Overview of Kubernetes Components and Plugins

Kubernetes (K8s) Components K8s clusters consist of core components, including Master and Worker nodes, which manage and run applications. The Master runs the API server, scheduler, etc., while Workers run kubelet and the container runtime.

Plugins extend K8s functionality. Examples include Network Plugins (e.g., Calico, Flannel), Volume Plugins (e.g., GlusterFS, NFS), and Ingress Plugins (e.g., Traefik, HAProxy) that provide networking, storage, and external traffic support.

Kubernetes DNS is a core component that resolves DNS queries for services and endpoints, enabling applications to access external resources via stable DNS names. It updates records automatically when services change.

Example commands for DNS:

kubectl run dns-example --image=dnsutils --restart=Never

kubectl exec -ti dns-example nslookup myservice.mydomain.com

cat <<eof | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: myservice
spec:
  selector:
    app: myapp
  ports:
  - port: 80
    targetPort: 8080
EOF

dig myservice.mydomain.com

Kubernetes Dashboard provides a graphical UI to view and manage cluster objects (nodes, pods, services, deployments) and supports monitoring, alerts, and auto‑completion.

kubectl proxy

kubectl get pods --namespace default

kubectl edit pods mypod --namespace=default

kubectl logs mypod --namespace=default

Heapster is a monitoring plugin that collects CPU, memory, and network metrics, sending them to tools like InfluxDB or Grafana.

helm install stable/heapster --name heapster

kubectl top pods

kubectl top pods --all-namespaces

heapster rules create rule.yml

Ingress Controller forwards external traffic into the cluster using Ingress resources, supporting load balancing and SSL termination.

helm install stable/nginx-ingress

cat <<eof | kubectl apply -f -
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: example-ingress
  annotations:
    ingress.kubernetes.io/ssl-redirect: "true"
spec:
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        backend:
          serviceName: example-service
          servicePort: 80
EOF

curl https://example.com/

Kubelet runs on each node as a daemon, receiving tasks from the API server, creating and destroying pods, and monitoring pod status.

cat <<eof | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
  - name: my-container
    image: nginx:latest
EOF

kubectl set image my-pod=my-image

kubectl delete pod my-pod

Container Runtime (Docker or compatible runtimes) provides the low‑level virtualization layer for K8s, handling image management, container execution, networking, and storage.

docker ps

docker pull <image>

docker images

docker run <image>

Network Plugin manages network connectivity on nodes. Types include Overlay (Flannel, Calico), Underlay, and CNI plugins.

helm install stable/flannel-crd --name flannel-crd

helm install stable/flannel --set network-plugin=flannel-crd --version=v0.9.1

kubectl get pods --output=jsonpath='{range .items[*]}{.status.podIP}{end}'

ip route show table local

dig @<pod-ip> <host>

Volume Plugin provides persistent storage for pods, supporting NFS, GlusterFS, AWS EBS, etc.

cat <<eof | kubectl apply -f -
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pv-claim
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 50Mi
EOF

cat <<eof | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
  - name: my-container
    image: nginx:latest
    volumeMounts:
    - mountPath: /data
      name: data-volume
  volumes:
  - name: data-volume
    persistentVolumeClaim:
      claimName: my-pv-claim
EOF

kubectl cp source-pod:/path/to/data destination-pod:/path/to/data

Ingress Plugin (e.g., NGINX, Traefik) enables external access, SSL, load balancing, and URL rewriting.

helm install stable/nginx-ingress

cat <<eof | kubectl apply -f -
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: example-ingress
  annotations:
    ingress.kubernetes.io/ssl-redirect: "true"
spec:
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        backend:
          serviceName: example-service
          servicePort: 80
EOF

kubectl patch secret example-secret -p '{"data":{"tls.crt":"$(cat cert.pem | base64 | tr -d '
')","tls.key":"$(cat key.pem | base64 | tr -d '
')"}}'

curl https://example.com/

Other Plugins such as Job, CronJob, Scheduler, and Autoscaler extend Kubernetes functionality for batch processing, scheduled tasks, pod placement, and automatic scaling.

cat <<eof | kubectl apply -f -
apiVersion: batch/v1
kind: Job
metadata:
  name: job-example
spec:
  template:
    spec:
      containers:
      - name: job-container
        image: busybox
        command: ["sh","-c","echo hello && sleep 30"]
      restartPolicy: OnFailure
EOF

cat <<eof | kubectl apply -f -
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: cron-job-example
spec:
  schedule: "*/5 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: cron-job-container
            image: busybox
            command: ["sh","-c","echo hello && sleep 30"]
          restartPolicy: OnFailure
EOF

helm install stable/scheduler --name scheduler-example

kubectl autoscale deployment example-deployment --min=1 --max=5