Rapid elasticity

Rapid elasticity is the ability to provision and release computing capacity quickly in response to demand, often automatically. The consumer may experience capacity as readily available even though the provider operates finite physical resources.^[ref]

For example, a service can add workers when its queue grows and remove them after the backlog clears. A control rule needs an observation signal, a scaling policy and time for new workers to become ready. Elastic capacity does not make every program parallel: a serial bottleneck, shared database or slow startup can prevent additional workers from increasing throughput. Releasing capacity also requires preserving needed state outside workers that may disappear.