Exam Cloud Digital Leader topic 1 question 19 discussion

You are a program manager for a team of developers who are building an event-driven application to allow users to follow one another's activities in the app. Each time a user adds himself as a follower of another user, a write occurs in the real-time database.
The developers will develop a lightweight piece of code that can respond to database writes and generate a notification to let the appropriate users know that they have gained new followers. The code should integrate with other cloud services such as Pub/Sub, Firebase, and Cloud APIs to streamline the orchestration process. The application requires a platform that automatically manages underlying infrastructure and scales to zero when there is no activity.
Which primary compute resource should your developers select, given these requirements?