Cloud Computing Foundations
The Cloud Computing Foundations domain covers the vocabulary the rest of the exam builds on: what cloud computing actually is, the five essential characteristics that must all be present, and the economic logic behind adoption. EXIN tests definitions precisely, so most marks are lost by picking an answer that is almost right.
Definition
NIST SP 800-145 describes cloud computing as a model for enabling ubiquitous, on-demand network access to a shared pool of configurable computing resources that can be provisioned and released with minimal management effort. Three things follow: it is an operating model, not a product; resources are pooled and shared across consumers; and provisioning is self-service and rapid.
The five essential characteristics
- On-demand self-service: the consumer provisions capacity without human interaction with the provider.
- Broad network access: services are reachable over the network from heterogeneous client devices.
- Resource pooling: provider resources serve multiple consumers using a multi-tenant model.
- Rapid elasticity: capacity scales out and in, often automatically, appearing near-unlimited to the consumer.
- Measured service: usage is metered and billed, giving transparency to both parties.
A solution missing any one characteristic is not cloud computing. A virtualised data centre where users raise a ticket and wait three days fails self-service and rapid elasticity, however modern its hardware.
Why organisations adopt it
Cloud moves spend from capital expenditure, where servers are bought up front and depreciated, to operating expenditure billed by use. The exam links this to agility, faster time to market and avoiding over-provisioning for peak - not to a guarantee that cloud is always cheaper.
Worked example
A retailer runs a batch job needing 40 servers for three hours each night, and none for the other twenty-one. On-premises it must buy 40 servers sized for that peak. In cloud it launches 40 instances nightly and terminates them. Which characteristic justifies this? Reasoning: capacity is released as well as provisioned, automatically, on consumer demand - that is rapid elasticity. The nightly bill matching actual consumption is measured service. Scalability is the weaker distractor: it describes the ability to grow, not the ability to shrink automatically and pay only for what runs.
Traps that cost marks
- Treating cloud as a synonym for the internet, or for virtualisation.
- Confusing elasticity (automatic in and out) with scalability (capacity to grow).
- Assuming multi-tenancy is inherently insecure rather than a control to be assessed.
- Assuming cloud is always cheaper, ignoring integration, migration and egress costs.