What is Kubernetes and why is it used?

Kubernetes (K8s) is an open-source container orchestration platform that automates deployment, scaling, and management of containerised applications.

**Key concepts:**
- **Pod** — smallest unit, runs one or more containers
- **Deployment** — manages replica sets, handles rolling updates
- **Service** — exposes pods to network (load balancing)
- **Ingress** — manages external HTTP/HTTPS access
- **ConfigMap/Secret** — manage configuration and credentials

**Why Kubernetes:**
1. Auto-healing — restarts failed containers
2. Auto-scaling — adds pods when CPU/memory is high
3. Rolling updates — deploy new version with zero downtime
4. Service discovery — pods find each other automatically
5. Multi-cloud — runs on AWS (EKS), Azure (AKS), GCP (GKE)

**Without K8s:** You manually manage where each container runs.
**With K8s:** Declare desired state, K8s ensures it's always true.