Elasticity
Automatically adding or removing resources to match real-time demand.
Elasticity is the ability of a cloud system to automatically provision and release resources in response to real-time demand, so compute capacity tracks actual workload rather than a fixed estimate. On AWS this is delivered primarily through Auto Scaling groups, which add EC2 instances when CPU or request metrics spike and terminate them when demand subsides, with billing adjusting accordingly. The exam often contrasts elasticity with scalability: scalability means a system can handle more load (it has the headroom), while elasticity means it automatically does so, expanding and contracting without manual intervention. Scalability is a design property; elasticity is the dynamic, automated behavior built on top of it.
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