Elasticity

The ability to match capacity to demand in both directions and pay only for what is used. It is the main economic argument of the cloud, and only works with stateless, quick-to-start components.

Where it shows up in real systems

  • Auto-scaling group

    Instances are added when CPU exceeds the target and removed when it falls. New instances need a warm-up period before taking traffic, so sudden spikes still hurt: keep enough minimum capacity. Failed instances are replaced automatically.

    In production: AWS Auto Scaling groups, Azure VM Scale Sets, GCP Managed Instance Groups, Kubernetes HPA

  • Serverless function

    There is no server to size: capacity is the concurrency limit. When traffic rises faster than warm instances exist, requests pay a cold start, which is much longer for Java than for Go. Very cheap at low volume, expensive at a steady high volume.

    In production: AWS Lambda, Azure Functions, Google Cloud Functions, Cloudflare Workers

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