(centos) k8s-update.sh – script to upgrade a kubernetes cluster

Script to update a kubernetes cluster to the next patch or minor version.

#!/bin/bash

# if no parameter, show versions and syntax
if [ -z $1 ]; then
  # show available versions
  yum list --showduplicates kubeadm --disableexcludes=kubernetes

  # show syntax
  echo ""
  echo "Syntax:"
  echo "$0 <version>, e.g. $0 1.26.x-0"
  exit 1
fi

# remember version
export TARGET_VERSION=$1


# configure kubectl to use admin config
export KUBECONFIG=/etc/kubernetes/admin.conf

# track first control plane node
export IS_FIRST=1

# loop through control plane nodes
#kubectl get nodes --no-headers | xargs -n 5 echo
NODES=`kubectl get nodes --no-headers | awk '{print $1}'`
for NODE in $NODES; do
  # parse kubectl node output into parameters
  NODE_HOSTNAME=`kubectl get node $NODE --no-headers | xargs -n 5 bash -c 'echo $0'`
  NODE_TYPE=`kubectl get node $NODE --no-headers | xargs -n 5 bash -c 'echo $2'`
  NODE_VERSION=`kubectl get node $NODE --no-headers | xargs -n 5 bash -c 'echo $4'`

  # only work on control plane nodes in this loop
  if [ $NODE_TYPE != "control-plane" ]; then
     #echo ""
     #echo "skipping worker node"
     continue
  fi

  echo ""
  echo "***"
  echo "* Next: $NODE_HOSTNAME"

  # upgrade kubeadm
  echo "upgrade to: $TARGET_VERSION"
  ssh root@$NODE_HOSTNAME yum install -y kubeadm-$TARGET_VERSION --disableexcludes=kubernetes

  # verify the download works and has the expected version
  #ssh root@$NODE_HOSTNAME kubeadm version

  # verify the upgrade plan
  #ssh root@$NODE_HOSTNAME kubeadm upgrade plan

  # perform the update
  if [ $IS_FIRST == "0" ]; then
    ssh root@$NODE_HOSTNAME kubeadm upgrade node
  else
    # if this is the first control plane node its command is a little different
    ssh root@$NODE_HOSTNAME kubeadm upgrade apply --yes v$TARGET_VERSION

    # adjust tracking now that we've completed the first control plane node
    export IS_FIRST=0
  fi

  # drain node & prepare for updating
  kubectl drain $NODE_HOSTNAME --delete-emptydir-data --ignore-daemonsets

  # update kubelet & kubectl
  ssh root@$NODE_HOSTNAME yum install -y kubelet-$TARGET_VERSION kubectl-$TARGET_VERSION --disableexcludes=kubernetes

  # restart kubelet
  ssh root@$NODE_HOSTNAME systemctl daemon-reload
  ssh root@$NODE_HOSTNAME systemctl restart kubelet

  # uncordon the node
  kubectl uncordon $NODE_HOSTNAME
  
done


# loop through worker nodes
NODES=`kubectl get nodes --no-headers | awk '{print $1}'`
for NODE in $NODES; do
  # parse kubectl node output into parameters
  NODE_HOSTNAME=`kubectl get node $NODE --no-headers | xargs -n 5 bash -c 'echo $0'`
  NODE_TYPE=`kubectl get node $NODE --no-headers | xargs -n 5 bash -c 'echo $2'`
  NODE_VERSION=`kubectl get node $NODE --no-headers | xargs -n 5 bash -c 'echo $4'`

  # only work on control plane nodes in this loop
  if [ $NODE_TYPE == "control-plane" ]; then
     #echo ""
     #echo "skipping control plane node"
     continue
  fi

  echo ""
  echo "***"
  echo "* Next: $NODE_HOSTNAME"

  # upgrade kubeadm
  echo "upgrade to: $TARGET_VERSION"
  ssh root@$NODE_HOSTNAME yum install -y kubeadm-$TARGET_VERSION --disableexcludes=kubernetes

  # verify the download works and has the expected version
  #ssh root@$NODE_HOSTNAME kubeadm version

  # verify the upgrade plan
  #ssh root@$NODE_HOSTNAME kubeadm upgrade plan

  # perform the update
  if [ $IS_FIRST == "0" ]; then
    ssh root@$NODE_HOSTNAME kubeadm upgrade node
  fi

  # drain node & prepare for updating
  kubectl drain $NODE_HOSTNAME --delete-emptydir-data --ignore-daemonsets

  # update kubelet & kubectl
  ssh root@$NODE_HOSTNAME yum install -y kubelet-$TARGET_VERSION kubectl-$TARGET_VERSION --disableexcludes=kubernetes

  # restart kubelet
  ssh root@$NODE_HOSTNAME systemctl daemon-reload
  ssh root@$NODE_HOSTNAME systemctl restart kubelet

  # uncordon the node
  kubectl uncordon $NODE_HOSTNAME
  
done