[Kubernetes]Drain and Uncordon node for node upgrade in Kubernetes

Purpose

Kubelet, kubectl, kubeadm version upgrade

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Work process

1. 노드 업그레이드 순서 kubeadm upgrade → kubelet, kubectl upgrade
   1. 기본 컨트롤 플레인 노드를 업그레이드한다.
   2. 추가 컨트롤 플레인 노드를 업그레이드한다.
   3. 워커(worker) 노드를 업그레이드한다.

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Master node

1. kubeadm upgrade

Check version

kubeadm version

Decision version

## yum list 에서 확인
yum list --showduplicates kubeadm --disableexcludes=kubernetes

>> 1.21.4-0

Master node drain

master $ kubectl drain controlplane --ignore-daemonsets

master $ kubectl get nodes
NAME           STATUS                     ROLES    AGE   VERSION
controlplane   Ready,SchedulingDisabled   master   17m   v1.18.0
node01         Ready                      <none>   17m   v1.18.0

Master node upgrade

## 위에서 확인한 버전 install
yum install -y kubeadm-1.19.x-0 --disableexcludes=kubernetes
yum install -y kubeadm-1.21.4-0 --disableexcludes=kubernetes
[Y]

## upgrade plan 확인
kubeadm upgrade plan

## 업그레이드 적용 (첫 번째 컨트롤플레인 노드에서 아래 명령 실행)
kubeadm upgrade apply v1.19.0 
kubeadm upgrade apply v1.21.4
## 첫번째 이후 다른 컨트롤 플레인 노드의 경우 아래명령 실행
kubeadm upgrade node 

## upgrade version 확인
kubeadm version

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2. kubelet, kubectl upgrade

Kubelet & Kubectl upgrade

## yum list 에서 확인
yum list --showduplicates kubelet kubectl --disableexcludes=kubernetes

>> 1.21.4-0

apt install kubelet=1.19.0-00
yum install -y kubelet-1.19.x-0 kubectl-1.19.x-0 --disableexcludes=kubernetes
yum install -y kubelet-1.21.4-0 kubectl-1.21.4-0 --disableexcludes=kubernetes

Restart kubelet

sudo systemctl daemon-reload
sudo systemctl restart kubelet

kubelet --version
kubectl version --short

Uncordon

kubectl uncordon controlplane

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Worker node

1. Kubeadm upgrade

Work node drain

kubectl drain node01 --ignore-daemonsets

Worker node kubeadm upgrade

ssh node01

## controlPlane node 와 버전을 맞춘다
## install kubeadm
yum install -y kubeadm-1.19.x-0 --disableexcludes=kubernetes
yum install -y kubeadm-1.21.4-0 --disableexcludes=kubernetes

## upgrade kubeadm
kubeadm upgrade node

## check version
kubeadm version

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2. kubelet, kubectl upgrade

Worker node kubelet, kubeadm upgrade

yum install -y kubelet-1.19.x-0 kubectl-1.19.x-0 --disableexcludes=kubernetes
yum install -y kubelet-1.21.4-0 kubectl-1.21.4-0 --disableexcludes=kubernetes

Restart kubelet

sudo systemctl daemon-reload
sudo systemctl restart kubelet
kubelet --version

master $ kubectl get nodes
NAME           STATUS                     ROLES    AGE   VERSION
controlplane   Ready                      master   32m   v1.19.0
node01         Ready,SchedulingDisabled   <none>   31m   v1.19.0

Uncordon

kubectl uncordon <node-to-drain>