Kubernetes Master Worker Node Kubeadm Join issue

Question

I am installing Kubernetes on Oracle Virtualbox in my laptop using Kubeadm . Everything worked fine till i run this command on Kuberenets Worker node to join with Master node I got the error after running

sudo kubeadm join 192.168.56.100:6443 --token 0i2osm.vsp2mk63v1ypeyjf     --discovery-token-ca-cert-hash sha256:18511321fcc4b622628dd1ad2f56dbdd319bf024740d58127818720828cc7bf0

Error

[preflight] Running pre-flight checks
        [WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
error execution phase preflight: [preflight] Some fatal errors occurred:
        [ERROR DirAvailable--etc-kubernetes-manifests]: /etc/kubernetes/manifests is not empty
        [ERROR FileAvailable--etc-kubernetes-kubelet.conf]: /etc/kubernetes/kubelet.conf already exists
        [ERROR Port-10250]: Port 10250 is in use
        [ERROR FileAvailable--etc-kubernetes-pki-ca.crt]: /etc/kubernetes/pki/ca.crt already exists
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`

I tried deleting files manually and ran the command again but it didnt resolve the port issue . and whenever i stop the kubectl which is running on 10250 port and then run the command it gives error to " kubectl needs to be started and when i start the kubectl then it gives error for port 10250 is in use "

Its a kind of chicken and egg thing

Any views on how i can resolve it ?

Answer 1

you should first try

 #kubeadm reset 

because you already have kubernetes it gets error.

Answer 2

Regarding kubeadm reset:

1 ) As describe here:

The "reset" command executes the following phases:

preflight              Run reset pre-flight checks
update-cluster-status  Remove this node from the ClusterStatus object.
remove-etcd-member     Remove a local etcd member.
cleanup-node           Run cleanup node.

So I recommend to run the preflight phase first (by using the --skip-phases flag) before executing the all phases together.

2 ) When you execute the cleanup-node phase you can see that the following steps are being logged:

.
.

[reset] Stopping the kubelet service

[reset] Unmounting mounted directories in "/var/lib/kubelet"

[reset] Deleting contents of config directories: [
/etc/kubernetes/manifests 
/etc/kubernetes/pki
]

[reset] Deleting files: [
/etc/kubernetes/admin.conf 
/etc/kubernetes/kubelet.conf 
/etc/kubernetes/bootstrap-kubelet.conf 
/etc/kubernetes/controller-manager.conf 
/etc/kubernetes/scheduler.conf
]

.
.

Let's go over the [reset] entries and see how they solve the 4 errors you mentioned:

A ) The first [reset] entry will fix the Port 10250 is in use issue (kubelet was listening on this port).

B ) The fourth [reset] entry will fix the two errors of /etc/kubernetes/manifests is not empty and /etc/kubernetes/kubelet.conf already exists.

C ) And we're left with the /etc/kubernetes/pki/ca.crt already exists error.
I thought that the third [reset] entry of removing /etc/kubernetes/pki should take care of that.
But, in my case when I ran the kubeadm join with verbosity level of 5 (by appending the --v=5 flag) I encounter the error below:

I0929 ... checks.go:432] validating if ...
[preflight] Some fatal errors occurred:
[ERROR FileAvailable-etc-kubernetes-pki-ca.crt]: /etc/kubernetes/pki/ca.crt already exists

So I had to remove the /etc/kubernetes/pki folder manually and then the kubeadm join was successful again.