Have you actually done this, or are you repeating stuff off the website? Because everyone I've talked with about kubernetes federation says it's really not ready for production use.
The approach we have taken is to create independent clusters with a common LoadBalancer.
Basically, the LB decides which kubernetes cluster will serve your request and once you're in a k8s cluster, you stay there.
You don't have the control-plane that the federation provides and a bit of overhead managing clusters independently, but we have automated the majority of the process. On the other hand, debugging is way easier and we don't suffer from weird latencies between clusters (weird because sometimes a request will go to a different cluster without any apparent reason <-- I'm sure there's one, but none that you could see/expect, hence debugging).
My people's time is more important than your complex system.
Basically, the LB decides which kubernetes cluster will serve your request and once you're in a k8s cluster, you stay there.
You don't have the control-plane that the federation provides and a bit of overhead managing clusters independently, but we have automated the majority of the process. On the other hand, debugging is way easier and we don't suffer from weird latencies between clusters (weird because sometimes a request will go to a different cluster without any apparent reason <-- I'm sure there's one, but none that you could see/expect, hence debugging).
My people's time is more important than your complex system.