Kubernetes Introduction

Kubernetes (K8s) is an open-source container orchestration platform. It automates deploying, scaling, and managing containerised applications across a cluster of machines.

Why Kubernetes Exists

Docker solves packaging. Kubernetes solves operations at scale.

Without orchestration you face:

Manual restarts when containers crash
No built-in load balancing across replicas
No rolling deployments without downtime
No automatic scaling under load

Kubernetes handles all of this declaratively — you describe desired state, and the control plane makes it reality.

Architecture Overview

Control Plane (manages the cluster)
├── API Server       — single entry point for all operations
├── etcd             — distributed key-value store for cluster state
├── Scheduler        — assigns pods to nodes based on resources
└── Controller Manager — reconciliation loops (deployments, replicas, etc.)

Worker Nodes (run the workloads)
├── kubelet          — agent that runs pods on the node
├── kube-proxy       — network rules and service routing
└── Container Runtime — containerd or Docker

Key Concepts

Concept	What it is
Pod	Smallest deployable unit — one or more containers
Node	A machine (VM or physical) in the cluster
Cluster	One control plane + multiple worker nodes
Namespace	Logical partition within a cluster
Deployment	Manages replicas and rolling updates of pods
Service	Stable network endpoint in front of pods
ConfigMap / Secret	External configuration and sensitive values
Ingress	HTTP routing from outside the cluster to services

Kubernetes vs Plain Docker

Concern	Docker alone	Kubernetes
Container restart on crash	Manual or restart policy	Automatic
Load balancing	Manual with nginx/HAProxy	Built-in via Services
Rolling updates	Manual scripting	`kubectl rollout`
Auto-scaling	Not built-in	HorizontalPodAutoscaler
Multi-host networking	Complex setup	Built-in overlay network

Use plain Docker for local development and single-host deployments. Use Kubernetes when you need multi-node workloads, auto-scaling, or zero-downtime deployments.

When to Use Kubernetes

Good fit:

Microservices with independent scaling requirements
High-availability production workloads
Teams that ship frequently and need zero-downtime deploys

Might be overkill:

Small single-service apps
Prototypes or internal tools
Teams without operational capacity to maintain a cluster (consider managed alternatives like Cloud Run or Azure Container Apps)

Managed Kubernetes Options

All major clouds offer managed control planes so you only manage worker nodes:

GKE — Google Kubernetes Engine
AKS — Azure Kubernetes Service
EKS — Amazon Elastic Kubernetes Service

Next Steps

Pods — the smallest deployable unit
Deployments — running and updating replicas
Services — exposing pods on the network
kubectl Commands — essential CLI reference