Kubernetes: Nodes/Pods not showing with kubectl after building cluster with kubeadm

Question

I am trying to create a Kubernetes cluster using kubeadm tool. For this I installed the supported docker version as specified here

I could also install kubeadm successfully. I initiated the cluster with below command

 sudo kubeadm init --pod-network-cidr=10.244.0.0/14 --apiserver-advertise-address=172.16.0.11

and I got the message to use kubeadm join to join the cluster as shown below

 Your Kubernetes control-plane has initialized successfully!

 To start using your cluster, you need to run the following as a regular user:

 mkdir -p $HOME/.kube
 sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
 sudo chown $(id -u):$(id -g) $HOME/.kube/config

 You should now deploy a pod network to the cluster.
 Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:
 https://kubernetes.io/docs/concepts/cluster-administration/addons/

 Then you can join any number of worker nodes by running the following on each as root:

 kubeadm join 172.16.0.11:6443 --token ptdibx.r2uu0s772n6fqubc \
--discovery-token-ca-cert-hash sha256:f3e36a8e82fb8166e0faf407235f12e256daf87d0a6d0193394f4ce31b50255c   

Used flannel for networking purpose

  $ kubectl apply -f    https://raw.githubusercontent.com/coreos/flannel/2140ac876ef134e0ed5af15c65e414cf26827915/Documentation/kube-flannel.yml
  podsecuritypolicy.policy/psp.flannel.unprivileged created
  clusterrole.rbac.authorization.k8s.io/flannel created
  clusterrolebinding.rbac.authorization.k8s.io/flannel created
  serviceaccount/flannel created
  configmap/kube-flannel-cfg created
  daemonset.apps/kube-flannel-ds-amd64 created
  daemonset.apps/kube-flannel-ds-arm64 created

After that when I try to check the kubectl command to check the pods/nodes status it fails

   $ sudo kubectl get nodes
   error: no configuration has been provided, try setting KUBERNETES_MASTER environment variable

   $ sudo kubectl get pods --all-namespaces
   error: no configuration has been provided, try setting KUBERNETES_MASTER environment variable

   $ echo $KUBECONFIG 
   /etc/kubernetes/admin.conf:/home/ltestzaman/.kube/config

Docker and kubernetes version are as follows:

    $ sudo kubeadm version
    kubeadm version: &version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.2",      
    GitCommit:"52c56ce7a8272c798dbc29846288d7cd9fbae032", GitTreeState:"clean",  
     BuildDate:"2020-04-16T11:54:15Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}

   $ sudo docker version
   Client:
   Version:      17.03.0-ce
   API version:  1.26
   Go version:   go1.7.5
   Git commit:   3a232c8
   Built:        Tue Feb 28 08:10:07 2017
   OS/Arch:      linux/amd64

   Server:
   Version:      17.03.0-ce

How to make the cluster work?

Output of admin.conf is as follows:

