my-docs/Containerization & Orchestration/Kubernetes/3-Commands.md

Below is an enhanced version of your Kubernetes Command Reference. This revision further refines the structure, improves consistency, and adds a few extra sections for clarity and ease of use.

---

Kubernetes Command Reference

This guide provides a concise reference for common kubectl commands used to manage Kubernetes clusters. Whether you’re managing nodes, namespaces, pods, deployments, or autoscaling, the examples below will help you perform everyday tasks with confidence.

---

Table of Contents

• Kubernetes Command Reference
  • Table of Contents
  • General Commands
  • Node Management
    • Listing Nodes
    • Labeling Nodes
    • Node Maintenance (Cordon/Drain)
  • Namespace Management
  • Pod Management
    • Listing Pods
    • Running a Pod
    • Deleting a Pod
  • API Resources & Documentation
  • Logs & Pod Information
  • Applying YAML Files
  • Viewing Cluster Resources
  • ReplicaSet & Deployment Management
    • Scaling and Rollouts
    • Autoscaling
  • Port Forwarding
  • Additional Information

---

General Commands

• List API Resources
  Display all available API resources along with their short names:

  kubectl api-resources
  

---

Node Management

Listing Nodes

• Show All Nodes

  kubectl get nodes
  

Labeling Nodes

• Set a Custom Label on a Node

  kubectl label node <node-name> kubernetes.io/<label-key>=<label-value>
  

  Note: Replace <node-name>, <label-key>, and <label-value> with your desired values.

Node Maintenance (Cordon/Drain)

• Cordon a Node
  Prevent new pods from being scheduled on the node.

  kubectl cordon <node-name>
  

• Uncordon a Node
  Mark the node as schedulable again.

  kubectl uncordon <node-name>
  

• Drain a Node
  Evict all pods from the node (excluding those managed by DaemonSets).

  kubectl drain <node-name> --ignore-daemonsets --delete-local-data
  

  Warning: Draining a node will evict running pods. Ensure that you plan this action to avoid service disruption.

---

Namespace Management

• List All Namespaces

  kubectl get namespaces
  # Or the shorthand:
  kubectl get ns
  

• Create a New Namespace

  kubectl create namespace <namespace-name>
  

---

Pod Management

Listing Pods

• List Pods in the Default Namespace

  kubectl get pods
  

• List Pods with Detailed Information (Wide Output)

  kubectl get pods -o wide
  

• List Pods in a Specific Namespace

  kubectl get pods -o wide -n <namespace-name>
  

Running a Pod

Note: The kubectl run command is best suited for running single pods. For more complex deployments, consider using YAML manifests.

• Basic Example:

  kubectl run <pod-name> --image=<image-name> --port=<port-number> -n <namespace-name>
  

• Advanced Example with Multiple Options:

  kubectl run mypod --image=nginx --port=80 -n mynamespace \
    --env="ENV_VAR_NAME=VALUE" --command -- nginx -g "daemon off;" \
    --restart=Always --dry-run=client \
    --labels="app=myapp,env=prod" \
    --limits=cpu=100m,memory=256Mi --requests=cpu=50m,memory=128Mi
  

  Common Options Explained:

  • --image: Container image to use.
  • --port: Port exposed by the container.
  • -n or --namespace: Namespace in which to run the pod.
  • --env: Set environment variables.
  • --command: Treat the following arguments as the command to run.
  • --restart: Pod restart policy (Always, OnFailure, or Never).
  • --labels: Assign labels to the pod.
  • --dry-run: Validate the command without creating the pod.
  • --limits and --requests: Define resource limits and requests for the container.

Deleting a Pod

• Delete a Pod in a Specific Namespace

  kubectl delete pod <pod-name> -n <namespace-name>
  

---

API Resources & Documentation

• Get Detailed Documentation for an API Resource

  kubectl explain <api-resource-name>
  

  Example:

  kubectl explain pod
  

---

Logs & Pod Information

• Stream Logs for a Running Pod

  kubectl logs -f -n <namespace-name> <pod-name>
  

• Get Detailed Information About a Pod

  kubectl describe pod <pod-name> -n <namespace-name>
  

---

Applying YAML Files

• Apply a Configuration from a YAML File

  Apply a YAML configuration to a specific namespace:

  kubectl apply -f <yaml-file> -n <namespace-name>
  

---

Viewing Cluster Resources

• Display All Resources in a Namespace

  kubectl get all -n <namespace-name>
  

• Display ReplicaSets, Pods, and Deployments in a Specific Namespace

  kubectl get rs,pods,deployments -n <namespace-name>
  

---

ReplicaSet & Deployment Management

Scaling and Rollouts

• Scale a ReplicaSet

  kubectl scale rs <replicaset-name> --replicas=<count> -n <namespace-name>
  

• View Rollout History of a Deployment

  kubectl rollout history deployment <deployment-name> -n <namespace-name>
  

• View Details of a Specific Revision

  kubectl rollout history deployment <deployment-name> -n <namespace-name> --revision=<number>
  

• Roll Back a Deployment to a Specific Revision

  kubectl rollout undo deployment <deployment-name> -n <namespace-name> --to-revision=<number>
  

Autoscaling

• Autoscale a Deployment
  Automatically scale a deployment based on CPU utilization:

  kubectl autoscale deployment <deployment-name> -n <namespace-name> --cpu-percent=<target-cpu-percentage> --min=<min-pods> --max=<max-pods>
  

• View Horizontal Pod Autoscalers (HPA)

  kubectl get hpa -n <namespace-name>
  

---

Port Forwarding

Sometimes you need to access a service or pod directly from your local machine. Use the following command to forward a port:

kubectl port-forward -n <namespace-name> svc/<service-name> <local-port>:<target-port>

Example: Forward local port 8080 to port 80 of the service named my-service in the mynamespace namespace:

kubectl port-forward -n mynamespace svc/my-service 8080:80

---

Additional Information

• Static Manifest Files
  Any YAML files placed in /etc/kubernetes/manifests/ are automatically loaded when the kubelet starts (for example, after a server reboot).