I'm using a Google Service Account to push MySQL backups from our webserver to Google Drive using a Google API PHP client script setup as a cron job.
I now want to run the same script across multiple webservers, I'm not sure how to correctly configure the service account for this, should I?
Use the same service account and service account key/credentials across all servers?
OR Use the same service account, but add a service account key/credentials for each server?
OR Setup a separate service account for each server?
Your requirements/needs/whatever may vary, but this generally it won't wont matter how you do it.
Create a project on Google developer console, and create a single service account key file and share it across the servers.
Is the same as.
Creating a project on google developer console and creating three separate service account credentials with different key files.
You will be bound by the same quota limits because all are under the same project.
Now if you created three different projects and create a single service account credential for each of the different servers. Then you would see a difference as they are different projects so should be bound by different quota limits.
The Google drive default quota is so high anyway i'm not sure that it really matters what you do.
Even security wise if you have a different file and you were hacked on one server you would't gain or loose anything by the other servers not having the same or different key files.