I speculate it's just containers, repurposed solely for the purposes of serving HTTP APIs.
When you "deploy" a cloud function I think it means it rebuilds the container image and replaces the running instance of the container.
I imagine that e.g. the usual 60s "timeout" of a cloud function just means they kill the container after 60s?
And maybe e.g. Firestore triggers means that Firestore maintains event handlers that spawn a container (your "trigger") to run the code you want for that event?
