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 scale-out/scale-in for compute instances based on metrics (e.g., CPU, requests) and can be paired with load balancers. They differ mainly in configuration style, metric sources, and ecosystem integrations, but the core elasticity outcome is the same: match capacity to demand.