Scaling & High Availability

Production Kubernetes clusters must handle variable load, survive infrastructure failures, and control costs. This lesson covers Horizontal Pod Autoscaler (HPA), Vertical Pod Autoscaler (VPA), Cluster Autoscaler, multi-AZ deployments, disaster recovery, and cost optimisation strategies.

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Autoscaling Overview

Type	What It Scales	Based On
HPA	Pod replicas	CPU, memory, custom metrics
VPA	Pod resource requests	Historical usage patterns
Cluster Autoscaler	Nodes	Pending pods with insufficient resources
KEDA	Pod replicas	Event-driven (queues, streams)

┌──────────────────────────────────────────────────────────┐
│                  Autoscaling Stack                        │
│                                                          │
│  ┌───────────┐  ┌───────────┐  ┌──────────────────────┐ │
│  │    HPA    │  │    VPA    │  │  Cluster Autoscaler  │ │
│  │ (pods)    │  │ (resources)│  │  (nodes)             │ │
│  └─────┬─────┘  └─────┬─────┘  └──────────┬───────────┘ │
│        │              │                    │             │
│        ▼              ▼                    ▼             │
│  ┌──────────────────────────────────────────────────┐   │
│  │              Kubernetes Cluster                   │   │
│  └──────────────────────────────────────────────────┘   │
└──────────────────────────────────────────────────────────┘

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Horizontal Pod Autoscaler (HPA)

HPA automatically adjusts the number of pod replicas based on observed metrics.