Kubernetes monitoring metrics server doesn't start

Question

I have a kubeadm Kubernetes Cluster with One Master and Worker Node.

I am trying to install the Kubernetes metrics server but nothing will be collected. The message inside the metrics server is:

17:11:08.680724 1 serving.go:341] Generated self-signed cert (/tmp/apiserver.crt, /tmp/apiserver.key)
I1122 17:11:09.439494 1 requestheader_controller.go:169] Starting RequestHeaderAuthRequestController
I1122 17:11:09.439529 1 shared_informer.go:240] Waiting for caches to sync for RequestHeaderAuthRequestController
I1122 17:11:09.439559 1 configmap_cafile_content.go:202] Starting client-ca::kube-system::extension-apiserver-authentication::client-ca-file
I1122 17:11:09.439574 1 configmap_cafile_content.go:202] Starting client-ca::kube-system::extension-apiserver-authentication::requestheader-client-ca-file
I1122 17:11:09.439585 1 shared_informer.go:240] Waiting for caches to sync for client-ca::kube-system::extension-apiserver-authentication::client-ca-file
I1122 17:11:09.439589 1 shared_informer.go:240] Waiting for caches to sync for client-ca::kube-system::extension-apiserver-authentication::requestheader-client-ca-file
I1122 17:11:09.439880 1 dynamic_serving_content.go:130] Starting serving-cert::/tmp/apiserver.crt::/tmp/apiserver.key
I1122 17:11:09.440065 1 secure_serving.go:197] Serving securely on [::]:4443
I1122 17:11:09.440599 1 tlsconfig.go:240] Starting DynamicServingCertificateController
I1122 17:11:09.540590 1 shared_informer.go:247] Caches are synced for client-ca::kube-system::extension-apiserver-authentication::client-ca-file
I1122 17:11:09.540672 1 shared_informer.go:247] Caches are synced for client-ca::kube-system::extension-apiserver-authentication::requestheader-client-ca-file
I1122 17:11:09.540722 1 shared_informer.go:247] Caches are synced for RequestHeaderAuthRequestController

If I am trying kubectl top node then I am getting following issue:

W1122 19:36:25.770078    4684 top_node.go:119] Using json format to get metrics. Next release will switch to protocol-buffers, switch early by passing --use-protocol-buffers flag
Error from server (ServiceUnavailable): the server is currently unable to handle the request (get nodes.metrics.k8s.io)

These are my kubernetes files:

apiVersion: v1
kind: ServiceAccount
metadata:
  labels:
    k8s-app: metrics-server
  name: metrics-server
  namespace: kube-system
---


apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  labels:
    k8s-app: metrics-server
  name: system:metrics-server
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin
subjects:
- kind: ServiceAccount
  name: metrics-server
  namespace: kube-system
---
apiVersion: v1
kind: Service
metadata:
  labels:
    k8s-app: metrics-server
  name: metrics-server
  namespace: kube-system
spec:
  ports:
  - name: https
    port: 443
    protocol: TCP
    targetPort: https
  selector:
    k8s-app: metrics-server
---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    k8s-app: metrics-server
  name: metrics-server
  namespace: kube-system
spec:
  selector:
    matchLabels:
      k8s-app: metrics-server
  strategy:
    rollingUpdate:
      maxUnavailable: 0
  template:
    metadata:
      labels:
        k8s-app: metrics-server
    spec:
      containers:
      - args:
        - --cert-dir=/tmp
        - --secure-port=4443
        - --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
        - --kubelet-use-node-status-port
        - --kubelet-insecure-tls=true
        - --metric-resolution=15s
        image: k8s.gcr.io/metrics-server/metrics-server:v0.5.0
        imagePullPolicy: IfNotPresent
        name: metrics-server


        securityContext:
          readOnlyRootFilesystem: true
          runAsNonRoot: true
          runAsUser: 1000
        volumeMounts:
        - mountPath: /tmp
          name: tmp-dir
      nodeSelector:
        kubernetes.io/os: linux
      priorityClassName: system-cluster-critical
      serviceAccountName: metrics-server
      volumes:
      - emptyDir: {}
        name: tmp-dir
---
apiVersion: apiregistration.k8s.io/v1
kind: APIService
metadata:
  labels:
    k8s-app: metrics-server
  name: v1beta1.metrics.k8s.io
spec:
  group: metrics.k8s.io
  groupPriorityMinimum: 100
  insecureSkipTLSVerify: true
  service:
    name: metrics-server
    namespace: kube-system
  version: v1beta1
  versionPriority: 100

Answer 1

The issue was that the metrics server was not scheduled on Master Node. Therefore, I added to the Metrics Server Deployment a toleration and Node scheduler:

      affinity: 
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key:  node-role.kubernetes.io/master
                operator: In
                values:
                  - ""
      tolerations:
        - key: node-role.kubernetes.io/master
          operator: Equal
          effect: NoSchedule
          value:  ""
        - key: node.kubernetes.io/disk-pressure
          operator: Equal
          effect: NoSchedule
          value:  ""