cluster-upgrade.sh

#!/bin/bash
# Cluster upgrade procedure (e.g., 1.30 → 1.31)
# Run on each node, control plane first
set -euo pipefail

TARGET_VERSION="${1:?Usage: $0 <target-version> (e.g., 1.31.0)}"
NODE_NAME=$(hostname)
ROLE="${2:-worker}"  # "control-plane" or "worker"

echo "=== Upgrading $NODE_NAME ($ROLE) to v${TARGET_VERSION} ==="

# Step 1: Drain the node (run from a machine with kubectl access)
echo "[1/5] Drain node..."
echo "  kubectl drain $NODE_NAME --ignore-daemonsets --delete-emptydir-data"

# Step 2: Upgrade kubeadm
echo "[2/5] Upgrading kubeadm..."
sudo apt-get update
sudo apt-get install -y --allow-change-held-packages kubeadm="${TARGET_VERSION}-*"
kubeadm version

# Step 3: Apply upgrade
if [ "$ROLE" = "control-plane" ]; then
  echo "[3/5] Planning upgrade..."
  sudo kubeadm upgrade plan

  echo "[3/5] Applying upgrade..."
  sudo kubeadm upgrade apply "v${TARGET_VERSION}" --yes
else
  echo "[3/5] Upgrading worker node config..."
  sudo kubeadm upgrade node
fi

# Step 4: Upgrade kubelet and kubectl
echo "[4/5] Upgrading kubelet and kubectl..."
sudo apt-get install -y --allow-change-held-packages \
  kubelet="${TARGET_VERSION}-*" \
  kubectl="${TARGET_VERSION}-*"

sudo systemctl daemon-reload
sudo systemctl restart kubelet

# Step 5: Uncordon
echo "[5/5] Uncordon node..."
echo "  kubectl uncordon $NODE_NAME"

echo "=== Done. Verify with: kubectl get nodes ==="