kubectl get nodes

This command lists all nodes in the Kubernetes cluster. It provides basic details about each node, such as its status, roles, age, and version.

NAME           STATUS   ROLES    AGE    VERSION
node-1        Ready    master   10d    v1.25.0
node-2        Ready    worker   5d     v1.25.0
node-3        Ready    worker   5d     v1.25.0

• NAME → Name of the node.
• STATUS → Whether the node is Ready (healthy) or NotReady (unhealthy).
• ROLES → The role of the node (master or worker).
• AGE → How long ago the node was created.
• VERSION → Kubernetes version running on the node.

kubectl get pods

This command lists all running and pending pods in the current namespace.

NAME         READY   STATUS    RESTARTS   AGE
nginx-pod   1/1     Running   0          2h
db-pod      0/1     Pending   0          5m

• NAME → The name of the pod.
• READY → How many containers are running in the pod vs. the total number of containers.
• STATUS → The current status (Running, Pending, CrashLoopBackOff, etc.).
• RESTARTS → Number of times the pod has restarted.
• AGE → How long the pod has been running.

apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: webserver
spec:
  containers:
  - name: nginx-container
    image: nginx:latest
    ports:
    - containerPort: 80

• apiVersion: v1 → The Kubernetes API version.
• kind: Pod → The type of resource.
• metadata: → Contains the pod’s name and labels.
• spec: → Defines the specification for the pod.
• containers: → Specifies the container(s) inside the pod.
• image: nginx:latest → The image for the container.
• ports: → Exposes port 80 inside the container.

kubectl apply -f pod.yaml

kubectl get pods -o wide

This command provides additional details about the pods, including node name, IP addresses, and container images.

NAME         READY   STATUS    RESTARTS   AGE   IP           NODE        NOMINATED NODE   READINESS GATES
nginx-pod   1/1     Running   0          2h    10.42.0.5    node-1      <none>           <none>
db-pod      0/1     Pending   0          5m    <none>       node-2      <none>           <none>

• IP → The internal IP of the pod.
• NODE → The node on which the pod is running.
• NOMINATED NODE → Shows if a node has been nominated for scheduling.
• READINESS GATES → If the pod has readiness conditions to meet.

kubectl describe pod nginx-pod

This command provides detailed information about a specific pod, including events, labels, IP, node, and status.

Name:         nginx-pod
Namespace:    default
Node:         node-1/192.168.1.10
Start Time:   Thu, 30 Mar 2023 14:00:00 +0530
Labels:       app=webserver
Status:       Running
IP:           10.42.0.5
Containers:
  nginx-container:
    Container ID:   docker://abcdef12345
    Image:          nginx:latest
    Ports:          80/TCP
    State:          Running
Events:
  Type    Reason     Age   From              Message
  ----    ------     ---   ----              -------
  Normal  Scheduled  2h    default-scheduler Successfully assigned nginx-pod to node-1
  Normal  Pulled     2h    kubelet           Container image "nginx:latest" already present on machine

• Node: The node on which the pod is running.
• Labels: Labels assigned to the pod.
• Status: The pod's status.
• IP: The internal IP of the pod.
• Events: Logs of actions related to the pod.

kubectl apply -f pod.yaml

This command applies the configuration defined in pod.yaml to create or update a Pod in the Kubernetes cluster. If the Pod does not exist, it is created. If it already exists, Kubernetes updates it to match the new configuration.

The -f flag specifies the file containing the desired configuration. It tells Kubernetes to read from pod.yaml and apply the changes accordingly.

When you run kubectl apply -f pod.yaml, Kubernetes reads the file and ensures that the defined resources are created or updated accordingly.

kubectl delete pod <pod-name>

This command deletes the specified pod from the cluster. Once deleted, the pod cannot be recovered, but if a Deployment or ReplicaSet is managing the pod, Kubernetes may automatically recreate it.

kubectl delete pod nginx-pod

• kubectl delete pod nginx-pod → Deletes the nginx-pod.
• If the pod is managed by a Deployment or ReplicaSet, it will be recreated automatically.
• If the pod is standalone, it will be permanently removed.

After deletion, you can verify using:

kubectl get pods

This command lists remaining pods, confirming the deletion.

A label is a key-value pair attached to a Kubernetes resource (such as Pods, Nodes, or Services). Labels help identify and group related objects.

labels:
  key: value

apiVersion: v1
kind: Pod
metadata:
  name: web-pod
  labels:
    app: webserver
    environment: production
spec:
  containers:
  - name: nginx-container
    image: nginx:latest

kubectl get pods --show-labels

Add a Label to an Existing Pod:

kubectl label pod web-pod team=frontend

Remove a Label:

kubectl label pod web-pod team-

apiVersion: v1
kind: Service
metadata:
  name: web-service
spec:
  selector:
    app: webserver
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

• selector: Ensures this Service applies only to Pods with app: webserver.
• port: 80 → Exposes the service on port 80.
• targetPort: 80 → Routes traffic to Pods running on port 80.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: webserver
  template:
    metadata:
      labels:
        app: webserver
    spec:
      containers:
      - name: nginx-container
        image: nginx:latest

• The Deployment creates 3 Pods.
• All Pods are labeled app: webserver.
• The selector ensures that only Pods with app: webserver are managed by this Deployment.