The ability to dynamically and automatically adjust cloud resources up or down based on actual demand in real-time. Like a balloon that expands and contracts based on how much air you put in.
During a viral marketing campaign, elastic cloud infrastructure automatically adds more servers as traffic spikes, then removes them when traffic returns to normal, optimizing costs.
All four provide automatic scaling of compute resources based on metrics (like CPU, requests, or queue depth). They differ mainly in supported resource types and how scaling policies/metrics are configured, but the goal is the same: add capacity during demand spikes and remove it when demand drops.