Kubernetes Introduction

📘 What is Kubernetes?

Kubernetes is an open-source container orchestration platform originally developed by Google (now maintained by the Cloud Native Computing Foundation - CNCF).

It automates the deployment, scaling, and management of containerized applications (like Docker containers).

👉 Think of Kubernetes as the "operating system for your data center/cloud" that manages all your containerized workloads.

🕰️ A Quick History

2014 → Google open-sourced Kubernetes.
2015 → Donated to CNCF.
Inspired by Google’s internal system Borg, which ran containers at massive scale.
Today, Kubernetes is the industry standard for container orchestration.

⚙️ Why Do We Need Kubernetes?

Containers (like Docker) are great but managing them at scale is hard:

How do you restart a failed container?
How do you scale up/down when traffic changes?
How do you load-balance across containers?
How do you roll out updates without downtime?

👉 Kubernetes solves all of this automatically.

🧩 Key Concepts in Kubernetes

1️⃣ Cluster

A Kubernetes cluster consists of:

Master Node (Control Plane) → Manages the cluster (scheduler, API server, controller).
Worker Nodes → Where containers (Pods) actually run.

2️⃣ Pod

The smallest deployable unit in Kubernetes.

A Pod wraps one or more containers (usually 1).

Example: A Pod could run a web server container + a logging sidecar container.

3️⃣ Deployment

Defines the desired state of Pods (e.g., 3 replicas of Nginx). Kubernetes ensures the cluster always matches this state.

Example: If 1 Pod crashes, Deployment brings it back automatically.

4️⃣ Service

Provides networking and load balancing for Pods. Since Pods are ephemeral (they come and go), a Service gives them a stable IP and DNS name.

5️⃣ Ingress

Manages external access to Services (HTTP/HTTPS). Lets you expose apps to the internet with domain names, SSL, routing, etc.

6️⃣ ConfigMaps & Secrets

ConfigMap → Store configuration (key-value pairs).
Secret → Store sensitive data (like API keys, passwords).

7️⃣ Autoscaling

Horizontal Pod Autoscaler (HPA) → Increases/decreases Pod replicas based on CPU/memory usage.

🚀 Example: Running Nginx in Kubernetes

nginx-deployment.yaml


apiVersion: apps/v1
kind: Deployment

metadata:
  name: nginx-deployment

spec:
  replicas: 3

  selector:
    matchLabels:
      app: nginx

template:
  metadata:
    labels:
      app: nginx

  spec:
    containers:
      - name: nginx
        image: nginx:latest
        ports:
          - containerPort: 80

nginx-service.yaml

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80
  type: LoadBalancer

👉 Run:

kubectl apply -f nginx-deployment.yaml kubectl apply -f nginx-service.yaml

Now you have 3 replicas of Nginx running behind a load-balanced service.

🌟 Advantages of Kubernetes

Self-healing → Restarts failed containers, replaces Pods, reschedules workloads.
Scalability → Auto-scales applications up or down.
Portability → Works on any cloud (AWS, Azure, GCP) or on-prem.
Load Balancing & Networking → Distributes traffic across Pods.
Rolling Updates & Rollbacks → Deploy updates without downtime.
Resource Efficiency → Optimizes CPU/memory usage.
Ecosystem & Extensibility → Works with Helm charts, Operators, Service Meshes, etc.

🔑 Real-World Use Cases

Running microservices architectures.
Hosting scalable web apps & APIs.
CI/CD pipelines (Jenkins, GitLab runners on Kubernetes).
Big Data & AI workloads (TensorFlow on K8s).
Hybrid cloud strategy → Run the same workloads on-prem & cloud.

Essential kubectl CLI Commands 🧵

🚀 Basic Setup & Cluster Info

Command	Usage
kubectl version	Show client and server version.
kubectl cluster-info	Display cluster info.
kubectl config view	View kubeconfig settings.
kubectl config use-context	Switch to a different cluster context.

📦 Pods

Command	Usage
kubectl get pods	List all pods in the current namespace.
kubectl get pods -A	List pods across all namespaces.
kubectl describe pod	Show details of a pod.
kubectl logs	View logs of a pod.
kubectl exec -it -- sh	Access a pod's shell.

🚀 Deployments

Command	Usage
kubectl get deployments	List deployments.
kubectl create deployment --image=	Create a new deployment.
kubectl scale deployment --replicas=	Scale a deployment.
kubectl rollout status deployment/	Check rollout status.
kubectl rollout undo deployment/	Rollback a deployment.

🌐 Services & Networking

Command	Usage
kubectl get services	List all services.
kubectl expose deployment --port= --type=NodePort	Expose a deployment as a service.
kubectl port-forward svc/ :	Forward local port to service.

📁 Config & Secrets

Command	Usage
kubectl get configmaps	List all configmaps.
kubectl create configmap --from-literal=key=value	Create configmap from literal values.
kubectl get secrets	List secrets.
kubectl create secret generic --from-literal=key=value	Create secret from literal values.

🔄 Namespace Management

Command	Usage
kubectl get namespaces	List all namespaces.
kubectl create namespace	Create a new namespace.
kubectl delete namespace	Delete a namespace.

🧹 Cleanup

Command	Usage
kubectl delete pod	Delete a pod.
kubectl delete deployment	Delete a deployment.
kubectl delete service	Delete a service.
kubectl delete all --all	Delete all resources in the namespace.

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