Cloud Spanner is a global scale SQL database that scales extremely well. That would be the best choice.

The pricing calculator can be used to give clear estimates of resource usage.
-> Running test loads is as closely indicative as using the pricing calculator.
-> There are no cloud cost references published, either by Google or CNCF. Even if some companies have published such info. It might not apply to you.
Reference link:- https://cloud.google.com/products/calculator

You can dynamically increase the size of a subnet in a custom network by expanding the range of IP addresses allocated to it. Doing that doesn't affect already configured VMs.

Kubernetes vs. Docker
Often misunderstood as a choice between one or the other, Kubernetes and Docker are different yet complementary technologies for running containerized applications.
Docker lets you put everything you need to run your application into a box that can be stored and opened when and where it is required. Once you start boxing up your applications, you need a way to manage them; and that's what Kubernetes does.
Kubernetes is a Greek word meaning 'captain' in English. Like the captain is responsible for the safe journey of the ship in the seas, Kubernetes is responsible for carrying and delivering those boxes safely to locations where they can be used.
- Kubernetes can be used with or without Docker.
- Docker is not an alternative to Kubernetes, so it's less of a "Kubernetes vs. Docker" question. It's about using Kubernetes with Docker to containerize your applications and run them at scale.
- The difference between Docker and Kubernetes relates to the role each play in containerizing and running your applications.
- Docker is an open industry standard for packaging and distributing applications in containers.
- Kubernetes uses Docker to deploy, manage, and scale containerized applications.