Cloud functions is a serverless platform for building event based microservices. You write small snippets of code and Google Cloud handles all infrastructure for you. This guide demonstrates how to install a simple cloud function using the google-github-actions/deploy-cloud-functions github action.
Ideally you want to keep your controllers "dumb" and slim. This means that it "should" not have a lot of knowledge of the application's business logic. At Notive, the company I work at, we often use something we like to call "Services".