[k8s]After restarting the virtual machine, the kube-apiserver of k8s cannot start normally

After restarting the device:

kubectl get node
The connection to the server x.x.x.x:6443 was refused - did you specify the right host or port?
systemctl status kube-apiserver prompts:

Unit kube-apiserver.service could not be found
There is no such service, so it is judged that the configuration file is wrong

Decided to reconstruct the K8S cluster

Solution:

# 1. Check if kubectl command is working
kubectl get node

# 2. Go to the home directory
cd ~

# 3. Check if the .kube directory exists
ll -a  # List all files to check if .kube directory exists

# 4. Remove the .kube directory
sudo rm -rf .kube/

# 5. Restart Docker service
sudo systemctl restart docker  # Restart Docker

# 6. Restart kubelet service
sudo systemctl restart kubelet  # Restart kubelet

# 7. Reset the Kubernetes setup
sudo kubeadm reset  # Reset Kubernetes cluster

# 8. Remove CNI configurations
sudo rm -rf /etc/cni/  # Delete CNI configurations

# 9. Reinitialize Kubernetes with specific settings
kubeadm init --kubernetes-version=1.23.5 --apiserver-advertise-address=192.168.1.21 --image-repository registry.aliyuncs.com/google_containers --service-cidr=192.1.0.0/16 --pod-network-cidr=192.244.0.0/16

# 10. After successful initialization, configure Kubernetes for the user
mkdir -p $HOME/.kube  # Create the .kube directory
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config  # Copy admin config
sudo chown $(id -u):$(id -u) $HOME/.kube/config  # Change ownership of the config file

# 11. Download the Flannel network configuration file
wget https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml  # Download Flannel YAML file

# 12. Copy the kube-flannel.yml file to /opt and apply it
sudo cp kube-flannel.yml /opt/  # Copy the Flannel YAML file to /opt directory
kubectl apply -f /opt/kube-flannel.yml  # Apply the Flannel configuration

# After these steps, check the node status
kubectl get nodes  # Check if the node is ready

1. Issue with Flannel and CoreDNS Pods Not Starting: When checking the pods, Flannel and CoreDNS are not starting.

Error: Flannel is having an issue where it cannot obtain the necessary subnet lease. Specifically, the PodCIDR (assigned IP range for pods) 192.244.0.0/24 is not included within Flannel’s network configuration subnet 10.244.0.0/16.

1. Fixing the Subnet Configuration: Edit the Flannel ConfigMap: To resolve the subnet issue, the Flannel ConfigMap needs to be updated.

First, inspect the Flannel Pod:

kubectl describe pod kube-flannel-ds-99grr -n kube-flannel  # Describe the Flannel pod for detailed information

Check the logs:

kubectl logs kube-flannel-ds-fqvvv -n kube-flannel  # Check the Flannel pod logs for errors
Error Explanation: The Flannel network plugin is unable to get a subnet lease because the PodCIDR 192.244.0.0/24 is not within the subnet 10.244.0.0/16 specified in Flannel’s configuration.

Solution: You can resolve this by modifying the Flannel network configuration:

Edit the Flannel ConfigMap:

kubectl edit configmap kube-flannel-cfg -n kube-flannel  # Edit the Flannel ConfigMap in the kube-flannel namespace

Change the subnet in the ConfigMap to match the required PodCIDR.

After modifying the subnet in the kube-flannel-cfg ConfigMap, Flannel should be able to allocate the necessary subnets and the pods should start successfully.