I deployed metric-server. but my "kubectl logs metric-server-pod" gave me this message.

I0813 02:06:46.985836 1 serving.go:312] Generated self-signed cert (apiserver.local.config/certificates/apiserver.crt, apiserver.local.config/certificates/apiserver.key) I0813
02:06:47.348587 1 secure_serving.go:116] Serving securely on [::]:443 E0813 
02:07:00.339450 1 reststorage.go:128] unable to fetch node metrics for node "client-master": no metrics known for node

my kubernetes version :

kubeadm version: &version.Info{
  Major:"1", Minor:"15", 
  GitVersion:"v1.15.0", 
  GitCommit:"e8462b5b5dc2584fdcd18e6bcfe9f1e4d970a529", 
  GitTreeState:"clean", 
  BuildDate:"2019-06-19T16:37:41Z",
  GoVersion:"go1.12.5", 
  Compiler:"gc", 
  Platform:"linux/amd64"
}

sure, I added below options on my metric-server-deployment.yaml

command: 
- /metrics-server 
- --kubelet-insecure-tls 
- --kubelet-preferred-address-types=InternalIP,Hostname,InternalDNS,ExternalDNS,ExternalIP

I use internal network and I installed kubernetes offline please, help me..