Kubernetes basics

Instruction

Control plane vs worker nodes

Control Plane:

• The control plane is installed on your master node
• Can be both a control plane node and a worker node
• It houses the API server, scheduler, and controller manager settings

Worker Nodes:

• This is where the kubelet and kube-proxy are installed
• You can use the kubeadm join command to join workers to the master node to form the cluster

Common commands

kubectl

myapp.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: memory-demo
  namespace: mem-example
spec:
  containers:
  - name: memory-demo-ctr
    image: polinux/stress
    resources:
      requests:
        memory: "100Mi"
      limits:
        memory: "200Mi"
    command: ["stress"]
    args: ["--vm", "1", "--vm-bytes", "150M", "--vm-hang", "1"]

# Create a namespace mem-example
kubectl create namespace mem-example

# Create a pod memory-demo
kubectl apply -f myapp.yaml

# VerifyCheck the podnodes
kubectl get nodes
kubectl describe nodes

# Check the pods
kubectl get pods
kubectl get all -A
kubectl get pod memory-demo --namespace=mem-example
kubectl get pod memory-demo --output=yaml --namespace=mem-example
kubectl top pod memory-demo --namespace=mem-example
kubectl describe pod memory-demo --namespace=mem-example

# Delete a pod
kubectl delete pod memory-demo --namespace=mem-example

Networking

Inbound Rules for K3s Nodes

Protocol	Port	Source	Destination	Description
TCP	2379-2380	Servers	Servers	Required only for HA with embedded etcd
TCP	6443	Agents	Servers	K3s supervisor and Kubernetes API Server
UDP	8472	All nodes	All nodes	Required only for Flannel VXLAN
TCP	10250	All nodes	All nodes	Kubelet metrics
UDP	51820	All nodes	All nodes	Required only for Flannel Wireguard with IPv4
UDP	51821	All nodes	All nodes	Required only for Flannel Wireguard with IPv6
TCP	5001	All nodes	All nodes	Required only for embedded distributed registry (Spegel)
TCP	6443	All nodes	All nodes	Required only for embedded distributed registry (Spegel)

Typically, all outbound traffic is allowed.