In the K8s documentation the following source range is hardcoded: 130.211.0.0/22. Is this a fixed one or can I get it using some command (e.g. gcloud, kubectl)?
I have tried to inspect the K8s objects but I don't find a this source range in order to create the firewall rule pointed out in the documentation.
That source IP range (130.211.0.0/22) is a fixed, global value that the GCE L7 load balancer will use when issuing health checks. You can read more about it here.
The source IPs for GCE L7 LB have now been updated to include 35.191.0.0/16. The full list of source ranges is now 35.191.0.0/16, 130.211.0.0/22. (See documentation.)