Which Google Cloud Platform floating IP address pattern maps to my use case?

In this option, "keepalived or other scripts use API calls to add a route to a new healthy instance or remove a route from an unhealthy instance.

"This approach is useful in situations where you can't use Compute Engine health checks to track the health of the application or determine which virtual machine is primary. Any application logic can trigger dynamic reprogramming of routes."

Failover using routes API calls