How to fix Unable to connect to the server: Service Unavailable in Kubernetes

# SSH into a control plane node
ssh <control-plane-node>

# Check if API server pod is running
sudo docker ps | grep kube-apiserver
# or for containerd:
sudo crictl ps | grep kube-apiserver

# Check pod status in kube-system namespace
kubectl get pod -n kube-system | grep kube-apiserver

# View pod logs
kubectl logs -n kube-system kube-apiserver-<node-name>

# For self-managed clusters, delete the pod to force restart
kubectl delete pod -n kube-system kube-apiserver-<node-name>

# The static pod controller will automatically recreate it
# Wait 30-60 seconds for it to come back online

sleep 30
kubectl get pod -n kube-system kube-apiserver-<node-name>

# SSH to control plane node
ssh <control-plane-node>

# Check etcd pod status
sudo crictl ps | grep etcd

# Test etcd connectivity (from API server container)
sudo crictl exec <etcd-container-id> etcdctl endpoint health

# Check etcd logs
sudo crictl logs <etcd-container-id> | tail -50

# Get the API server endpoint
grep server ~/.kube/config
# Example: https://192.168.1.10:6443

# Test connectivity from your machine
curl -k https://<api-server-ip>:6443/version

# Test from a pod inside the cluster
kubectl run -it debug --image=alpine --restart=Never -- sh
# Inside pod:
apk add curl
curl -k https://kubernetes.default:6443/version

# Check if port 6443 is listening
netstat -tlnp | grep 6443

# View current kubeconfig
kubectl config view

# Check the server endpoint
grep server ~/.kube/config

# If incorrect, update it
kubectl config set-cluster kubernetes --server=https://correct-ip:6443

# Verify with a simple test
kubectl cluster-info

# SSH to control plane
ssh <control-plane-node>

# Check system resources
free -h  # Memory
df -h    # Disk space

# Check if API server was OOMKilled
journalctl -xe | grep -i oomkiller

# Edit API server resource requests/limits
kubectl edit -n kube-system deployment kube-apiserver
# or for static pod:
sudo vim /etc/kubernetes/manifests/kube-apiserver.yaml

# Increase resources:
spec:
  containers:
  - name: kube-apiserver
    resources:
      requests:
        cpu: 500m
        memory: 1Gi
      limits:
        memory: 2Gi

# Check certificate expiry
echo | openssl s_client -connect <api-server-ip>:6443 2>/dev/null | openssl x509 -noout -dates

# If expired, regenerate cluster certificates
kubeadm certs renew all

# Restart control plane components
kubectl rollout restart deployment -n kube-system

# For managed clusters, use cloud provider certificate rotation

# SSH to control plane
ssh <control-plane-node>

# Check system status
systemctl status kubelet
systemctl status docker  # or containerd

# View kubelet logs
journalctl -u kubelet -n 50

# Check kernel logs for crashes
journalctl -xe | tail -100

# Monitor disk space (etcd issue if full)
df -h /var/lib/etcd

# Restart kubelet if necessary
sudo systemctl restart kubelet