Читать книгу The Official (ISC)2 CCSP CBK Reference - Leslie Fife, Aaron Kraus - Страница 25

In a traditional computing model, a company would need to buy the infrastructure needed for any future, potential, or anticipated growth. If they estimate poorly, they either will have a lot of excess capacity or will run out of room. Neither situation is optimal. In a cloud solution, the space needed grows and shrinks as necessary to support the customer. If there is a peak in usage or resource needs, the service grows with the needs. When the needs are gone, the resources used decrease. This supports a pay-as-you-go model, where a customer pays only for the resources needed and used.

For the CSP, this presents a challenge. The CSP must have the excess capacity to serve all their customers without having to incur the cost of the total possible resource usage. They must, in effect, estimate how much excess capacity they must have to serve all of their customers. If they estimate poorly, the customer will suffer and the CSP's customer base could decrease.

However, there is a cost to maintaining this excess capacity. The cost must be built into the cost model. In this way, all customers share in the cost of the CSP, maintaining some level of excess capacity. In the banking world, a bank must keep cash reserves of a certain percentage so that they can meet the withdrawal needs of their customers. But if every customer wanted all of their money at the same time, the bank would run out of cash on hand. In the same way, if every customer's potential peak usage occurred at the same time, the CSP would run out of resources, and the customers would be constrained (and unhappy).

The customer must also take care in setting internal limits on resource use. The ease of expanding resource use can make it easy to consume more resources than are truly necessary. Rather than cleaning up and returning resources no longer needed, it is easy to just spin up more resources. If care is not taken to set limits, a customer can find themselves with a large and unnecessary bill for resources “used.”