Читать книгу CompTIA Cloud+ Study Guide - Ben Piper, David Higby Clinton - Страница 98

The ability of the cloud to scale resources up or down rapidly to match demand is called elasticity. For IaaS services, this can be done automatically as needed using autoscaling. This allows cloud consumers to scale up automatically as their workload increases and then have the cloud remove the services after the workload subsides. For SaaS and PaaS services, dynamic allocation of resources occurs automatically and is handled by the cloud provider. (Later in the chapter, we'll discuss the division of responsibilities between you and the provider.) With elastic computing, there is no longer any need to deploy servers and storage systems designed to handle peak loads—servers and systems that may otherwise sit idle during normal operations. Now you can scale the cloud infrastructure to the normal load and automatically expand as needed when the occasion arises.

On-demand cloud services allow the cloud customer to create instantly additional servers, storage, processing power, or any other services as required. On-demand allows customers to consume cloud services only as needed and scale back when they are no longer required. For example, if a developer needs to provision a database and application server for testing, they can quickly provision these servers and deprovision them once they're no longer needed. This is also referred to as a just-in-time service because it allows cloud services to be added and removed as needed.

Pay as you grow (PAYG) is like a basic utility, such as power or water, where you pay for only what you use. This is very cost effective because there are minimal up-front costs, and the ongoing costs track your actual consumption of the service. The elasticity of the cloud lets you add resources on-demand, so there's no need to overprovision for future growth. With a normal data center operation, the computing must be overprovisioned to take into account peak usage or future requirements that may never be needed.