kubeadm Cheatsheet

kubeadm is used for managing k8s clusters.

Full life-cycle:

• kubeadm init: bootstrap the first node.
• kubeadm join: bootstrap more nodes and join to the cluster.
• kubeadm upgrade: upgrade a Kubernetes cluster to a newer version; perform the upgrade of etcd by default.
• kubeadm reset: performs a best effort revert of changes made to this host by kubeadm init or kubeadm join.

NOT in scope:

• provisioning machines: use metal3 for provisioning bare-metal machines.
• installing addons, e.g. dashboard, monitoring solutions, and cloud-specific addons, etc.

Used by other tools like minikube, kind, etc.

Commands

Token

Create token

$ kubeadm token create

List token

$ kubeadm token list

Init

$ kubeadm init --control-plane-endpoint=$IPADDR  --apiserver-cert-extra-sans=$IPADDR  --pod-network-cidr=$POD_CIDR --node-name $NODENAME --ignore-preflight-errors Swap

$ kubeadm init --pod-network-cidr=192.168.0.0/16

Join as a worker node

Print join command

$ kubeadm token create --print-join-command
# this will print something like this:
# kubeadm join 10.200.xxx.xxx:443 --token 0iyxxx.72o1s06xxxxxxx --discovery-token-ca-cert-hash sha256:xxxxxxxxxxxxxx

Join:

$ kubeadm join --token TOKEN MASTER_IP:MASTER_PORT --discovery-token-ca-cert-hash sha256:HASH

$ kubeadm join phase control-plane-prepare certs --config /dev/stdin --v 5

Join as a control-plane node

--certificate-key string: When used together with '--print-join-command', print the full 'kubeadm join' flag needed to join the cluster as a control-plane. To create a new certificate key you must use 'kubeadm init phase upload-certs --upload-certs'.

Tear down a node

$ kubectl drain NODE --delete-local-data --force --ignore-daemonsets
$ kubectl delete node NODE
$ kubeadm reset

To force reset:

$ kubeadm reset --force

Config

Get Pod and Service CIDRs

$ kubeadm config view | grep Subnet

Dump config

$ cd /etc
$ kubeadm config view > kubeadmconf.yaml

Get kubeconfig

$ kubeadm kubeconfig user --client-name kubernetes-admin

Troubleshooting

Port 10250 is in use

kubeadm may throw error: Port 10250 is in use.

10250 is used by kubelet.

$ lsof -i:10250
COMMAND   PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
kubelet 68360 root   18u  IPv6  473103      0t0  TCP *:10250 (LISTEN)

Try to kill the existing kubelet.