Kubernetes 101

free playground: https://kodekloud.com/public-playgrounds/multi-node-k8s-1-33/ second option: https://killercoda.com/playgrounds/scenario/kubernetes

Options: https://learn.kodekloud.com/user/courses/kubernetes-challenges Challenges are ree, but sign up is required

Lab 1 - RBAC Lab 2 - broken cluster, troobleshooting Lab3 - deployments and services Lab4 - highly available Redis Cluster

kubectl --help

alias for kubectl = k

k get nodes

Namespaces

k create ns k101

List all the namespaces now, you should see our namespace in the list

k get ns

Pods

vim pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  namespace: k101
spec:
  containers:
  - name: nginx
    image: nginx:1.14.2
    ports:
    - containerPort: 80

k apply -f pod.yaml

k get pods

Expect no pods found

Try with namespace:

k get pods -n k101

Depolyments

vim deploy.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  namespace: k101
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        resources:
          requests:
            memory: "64Mi"
            cpu: "250m"
        ports:
        - containerPort: 80

Create deployment:

k apply -f deploy.yaml

k get pods -n k101 --show-labels

k -n k101 delete pod nginx

k -n k101 get pods

k -n k101 delete pod nginx-deployment(press tab to use autocomplete)

Watch pod being re-created with a different name

Service

vim service.yaml

apiVersion: v1
kind: Service
metadata:
  name: my-service
  namespace: k101
spec:
  selector:
    app: nginx
  ports:
    - port: 80          # Port exposed by the service
      targetPort: 80    # Port on the Pod
      protocol: TCP     # TCP (default), UDP, or SCTP
  type: ClusterIP       # Service type

k run test --image=nginx -it --rm -n k101 -- sh

curl my-service

Kubernetes DNS Naming Convention

The URL my-service.k101.svc.cluster.local follows Kubernetes' DNS naming convention and breaks down as follows:

my-service - The name of the Service resource as defined in your service.yaml k101 - The namespace where the Service is deployed svc - Indicates this is a Service resource type cluster.local - The default DNS domain for the Kubernetes cluster

This follows the standard Kubernetes DNS pattern:

<service-name>.<namespace>.svc.cluster.local

This DNS structure allows pods within the cluster to reliably communicate with services using consistent naming, regardless of the actual pod IPs or locations. The example shows accessing the nginx service from a test pod created in the same namespace.

You can also use shorter forms within the same namespace (just my-service) or from other namespaces (my-service.k101)

Scaling

vim hpa.yaml

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: k101-hpa
  namespace: k101
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: nginx-deployment
  minReplicas: 1
  maxReplicas: 10
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 50

k apply -f hpa.yaml

We need metrics server worker, which we don't have in the playground.

Install metrics server to see it working:

kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml

kubectl patch -n kube-system deployment metrics-server --type=json -p '[{"op":"add","path":"/spec/template/spec/containers/0/args/-","value":"--kubelet-insecure-tls"}]'

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Wifi: networks: Loungeroom username: rgroup4 password: 8605

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Vim help:

To enter insert mode: i To save and exit: :x To exit no saving :q!