Exam-style
A ticketing platform sees traffic rise roughly thirtyfold in the ten minutes after a sale opens, hold for two hours, and return to its ordinary level. EC2 instances are launched automatically as demand rises and terminated automatically as it falls, and the bill covers only the time those instances ran. Which benefit of the AWS Cloud does this describe?
Reveal the answer
D. Elasticity, because capacity grows and shrinks automatically with demand
AWS defines elasticity as acquiring resources as you need them and releasing them when you no longer need them, automatically. Both halves are present here: instances are launched as load rises and terminated as it falls, and On-Demand instances are billed per second, so the charges fall away with the capacity. Scalability is the weaker claim. It covers handling more load by adding capacity, and carries no requirement that the capacity come back down afterwards. Agility is speed of access, new resources in minutes rather than the weeks a procurement cycle takes, so a team can try an idea and drop it again. High availability is the share of time a workload is available for use, usually reached by spreading redundant capacity across Availability Zones. Fault tolerance is the ability to withstand the failure of a subsystem, because a redundant one takes over its work. Neither of those last two describes an automatic scale-out and scale-in, even though the platform did stay up.
Q. Capacity is added automatically when a sale opens and released automatically two hours later, and the bill covers only the time it ran. Which benefit is that?
A. Elasticity. It covers the scale-in as well as the scale-out, and the fall in charges that follows.
Why? Scalability covers only making the system bigger to handle more load. Elasticity adds the automatic return to ordinary size, and On-Demand billing runs per second, so the charges come down with the capacity.