Possible to route multiple projects to a Cloud Function endpoint?

Question

I have a Saas billing-model and each user has their own GCP Project. This is similar to this reddit thread, which asks:

I’m thinking about selling a saas service. I’ve decided every customer will get their own gcp project every customer will have a bunch of cloud run services, a cloud sql database and some users in Identity platform. I know the default project limit is around 12 and it can be increased by filling a form.

This works for something like BigQuery, where each user's Dataset or Table will be created within their own GCP project, and thus their billing (and data) will be segmented under their project.

However, I also have some shared endpoints on Google Cloud Functions, for example let's say I have general/shared endpoints to do something like "export data". Now of course the query to grab the data will hit the correct GCP project, but if the export (or some other data processing task) is doing something that is very expensive -- some exports might take over an hour to write the data, if dealing with billions of rows, what would be the suggested way to set that up so the end user is paying for their computation, since I imagine an endpoint such as www.example.com/api/export is just going to be on the main Project account, and we wouldn't have, for example, 1000 different cloud functions that do the same thing just to have each one under their respective project.

What might be a solution to this? In a way I'm looking for something like this I suppose where the requestor pays.

Answer 1

You would probably need to record how long each function call took, and save that data somewhere before exiting the shared function.

The only alternative would be to split the function for each client, and use billing labels to help with allocation.