As I understand from official Kubernetes documentation, the API server is supposed to run on the master.
But in the config file obtained from the cluster’s page on Rancher UI, I see the address of the Rancher Server in clusters > cluster > server. There is a second entry with IP of the master node of the cluster. The second entry is expected but the first one is not.
Also, what happens to the cluster if Rancher server goes down?
So the kube API server runs on all control plane nodes and you can access it directly. The Rancher server also provides a proxied connection via the cattle-cluster-agent pod as well.
So if Rancher is down/unavailable you can still access your cluster by pointing your kube Config directly to one of cp nodes.
Also, you can manually generate a kubeconfig using the script https://github.com/patrick0057/kubecert in the event Rancher is down.