This has nothing to do with Stadia. It's open-source software (Agones) designed to run any kind of game server (packaged as a Docker container) on top of Kuber

This has nothing to do with Stadia. It's open-source software (Agones) designed to run any kind of game server (packaged as a Docker container) on top of Kubernetes with easier management around things like scaling, rolling updates, session management, metrics, lifecycle SDK, etc. Google Cloud is just offering a managed version of this on top of GKE. AWS and Azure offer similar platforms and even more products (like AWS Lumberyard game engine).