$ sudo cat /etc/kubernetes/admin.conf
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0tLS0tCk1JSUN5RENDQWJDZ0F3SUJBZ0lCQURBTkJna3Foa2lHOXcwQkFRc0ZBREFWTVJNd0VRWURWUVFERXdwcmRXSmwKY201bGRHVnpN
QjRYRFRJd01EUXhPREV6TlRnek1sb1hEVE13TURReE5qRXpOVGd6TWxvd0ZURVRNQkVHQTFVRQpBeE1LYTNWaVpYSnVaWFJsY3pDQ0FTSXdEUVlKS29aSWh2Y05BUUVCQlFBRGdnRVBBRENDQVFvQ2dnRUJBSjdvCnhERGVP
UWd4TGsyWE05K0pxc0hYRkRPWHB2YXYxdXNyeXNYMldOZzlOOVFaeDVucFA2UTRpYkQrZDFjWFcyL0oKY0ZXUjhBSDliaG5hZlhLRUhiUVZWT0R2UTcwbFRmNXVtVlQ4Qk5ZUjRQTmlCWjFxVDNMNnduWlYrekl6a0ZKMwp0
eVVNK0prUy80K2dMazI3b01HMFZ4Rnpjd1ozREMxWEFqRXVxb3FrYVF5UGUzMk9XZmZ2N082TjhxeWNCNkdnClNxbWxNWldBMk1DL0J1cFpZWXRYNkUyYUtNUloxZjkzRlpCaFdYNG9DYjVQSGdSUEdoNTFiNERKZExoYlk4
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K2g1U09Ddms1YncwbEYKODhZNnlTaHk3U1B6amRNUHdRcks5cmhWY1ZXK1VvS3d6SE80aUZHdWpmNDR0WHRydTY4L1NGVm5uVnRHWkYyKwo2WmJYeE81Z3I2c1NBQU9NK0E1RmtkQlNmcXZDdmwvUzZFQk04V2czaGNjOUZL
cEFCV0tadHNoRlMxOD0KLS0tLS1FTkQgQ0VSVElGSUNBVEUtLS0tLQo=
    server: https://172.16.0.11:6443
  name: kubernetes
contexts:contexts:
- context:
    cluster: kubernetes
    user: kubernetes-admin
  name: kubernetes-admin@kubernetes
current-context: kubernetes-admin@kubernetes
kind: Config
preferences: {}
users:
- name: kubernetes-admin
  user:
    client-certificate-data: LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0tLS0tCk1JSUM4akNDQWRxZ0F3SUJBZ0lJS2RLRGs4MUpNKzh3RFFZSktvWklodmNOQVFFTEJRQXdGVEVUTUJFR0ExVUUKQXhNS2EzVmlaWEp
1WlhSbGN6QWVGdzB5TURBME1UZ3hNelU0TXpKYUZ3MHlNVEEwTVRneE16VTRNelphTURReApGekFWQmdOVkJBb1REbk41YzNSbGJUcHRZWE4wWlhKek1Sa3dGd1lEVlFRREV4QnJkV0psY201bGRHVnpMV0ZrCmJXbHVNSUl
CSWpBTkJna3Foa2lHOXcwQkFRRUZBQU9DQVE4QU1JSUJDZ0tDQVFFQW44elI0RlVVM2F1QjluVGkKeWxJV1ZpZ3JkV1dHSXY0bmhsRnZuQU1mWVJyVklrMGN6eTZPTmZBQzNrb01tZ3ZPQnA5MmpsWmlvYXpJUGg1aAovaUR
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1TkNkeWp1cQpIVzQrMU5HdWZSczJWZW1kaGZZN2VORDJrSnJXNldHUnYyeWlBbDRQUGYzYURVbGpFYm9jVmx0RjZHTXhRRVU2CkJtaEJUWGMrVndaSXRzVnRPNTUzMHBDSmZwamJrRFZDZWFFUlBYK2RDd3hiTnh0ZWpacGZ
XT28zNGxTSGQ3TFYKRDc5UHAzYW1qQXpyamFqZE50QkdJeHFDc3lZWE9Rd1BVL2Nva1RJVHRHVWxLTVV5aUdOQk5rQ3NPc3RiZHI2RApnQVRuREg5YWdNck9CR2xVaUlJN0Qvck9rU3IzU2QvWnprSGdMM1c4a3V5dXFUWWp
wazNyNEFtU3NXS1M4UUdNCjZ6bHUwRk4rYnVJbGRvMnBLNmhBZlBnSTBjcDZWQWk1WW5lQVVGQ2EyL2pJeXI3cXRiND0KLS0tLS1FTkQgQ0VSVElGSUNBVEUtLS0tLQo=
    client-key-data: LS0tLS1CRUdJTiBSU0EgUFJJVkFURSBLRVktLS0tLQpNSUlFb3dJQkFBS0NBUUVBbjh6UjRGVVUzYXVCOW5UaXlsSVdWaWdyZFdXR0l2NG5obEZ2bkFNZllSclZJazBjCnp5Nk9OZkFDM2tvTW1
ndk9CcDkyamxaaW9heklQaDVoL2lEcWpRN3czeHBYVDdUMU9ZMksvZlcrdUtTUVFSN1UKTHVuMzgxMGhjVlFKbk1mZXhQYmxzNjZHdE94T1YvZFBtbXBBMlBZcy9JcFlrS1BIajZzb29DV1NSRDFGSHhtUgp1YWFheGkvSFh
Bd0k4NkQ3TW5ZL3QrNklBUjIrNlEzS2NqT0RXRFpUaWx2MjFwQlhQWnVvRU53aGdLNm1oSlFOClVGZzlWZUU0Q3g0SkQrYVhuYVJRbTMyd2J3b2hheTU4Ny9BZ1I0aDMzV04zSENYT1RlKytmeHpYQ0Z4cE9TVGIKbXc2TDV
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NaVdqeS9oWXpCVkFXZW9SU1lhWjNEeWVHRwpjRGNkZzZHQ3I5ZzNOVE1XdXpiWjRUOGRaT1JVTFQvZk1mSlljZm1iemFxcFlhZDlDVCtrR2FDMGZYcXJVemF5CmxQRkZvUUtCZ0E4ck5IeG1DaGhyT1ExZ1hET2FLcFJUUWN
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BZjZUMzM4Tjg5ZEo2Wi93QUlOdWNYCi0tLS0tRU5EIFJTQSBQUklWQVRFIEtFWS0tLS0tCg==

Not sure why most of the entries are null as shown below

$ sudo kubectl config view
  apiVersion: v1
  clusters: null
  contexts: null
  current-context: ""
  kind: Config
  preferences: {}
  users: null

Answer 1

Most probably the kubeconfig file is not setup properly.

 mkdir -p $HOME/.kube
 sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
 sudo chown $(id -u):$(id -g) $HOME/.kube/config

Alternatively, if you are the root user, you can run:

export KUBECONFIG=/etc/kubernetes/admin.conf

Also this should work

sudo kubectl get nodes --kubeconfig=/etc/kubernetes/admin.conf 

Answer 2

Changed environmental variable KUBECONFIG to /home/ltestzaman/.kube/config and it works

 $ echo $KUBECONFIG 
 /home/ltestzaman/.kube/config

$ kubectl get nodes --all-namespaces
  NAME             STATUS   ROLES    AGE    VERSION
  kubemaster-001   Ready    master   117m   v1.18.2

Or need to mention --config as identified by @Arghya Sadhu

 $ sudo kubectl get nodes --kubeconfig=/etc/kubernetes/admin.conf
   NAME             STATUS   ROLES    AGE    VERSION
   kubemaster-001   Ready    master   120m   v1.18.2