What is Kubernetes?

1

What is Kubernetes?

Kubernetes is an open-source container orchestration platform.
Originally developed by Google, now maintained by CNCF.
Automates deployment, scaling and management of containerized apps.
Also known as K8s (K + 8 letters + s).
Works with Docker, containerd, CRI-O runtimes.

Kubernetes Stack

Your App (Containers)

↓

Pods

↓

⎈ Kubernetes

↓

Nodes / Infra

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Why Kubernetes?

⚡

Auto Scaling

Scale up/down based on load automatically

🔄

Self Healing

Restarts crashed containers automatically

🔁

Rolling Updates

Zero-downtime deployments

⚖

Load Balancing

Distributes traffic across pods

🔧

Bin Packing

Optimally places containers on nodes

🔒

Secrets Mgmt

Manages sensitive config data

⭐ Remember

✓ Kubernetes does NOT run your code -- it orchestrates containers

✓ K8s = open-source, cloud-native, declarative configuration

💡 Interview Tip

Q: What is Kubernetes?
A: Kubernetes is an open-source container orchestration platform that automates deployment, scaling, and management of containerized applications.

Kubernetes Architecture

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Cluster Overview

🧠 Control Plane (Master)

API Server

etcd

Scheduler

Controller Manager

↕ communicates via API

Worker Node 1

kubelet

kube-proxy

Pod

Worker Node 2

kubelet

kube-proxy

Pod

2

Control Plane vs Worker Nodes

Control Plane

Worker Node

kube-apiserver -- central gateway

kubelet -- node agent

etcd -- key-value store

kube-proxy -- network rules

kube-scheduler -- assigns pods

Container Runtime (Docker/CRI-O)

controller-manager -- maintains state

Pods run here

⭐ Key Points

✓ etcd stores all cluster state

✓ API Server is the only entry point

✓ Scheduler only assigns, doesn't run pods

💡 Interview Tip

Q: What is etcd?
A: etcd is a distributed key-value store that stores the entire cluster state and configuration.

Pods & Deployments

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What is a Pod?

Smallest deployable unit in Kubernetes
Contains one or more containers
Containers share network & storage
Has a unique IP address inside the cluster
Ephemeral -- pods can die and be replaced

Pod

Container 1

Container 2

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What is a Deployment?

Manages ReplicaSets of pods
Declares desired state (e.g., "3 replicas")
Handles rolling updates & rollbacks
Self-heals -- replaces failed pods automatically

Deployment

↓ manages

ReplicaSet (replicas: 3)

↓ creates

Pod

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Pod Lifecycle

Pending
Scheduled, not started

→

Running
At least one container running

→

Succeeded
All containers exited 0

or

Failed
Container exited non-zero

💡 Interview Tip

Q: Difference between Pod and Deployment?
A: A Pod is a single instance of your app. A Deployment manages a group of identical pods with features like scaling, rolling updates, and self-healing.

Services & Networking

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What is a Service?

A stable network endpoint to expose pods
Pods have dynamic IPs -- Services give a stable IP
Acts as a load balancer across pod replicas
Uses label selectors to find target pods

Client

↓

Service (stable IP)

↓ routes to

Pod

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Types of Services

Type

Access

Use Case

ClusterIP

Only within cluster

Internal microservice comms

NodePort

External via Node IP:Port

Dev/Testing exposure

LoadBalancer

External via Cloud LB

Production traffic (AWS/GCP)

ExternalName

DNS CNAME to external

Access external DB etc.

3

Ingress

HTTP/HTTPS routing to services
Supports host-based routing
Supports path-based routing
Requires an Ingress Controller (nginx, traefik)

💡 Interview Tip

Q: LoadBalancer vs Ingress?
A: LoadBalancer per-service (expensive). Ingress is one entry point routing to multiple services -- better for HTTP.

Config, Secrets & Volumes

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ConfigMap

Stores non-sensitive configuration data
Key-value pairs or entire config files
Injected as env vars or mounted as volumes
Example: DB host, app port, feature flags

apiVersion: v1
kind: ConfigMap
data:
  DB_HOST: "postgres"
  APP_PORT: "8080"

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Secrets

Stores sensitive data (passwords, tokens)
Base64 encoded (NOT encrypted by default!)
Should enable etcd encryption at rest
Types: Opaque, TLS, docker-registry

apiVersion: v1
kind: Secret
type: Opaque
data:
  password: cGFzc3dvcmQ=

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Volumes & Persistent Storage

emptyDir

Temp storage, deleted when pod dies

hostPath

Mounts node filesystem path

PersistentVolume

Cluster-wide storage resource (PV)

PVC

Pod's claim to use a PV

⭐ ConfigMap vs Secret

✓ ConfigMap = non-sensitive config, plain text

✓ Secret = sensitive data, base64 encoded (enable encryption at rest!)

Use Cases & Quick Reference

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Real-World Use Cases

Microservices

Run 100s of microservices independently, scale each separately

CI/CD Pipelines

Jenkins, ArgoCD, Tekton run on K8s for build and deploy

ML Workloads

GPU workloads, model training and serving at scale

Multi-Cloud

Portable workloads across AWS, GCP, Azure

Data Platforms

Kafka, Spark, Flink run on Kubernetes clusters

E-Commerce

Netflix, Airbnb, Spotify scale on demand

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kubectl Quick Reference

kubectl get pods

List all pods

kubectl describe pod <name>

Detailed pod info

kubectl logs <pod>

View pod logs

kubectl apply -f file.yaml

Deploy from YAML

kubectl delete pod <name>

Delete a pod

kubectl scale deploy/app --replicas=5

Scale deployment

⭐ K8s Cheat Sheet

✓ Pod -- smallest unit

✓ Deployment -- manages ReplicaSets

✓ Service -- stable network endpoint

✓ Ingress -- HTTP routing gateway

✓ ConfigMap -- non-sensitive config

✓ Secret -- sensitive data

💡 Final Tip

Practice: Install minikube locally and deploy a simple app. Hands-on experience beats 10x reading!

minikube start