What is Kubernetes?

☸️ What is Kubernetes?

Kubernetes (K8s) is an open-source container orchestration platform used to:

• Deploy
• Scale
• Manage containerized applications (Docker containers)

🧱 Kubernetes Architecture

🔹 Control Plane

• API Server – Entry point
• etcd – Key-value store (cluster data)
• Scheduler – Assigns pods to nodes
• Controller Manager – Maintains desired state

🔹 Worker Node

• kubelet – Communicates with control plane
• Container Runtime – Docker / containerd
• kube-proxy – Networking

📦 Core Kubernetes Components

1️⃣ Pod

• Smallest deployable unit
• Contains one or more containers

2️⃣ Deployment

• Manages Pods
• Supports scaling & rolling updates

3️⃣ Service

• Exposes Pods to network
• Types:
• ClusterIP
• NodePort
• LoadBalancer

4️⃣ Namespace

• Logical separation inside cluster

5️⃣ ConfigMap & Secret

• ConfigMap – Non-sensitive config
• Secret – Passwords, tokens

🌐 Kubernetes Networking (Interview Important)

• Every Pod gets its own IP
• Pods can communicate without NAT
• Service provides stable IP

📈 Scaling

kubectl scale deployment app --replicas=3

🔄 Rolling Update

kubectl rollout status deployment app

Rollback:

kubectl rollout undo deployment app

📄 Basic YAML Example

apiVersion: apps/v1

kind: Deployment

metadata:

name: myapp

spec:

replicas: 2

selector:

matchLabels:

app: myapp

template:

metadata:

labels:

app: myapp

spec:

containers:

- name: web

image: nginx

ports:

- containerPort: 80

Apply:

kubectl apply -f app.yaml

🔧 Common kubectl Commands

kubectl get pods

kubectl get nodes

kubectl describe pod podname

kubectl logs podname

🔐 Security Basics

• RBAC
• Network Policies
• Secrets
• Pod Security