those events as messages, which can then be received and processed by subscribers.

This capability is crucial for building event-driven architectures, where services need to be immediately informed of changes or updates in real time, thereby enabling automation and responsiveness in cloud applications. By utilizing Cloud Pub/Sub, developers can set up notifications to respond swiftly to changes, improving overall system management and efficiency.

Cloud Firestore, while it allows for real-time data synchronization, is primarily a NoSQL document database and is not designed specifically to notify on changes to all Google Cloud resources. Cloud Functions is a serverless compute service that can execute code in response to events, but it would rely on Cloud Pub/Sub or other triggering mechanisms to handle change notifications. Cloud Audit Logs provides access logs for actions taken on Google Cloud resources but does not actively notify or send messages about changes. Thus, for notifying system changes, Cloud Pub/Sub stands out as the most appropriate solution.